1 // SPDX-License-Identifier: GPL-2.0-only
2 #define pr_fmt(fmt) "SMP alternatives: " fmt
3
4 #include <linux/mmu_context.h>
5 #include <linux/perf_event.h>
6 #include <linux/vmalloc.h>
7 #include <linux/memory.h>
8 #include <linux/execmem.h>
9
10 #include <asm/text-patching.h>
11 #include <asm/insn.h>
12 #include <asm/insn-eval.h>
13 #include <asm/ibt.h>
14 #include <asm/set_memory.h>
15 #include <asm/nmi.h>
16
17 int __read_mostly alternatives_patched;
18
19 EXPORT_SYMBOL_GPL(alternatives_patched);
20
21 #define MAX_PATCH_LEN (255-1)
22
23 #define DA_ALL (~0)
24 #define DA_ALT 0x01
25 #define DA_RET 0x02
26 #define DA_RETPOLINE 0x04
27 #define DA_ENDBR 0x08
28 #define DA_SMP 0x10
29
30 static unsigned int debug_alternative;
31
debug_alt(char * str)32 static int __init debug_alt(char *str)
33 {
34 if (str && *str == '=')
35 str++;
36
37 if (!str || kstrtouint(str, 0, &debug_alternative))
38 debug_alternative = DA_ALL;
39
40 return 1;
41 }
42 __setup("debug-alternative", debug_alt);
43
44 static int noreplace_smp;
45
setup_noreplace_smp(char * str)46 static int __init setup_noreplace_smp(char *str)
47 {
48 noreplace_smp = 1;
49 return 1;
50 }
51 __setup("noreplace-smp", setup_noreplace_smp);
52
53 #define DPRINTK(type, fmt, args...) \
54 do { \
55 if (debug_alternative & DA_##type) \
56 printk(KERN_DEBUG pr_fmt(fmt) "\n", ##args); \
57 } while (0)
58
59 #define DUMP_BYTES(type, buf, len, fmt, args...) \
60 do { \
61 if (unlikely(debug_alternative & DA_##type)) { \
62 int j; \
63 \
64 if (!(len)) \
65 break; \
66 \
67 printk(KERN_DEBUG pr_fmt(fmt), ##args); \
68 for (j = 0; j < (len) - 1; j++) \
69 printk(KERN_CONT "%02hhx ", buf[j]); \
70 printk(KERN_CONT "%02hhx\n", buf[j]); \
71 } \
72 } while (0)
73
74 static const unsigned char x86nops[] =
75 {
76 BYTES_NOP1,
77 BYTES_NOP2,
78 BYTES_NOP3,
79 BYTES_NOP4,
80 BYTES_NOP5,
81 BYTES_NOP6,
82 BYTES_NOP7,
83 BYTES_NOP8,
84 #ifdef CONFIG_64BIT
85 BYTES_NOP9,
86 BYTES_NOP10,
87 BYTES_NOP11,
88 #endif
89 };
90
91 const unsigned char * const x86_nops[ASM_NOP_MAX+1] =
92 {
93 NULL,
94 x86nops,
95 x86nops + 1,
96 x86nops + 1 + 2,
97 x86nops + 1 + 2 + 3,
98 x86nops + 1 + 2 + 3 + 4,
99 x86nops + 1 + 2 + 3 + 4 + 5,
100 x86nops + 1 + 2 + 3 + 4 + 5 + 6,
101 x86nops + 1 + 2 + 3 + 4 + 5 + 6 + 7,
102 #ifdef CONFIG_64BIT
103 x86nops + 1 + 2 + 3 + 4 + 5 + 6 + 7 + 8,
104 x86nops + 1 + 2 + 3 + 4 + 5 + 6 + 7 + 8 + 9,
105 x86nops + 1 + 2 + 3 + 4 + 5 + 6 + 7 + 8 + 9 + 10,
106 #endif
107 };
108
109 #ifdef CONFIG_FINEIBT
110 static bool cfi_paranoid __ro_after_init;
111 #endif
112
113 #ifdef CONFIG_MITIGATION_ITS
114
115 #ifdef CONFIG_MODULES
116 static struct module *its_mod;
117 #endif
118 static void *its_page;
119 static unsigned int its_offset;
120 struct its_array its_pages;
121
__its_alloc(struct its_array * pages)122 static void *__its_alloc(struct its_array *pages)
123 {
124 void *page __free(execmem) = execmem_alloc_rw(EXECMEM_MODULE_TEXT, PAGE_SIZE);
125 if (!page)
126 return NULL;
127
128 void *tmp = krealloc(pages->pages, (pages->num+1) * sizeof(void *),
129 GFP_KERNEL);
130 if (!tmp)
131 return NULL;
132
133 pages->pages = tmp;
134 pages->pages[pages->num++] = page;
135
136 return no_free_ptr(page);
137 }
138
139 /* Initialize a thunk with the "jmp *reg; int3" instructions. */
its_init_thunk(void * thunk,int reg)140 static void *its_init_thunk(void *thunk, int reg)
141 {
142 u8 *bytes = thunk;
143 int offset = 0;
144 int i = 0;
145
146 #ifdef CONFIG_FINEIBT
147 if (cfi_paranoid) {
148 /*
149 * When ITS uses indirect branch thunk the fineibt_paranoid
150 * caller sequence doesn't fit in the caller site. So put the
151 * remaining part of the sequence (UDB + JNE) into the ITS
152 * thunk.
153 */
154 bytes[i++] = 0xd6; /* UDB */
155 bytes[i++] = 0x75; /* JNE */
156 bytes[i++] = 0xfd;
157
158 offset = 1;
159 }
160 #endif
161
162 if (reg >= 8) {
163 bytes[i++] = 0x41; /* REX.B prefix */
164 reg -= 8;
165 }
166 bytes[i++] = 0xff;
167 bytes[i++] = 0xe0 + reg; /* JMP *reg */
168 bytes[i++] = 0xcc;
169
170 return thunk + offset;
171 }
172
its_pages_protect(struct its_array * pages)173 static void its_pages_protect(struct its_array *pages)
174 {
175 for (int i = 0; i < pages->num; i++) {
176 void *page = pages->pages[i];
177 execmem_restore_rox(page, PAGE_SIZE);
178 }
179 }
180
its_fini_core(void)181 static void its_fini_core(void)
182 {
183 if (IS_ENABLED(CONFIG_STRICT_KERNEL_RWX))
184 its_pages_protect(&its_pages);
185 kfree(its_pages.pages);
186 }
187
188 #ifdef CONFIG_MODULES
its_init_mod(struct module * mod)189 void its_init_mod(struct module *mod)
190 {
191 if (!cpu_feature_enabled(X86_FEATURE_INDIRECT_THUNK_ITS))
192 return;
193
194 mutex_lock(&text_mutex);
195 its_mod = mod;
196 its_page = NULL;
197 }
198
its_fini_mod(struct module * mod)199 void its_fini_mod(struct module *mod)
200 {
201 if (!cpu_feature_enabled(X86_FEATURE_INDIRECT_THUNK_ITS))
202 return;
203
204 WARN_ON_ONCE(its_mod != mod);
205
206 its_mod = NULL;
207 its_page = NULL;
208 mutex_unlock(&text_mutex);
209
210 if (IS_ENABLED(CONFIG_STRICT_MODULE_RWX))
211 its_pages_protect(&mod->arch.its_pages);
212 }
213
its_free_mod(struct module * mod)214 void its_free_mod(struct module *mod)
215 {
216 if (!cpu_feature_enabled(X86_FEATURE_INDIRECT_THUNK_ITS))
217 return;
218
219 for (int i = 0; i < mod->arch.its_pages.num; i++) {
220 void *page = mod->arch.its_pages.pages[i];
221 execmem_free(page);
222 }
223 kfree(mod->arch.its_pages.pages);
224 }
225 #endif /* CONFIG_MODULES */
226
its_alloc(void)227 static void *its_alloc(void)
228 {
229 struct its_array *pages = &its_pages;
230 void *page;
231
232 #ifdef CONFIG_MODULES
233 if (its_mod)
234 pages = &its_mod->arch.its_pages;
235 #endif
236
237 page = __its_alloc(pages);
238 if (!page)
239 return NULL;
240
241 if (pages == &its_pages)
242 set_memory_x((unsigned long)page, 1);
243
244 return page;
245 }
246
its_allocate_thunk(int reg)247 static void *its_allocate_thunk(int reg)
248 {
249 int size = 3 + (reg / 8);
250 void *thunk;
251
252 #ifdef CONFIG_FINEIBT
253 /*
254 * The ITS thunk contains an indirect jump and an int3 instruction so
255 * its size is 3 or 4 bytes depending on the register used. If CFI
256 * paranoid is used then 3 extra bytes are added in the ITS thunk to
257 * complete the fineibt_paranoid caller sequence.
258 */
259 if (cfi_paranoid)
260 size += 3;
261 #endif
262
263 if (!its_page || (its_offset + size - 1) >= PAGE_SIZE) {
264 its_page = its_alloc();
265 if (!its_page) {
266 pr_err("ITS page allocation failed\n");
267 return NULL;
268 }
269 memset(its_page, INT3_INSN_OPCODE, PAGE_SIZE);
270 its_offset = 32;
271 }
272
273 /*
274 * If the indirect branch instruction will be in the lower half
275 * of a cacheline, then update the offset to reach the upper half.
276 */
277 if ((its_offset + size - 1) % 64 < 32)
278 its_offset = ((its_offset - 1) | 0x3F) + 33;
279
280 thunk = its_page + its_offset;
281 its_offset += size;
282
283 return its_init_thunk(thunk, reg);
284 }
285
its_static_thunk(int reg)286 u8 *its_static_thunk(int reg)
287 {
288 u8 *thunk = __x86_indirect_its_thunk_array[reg];
289
290 #ifdef CONFIG_FINEIBT
291 /* Paranoid thunk starts 2 bytes before */
292 if (cfi_paranoid)
293 return thunk - 2;
294 #endif
295 return thunk;
296 }
297
298 #else
its_fini_core(void)299 static inline void its_fini_core(void) {}
300 #endif /* CONFIG_MITIGATION_ITS */
301
302 /*
303 * Nomenclature for variable names to simplify and clarify this code and ease
304 * any potential staring at it:
305 *
306 * @instr: source address of the original instructions in the kernel text as
307 * generated by the compiler.
308 *
309 * @buf: temporary buffer on which the patching operates. This buffer is
310 * eventually text-poked into the kernel image.
311 *
312 * @replacement/@repl: pointer to the opcodes which are replacing @instr, located
313 * in the .altinstr_replacement section.
314 */
315
316 /*
317 * Fill the buffer with a single effective instruction of size @len.
318 *
319 * In order not to issue an ORC stack depth tracking CFI entry (Call Frame Info)
320 * for every single-byte NOP, try to generate the maximally available NOP of
321 * size <= ASM_NOP_MAX such that only a single CFI entry is generated (vs one for
322 * each single-byte NOPs). If @len to fill out is > ASM_NOP_MAX, pad with INT3 and
323 * *jump* over instead of executing long and daft NOPs.
324 */
add_nop(u8 * buf,unsigned int len)325 static void add_nop(u8 *buf, unsigned int len)
326 {
327 u8 *target = buf + len;
328
329 if (!len)
330 return;
331
332 if (len <= ASM_NOP_MAX) {
333 memcpy(buf, x86_nops[len], len);
334 return;
335 }
336
337 if (len < 128) {
338 __text_gen_insn(buf, JMP8_INSN_OPCODE, buf, target, JMP8_INSN_SIZE);
339 buf += JMP8_INSN_SIZE;
340 } else {
341 __text_gen_insn(buf, JMP32_INSN_OPCODE, buf, target, JMP32_INSN_SIZE);
342 buf += JMP32_INSN_SIZE;
343 }
344
345 for (;buf < target; buf++)
346 *buf = INT3_INSN_OPCODE;
347 }
348
349 /*
350 * Find the offset of the first non-NOP instruction starting at @offset
351 * but no further than @len.
352 */
skip_nops(u8 * buf,int offset,int len)353 static int skip_nops(u8 *buf, int offset, int len)
354 {
355 struct insn insn;
356
357 for (; offset < len; offset += insn.length) {
358 if (insn_decode_kernel(&insn, &buf[offset]))
359 break;
360
361 if (!insn_is_nop(&insn))
362 break;
363 }
364
365 return offset;
366 }
367
368 /*
369 * "noinline" to cause control flow change and thus invalidate I$ and
370 * cause refetch after modification.
371 */
optimize_nops(const u8 * const instr,u8 * buf,size_t len)372 static void noinline optimize_nops(const u8 * const instr, u8 *buf, size_t len)
373 {
374 for (int next, i = 0; i < len; i = next) {
375 struct insn insn;
376
377 if (insn_decode_kernel(&insn, &buf[i]))
378 return;
379
380 next = i + insn.length;
381
382 if (insn_is_nop(&insn)) {
383 int nop = i;
384
385 /* Has the NOP already been optimized? */
386 if (i + insn.length == len)
387 return;
388
389 next = skip_nops(buf, next, len);
390
391 add_nop(buf + nop, next - nop);
392 DUMP_BYTES(ALT, buf, len, "%px: [%d:%d) optimized NOPs: ", instr, nop, next);
393 }
394 }
395 }
396
397 /*
398 * In this context, "source" is where the instructions are placed in the
399 * section .altinstr_replacement, for example during kernel build by the
400 * toolchain.
401 * "Destination" is where the instructions are being patched in by this
402 * machinery.
403 *
404 * The source offset is:
405 *
406 * src_imm = target - src_next_ip (1)
407 *
408 * and the target offset is:
409 *
410 * dst_imm = target - dst_next_ip (2)
411 *
412 * so rework (1) as an expression for target like:
413 *
414 * target = src_imm + src_next_ip (1a)
415 *
416 * and substitute in (2) to get:
417 *
418 * dst_imm = (src_imm + src_next_ip) - dst_next_ip (3)
419 *
420 * Now, since the instruction stream is 'identical' at src and dst (it
421 * is being copied after all) it can be stated that:
422 *
423 * src_next_ip = src + ip_offset
424 * dst_next_ip = dst + ip_offset (4)
425 *
426 * Substitute (4) in (3) and observe ip_offset being cancelled out to
427 * obtain:
428 *
429 * dst_imm = src_imm + (src + ip_offset) - (dst + ip_offset)
430 * = src_imm + src - dst + ip_offset - ip_offset
431 * = src_imm + src - dst (5)
432 *
433 * IOW, only the relative displacement of the code block matters.
434 */
435
436 #define apply_reloc_n(n_, p_, d_) \
437 do { \
438 s32 v = *(s##n_ *)(p_); \
439 v += (d_); \
440 BUG_ON((v >> 31) != (v >> (n_-1))); \
441 *(s##n_ *)(p_) = (s##n_)v; \
442 } while (0)
443
444
445 static __always_inline
apply_reloc(int n,void * ptr,uintptr_t diff)446 void apply_reloc(int n, void *ptr, uintptr_t diff)
447 {
448 switch (n) {
449 case 1: apply_reloc_n(8, ptr, diff); break;
450 case 2: apply_reloc_n(16, ptr, diff); break;
451 case 4: apply_reloc_n(32, ptr, diff); break;
452 default: BUG();
453 }
454 }
455
456 static __always_inline
need_reloc(unsigned long offset,u8 * src,size_t src_len)457 bool need_reloc(unsigned long offset, u8 *src, size_t src_len)
458 {
459 u8 *target = src + offset;
460 /*
461 * If the target is inside the patched block, it's relative to the
462 * block itself and does not need relocation.
463 */
464 return (target < src || target > src + src_len);
465 }
466
__apply_relocation(u8 * buf,const u8 * const instr,size_t instrlen,u8 * repl,size_t repl_len)467 static void __apply_relocation(u8 *buf, const u8 * const instr, size_t instrlen, u8 *repl, size_t repl_len)
468 {
469 for (int next, i = 0; i < instrlen; i = next) {
470 struct insn insn;
471
472 if (WARN_ON_ONCE(insn_decode_kernel(&insn, &buf[i])))
473 return;
474
475 next = i + insn.length;
476
477 switch (insn.opcode.bytes[0]) {
478 case 0x0f:
479 if (insn.opcode.bytes[1] < 0x80 ||
480 insn.opcode.bytes[1] > 0x8f)
481 break;
482
483 fallthrough; /* Jcc.d32 */
484 case 0x70 ... 0x7f: /* Jcc.d8 */
485 case JMP8_INSN_OPCODE:
486 case JMP32_INSN_OPCODE:
487 case CALL_INSN_OPCODE:
488 if (need_reloc(next + insn.immediate.value, repl, repl_len)) {
489 apply_reloc(insn.immediate.nbytes,
490 buf + i + insn_offset_immediate(&insn),
491 repl - instr);
492 }
493
494 /*
495 * Where possible, convert JMP.d32 into JMP.d8.
496 */
497 if (insn.opcode.bytes[0] == JMP32_INSN_OPCODE) {
498 s32 imm = insn.immediate.value;
499 imm += repl - instr;
500 imm += JMP32_INSN_SIZE - JMP8_INSN_SIZE;
501 if ((imm >> 31) == (imm >> 7)) {
502 buf[i+0] = JMP8_INSN_OPCODE;
503 buf[i+1] = (s8)imm;
504
505 memset(&buf[i+2], INT3_INSN_OPCODE, insn.length - 2);
506 }
507 }
508 break;
509 }
510
511 if (insn_rip_relative(&insn)) {
512 if (need_reloc(next + insn.displacement.value, repl, repl_len)) {
513 apply_reloc(insn.displacement.nbytes,
514 buf + i + insn_offset_displacement(&insn),
515 repl - instr);
516 }
517 }
518 }
519 }
520
text_poke_apply_relocation(u8 * buf,const u8 * const instr,size_t instrlen,u8 * repl,size_t repl_len)521 void text_poke_apply_relocation(u8 *buf, const u8 * const instr, size_t instrlen, u8 *repl, size_t repl_len)
522 {
523 __apply_relocation(buf, instr, instrlen, repl, repl_len);
524 optimize_nops(instr, buf, instrlen);
525 }
526
527 /* Low-level backend functions usable from alternative code replacements. */
528 DEFINE_ASM_FUNC(nop_func, "", .entry.text);
529 EXPORT_SYMBOL_GPL(nop_func);
530
BUG_func(void)531 noinstr void BUG_func(void)
532 {
533 BUG();
534 }
535 EXPORT_SYMBOL(BUG_func);
536
537 #define CALL_RIP_REL_OPCODE 0xff
538 #define CALL_RIP_REL_MODRM 0x15
539
540 /*
541 * Rewrite the "call BUG_func" replacement to point to the target of the
542 * indirect pv_ops call "call *disp(%ip)".
543 */
alt_replace_call(u8 * instr,u8 * insn_buff,struct alt_instr * a)544 static unsigned int alt_replace_call(u8 *instr, u8 *insn_buff, struct alt_instr *a)
545 {
546 void *target, *bug = &BUG_func;
547 s32 disp;
548
549 if (a->replacementlen != 5 || insn_buff[0] != CALL_INSN_OPCODE) {
550 pr_err("ALT_FLAG_DIRECT_CALL set for a non-call replacement instruction\n");
551 BUG();
552 }
553
554 if (a->instrlen != 6 ||
555 instr[0] != CALL_RIP_REL_OPCODE ||
556 instr[1] != CALL_RIP_REL_MODRM) {
557 pr_err("ALT_FLAG_DIRECT_CALL set for unrecognized indirect call\n");
558 BUG();
559 }
560
561 /* Skip CALL_RIP_REL_OPCODE and CALL_RIP_REL_MODRM */
562 disp = *(s32 *)(instr + 2);
563 #ifdef CONFIG_X86_64
564 /* ff 15 00 00 00 00 call *0x0(%rip) */
565 /* target address is stored at "next instruction + disp". */
566 target = *(void **)(instr + a->instrlen + disp);
567 #else
568 /* ff 15 00 00 00 00 call *0x0 */
569 /* target address is stored at disp. */
570 target = *(void **)disp;
571 #endif
572 if (!target)
573 target = bug;
574
575 /* (BUG_func - .) + (target - BUG_func) := target - . */
576 *(s32 *)(insn_buff + 1) += target - bug;
577
578 if (target == &nop_func)
579 return 0;
580
581 return 5;
582 }
583
instr_va(struct alt_instr * i)584 static inline u8 * instr_va(struct alt_instr *i)
585 {
586 return (u8 *)&i->instr_offset + i->instr_offset;
587 }
588
589 struct patch_site {
590 u8 *instr;
591 struct alt_instr *alt;
592 u8 buff[MAX_PATCH_LEN];
593 u8 len;
594 };
595
analyze_patch_site(struct patch_site * ps,struct alt_instr * start,struct alt_instr * end)596 static struct alt_instr * __init_or_module analyze_patch_site(struct patch_site *ps,
597 struct alt_instr *start,
598 struct alt_instr *end)
599 {
600 struct alt_instr *alt = start;
601
602 ps->instr = instr_va(start);
603
604 /*
605 * In case of nested ALTERNATIVE()s the outer alternative might add
606 * more padding. To ensure consistent patching find the max padding for
607 * all alt_instr entries for this site (nested alternatives result in
608 * consecutive entries).
609 * Find the last alt_instr eligible for patching at the site.
610 */
611 for (; alt < end && instr_va(alt) == ps->instr; alt++) {
612 ps->len = max(ps->len, alt->instrlen);
613
614 BUG_ON(alt->cpuid >= (NCAPINTS + NBUGINTS) * 32);
615 /*
616 * Patch if either:
617 * - feature is present
618 * - feature not present but ALT_FLAG_NOT is set to mean,
619 * patch if feature is *NOT* present.
620 */
621 if (!boot_cpu_has(alt->cpuid) != !(alt->flags & ALT_FLAG_NOT))
622 ps->alt = alt;
623 }
624
625 BUG_ON(ps->len > sizeof(ps->buff));
626
627 return alt;
628 }
629
prep_patch_site(struct patch_site * ps)630 static void __init_or_module prep_patch_site(struct patch_site *ps)
631 {
632 struct alt_instr *alt = ps->alt;
633 u8 buff_sz;
634 u8 *repl;
635
636 if (!alt) {
637 /* Nothing to patch, use original instruction. */
638 memcpy(ps->buff, ps->instr, ps->len);
639 return;
640 }
641
642 repl = (u8 *)&alt->repl_offset + alt->repl_offset;
643 DPRINTK(ALT, "feat: %d*32+%d, old: (%pS (%px) len: %d), repl: (%px, len: %d) flags: 0x%x",
644 alt->cpuid >> 5, alt->cpuid & 0x1f,
645 ps->instr, ps->instr, ps->len,
646 repl, alt->replacementlen, alt->flags);
647
648 memcpy(ps->buff, repl, alt->replacementlen);
649 buff_sz = alt->replacementlen;
650
651 if (alt->flags & ALT_FLAG_DIRECT_CALL)
652 buff_sz = alt_replace_call(ps->instr, ps->buff, alt);
653
654 for (; buff_sz < ps->len; buff_sz++)
655 ps->buff[buff_sz] = 0x90;
656
657 __apply_relocation(ps->buff, ps->instr, ps->len, repl, alt->replacementlen);
658
659 DUMP_BYTES(ALT, ps->instr, ps->len, "%px: old_insn: ", ps->instr);
660 DUMP_BYTES(ALT, repl, alt->replacementlen, "%px: rpl_insn: ", repl);
661 DUMP_BYTES(ALT, ps->buff, ps->len, "%px: final_insn: ", ps->instr);
662 }
663
patch_site(struct patch_site * ps)664 static void __init_or_module patch_site(struct patch_site *ps)
665 {
666 optimize_nops(ps->instr, ps->buff, ps->len);
667 text_poke_early(ps->instr, ps->buff, ps->len);
668 }
669
670 /*
671 * Replace instructions with better alternatives for this CPU type. This runs
672 * before SMP is initialized to avoid SMP problems with self modifying code.
673 * This implies that asymmetric systems where APs have less capabilities than
674 * the boot processor are not handled. Tough. Make sure you disable such
675 * features by hand.
676 *
677 * Marked "noinline" to cause control flow change and thus insn cache
678 * to refetch changed I$ lines.
679 */
apply_alternatives(struct alt_instr * start,struct alt_instr * end)680 void __init_or_module noinline apply_alternatives(struct alt_instr *start,
681 struct alt_instr *end)
682 {
683 struct alt_instr *a;
684
685 DPRINTK(ALT, "alt table %px, -> %px", start, end);
686
687 /*
688 * KASAN_SHADOW_START is defined using
689 * cpu_feature_enabled(X86_FEATURE_LA57) and is therefore patched here.
690 * During the process, KASAN becomes confused seeing partial LA57
691 * conversion and triggers a false-positive out-of-bound report.
692 *
693 * Disable KASAN until the patching is complete.
694 */
695 kasan_disable_current();
696
697 /*
698 * The scan order should be from start to end. A later scanned
699 * alternative code can overwrite previously scanned alternative code.
700 * Some kernel functions (e.g. memcpy, memset, etc) use this order to
701 * patch code.
702 *
703 * So be careful if you want to change the scan order to any other
704 * order.
705 */
706 a = start;
707 while (a < end) {
708 struct patch_site ps = {
709 .alt = NULL,
710 .len = 0
711 };
712
713 a = analyze_patch_site(&ps, a, end);
714 prep_patch_site(&ps);
715 patch_site(&ps);
716 }
717
718 kasan_enable_current();
719 }
720
is_jcc32(struct insn * insn)721 static inline bool is_jcc32(struct insn *insn)
722 {
723 /* Jcc.d32 second opcode byte is in the range: 0x80-0x8f */
724 return insn->opcode.bytes[0] == 0x0f && (insn->opcode.bytes[1] & 0xf0) == 0x80;
725 }
726
727 #if defined(CONFIG_MITIGATION_RETPOLINE) && defined(CONFIG_OBJTOOL)
728
729 /*
730 * [CS]{,3} CALL/JMP *%\reg [INT3]*
731 */
emit_indirect(int op,int reg,u8 * bytes,int len)732 static int emit_indirect(int op, int reg, u8 *bytes, int len)
733 {
734 int cs = 0, bp = 0;
735 int i = 0;
736 u8 modrm;
737
738 /*
739 * Set @len to the excess bytes after writing the instruction.
740 */
741 len -= 2 + (reg >= 8);
742 WARN_ON_ONCE(len < 0);
743
744 switch (op) {
745 case CALL_INSN_OPCODE:
746 modrm = 0x10; /* Reg = 2; CALL r/m */
747 /*
748 * Additional NOP is better than prefix decode penalty.
749 */
750 if (len <= 3)
751 cs = len;
752 break;
753
754 case JMP32_INSN_OPCODE:
755 modrm = 0x20; /* Reg = 4; JMP r/m */
756 bp = len;
757 break;
758
759 default:
760 WARN_ON_ONCE(1);
761 return -1;
762 }
763
764 while (cs--)
765 bytes[i++] = 0x2e; /* CS-prefix */
766
767 if (reg >= 8) {
768 bytes[i++] = 0x41; /* REX.B prefix */
769 reg -= 8;
770 }
771
772 modrm |= 0xc0; /* Mod = 3 */
773 modrm += reg;
774
775 bytes[i++] = 0xff; /* opcode */
776 bytes[i++] = modrm;
777
778 while (bp--)
779 bytes[i++] = 0xcc; /* INT3 */
780
781 return i;
782 }
783
__emit_trampoline(void * addr,struct insn * insn,u8 * bytes,void * call_dest,void * jmp_dest)784 static int __emit_trampoline(void *addr, struct insn *insn, u8 *bytes,
785 void *call_dest, void *jmp_dest)
786 {
787 u8 op = insn->opcode.bytes[0];
788 int i = 0;
789
790 /*
791 * Clang does 'weird' Jcc __x86_indirect_thunk_r11 conditional
792 * tail-calls. Deal with them.
793 */
794 if (is_jcc32(insn)) {
795 bytes[i++] = op;
796 op = insn->opcode.bytes[1];
797 goto clang_jcc;
798 }
799
800 if (insn->length == 6)
801 bytes[i++] = 0x2e; /* CS-prefix */
802
803 switch (op) {
804 case CALL_INSN_OPCODE:
805 __text_gen_insn(bytes+i, op, addr+i,
806 call_dest,
807 CALL_INSN_SIZE);
808 i += CALL_INSN_SIZE;
809 break;
810
811 case JMP32_INSN_OPCODE:
812 clang_jcc:
813 __text_gen_insn(bytes+i, op, addr+i,
814 jmp_dest,
815 JMP32_INSN_SIZE);
816 i += JMP32_INSN_SIZE;
817 break;
818
819 default:
820 WARN(1, "%pS %px %*ph\n", addr, addr, 6, addr);
821 return -1;
822 }
823
824 WARN_ON_ONCE(i != insn->length);
825
826 return i;
827 }
828
emit_call_track_retpoline(void * addr,struct insn * insn,int reg,u8 * bytes)829 static int emit_call_track_retpoline(void *addr, struct insn *insn, int reg, u8 *bytes)
830 {
831 return __emit_trampoline(addr, insn, bytes,
832 __x86_indirect_call_thunk_array[reg],
833 __x86_indirect_jump_thunk_array[reg]);
834 }
835
836 #ifdef CONFIG_MITIGATION_ITS
emit_its_trampoline(void * addr,struct insn * insn,int reg,u8 * bytes)837 static int emit_its_trampoline(void *addr, struct insn *insn, int reg, u8 *bytes)
838 {
839 u8 *thunk = __x86_indirect_its_thunk_array[reg];
840 u8 *tmp = its_allocate_thunk(reg);
841
842 if (tmp)
843 thunk = tmp;
844
845 return __emit_trampoline(addr, insn, bytes, thunk, thunk);
846 }
847
848 /* Check if an indirect branch is at ITS-unsafe address */
cpu_wants_indirect_its_thunk_at(unsigned long addr,int reg)849 static bool cpu_wants_indirect_its_thunk_at(unsigned long addr, int reg)
850 {
851 if (!cpu_feature_enabled(X86_FEATURE_INDIRECT_THUNK_ITS))
852 return false;
853
854 /* Indirect branch opcode is 2 or 3 bytes depending on reg */
855 addr += 1 + reg / 8;
856
857 /* Lower-half of the cacheline? */
858 return !(addr & 0x20);
859 }
860 #else /* CONFIG_MITIGATION_ITS */
861
862 #ifdef CONFIG_FINEIBT
cpu_wants_indirect_its_thunk_at(unsigned long addr,int reg)863 static bool cpu_wants_indirect_its_thunk_at(unsigned long addr, int reg)
864 {
865 return false;
866 }
867 #endif
868
869 #endif /* CONFIG_MITIGATION_ITS */
870
871 /*
872 * Rewrite the compiler generated retpoline thunk calls.
873 *
874 * For spectre_v2=off (!X86_FEATURE_RETPOLINE), rewrite them into immediate
875 * indirect instructions, avoiding the extra indirection.
876 *
877 * For example, convert:
878 *
879 * CALL __x86_indirect_thunk_\reg
880 *
881 * into:
882 *
883 * CALL *%\reg
884 *
885 * It also tries to inline spectre_v2=retpoline,lfence when size permits.
886 */
patch_retpoline(void * addr,struct insn * insn,u8 * bytes)887 static int patch_retpoline(void *addr, struct insn *insn, u8 *bytes)
888 {
889 retpoline_thunk_t *target;
890 int reg, ret, i = 0;
891 u8 op, cc;
892
893 target = addr + insn->length + insn->immediate.value;
894 reg = target - __x86_indirect_thunk_array;
895
896 if (WARN_ON_ONCE(reg & ~0xf))
897 return -1;
898
899 /* If anyone ever does: CALL/JMP *%rsp, we're in deep trouble. */
900 BUG_ON(reg == 4);
901
902 if (cpu_feature_enabled(X86_FEATURE_RETPOLINE) &&
903 !cpu_feature_enabled(X86_FEATURE_RETPOLINE_LFENCE)) {
904 if (cpu_feature_enabled(X86_FEATURE_CALL_DEPTH))
905 return emit_call_track_retpoline(addr, insn, reg, bytes);
906
907 return -1;
908 }
909
910 op = insn->opcode.bytes[0];
911
912 /*
913 * Convert:
914 *
915 * Jcc.d32 __x86_indirect_thunk_\reg
916 *
917 * into:
918 *
919 * Jncc.d8 1f
920 * [ LFENCE ]
921 * JMP *%\reg
922 * [ NOP ]
923 * 1:
924 */
925 if (is_jcc32(insn)) {
926 cc = insn->opcode.bytes[1] & 0xf;
927 cc ^= 1; /* invert condition */
928
929 bytes[i++] = 0x70 + cc; /* Jcc.d8 */
930 bytes[i++] = insn->length - 2; /* sizeof(Jcc.d8) == 2 */
931
932 /* Continue as if: JMP.d32 __x86_indirect_thunk_\reg */
933 op = JMP32_INSN_OPCODE;
934 }
935
936 /*
937 * For RETPOLINE_LFENCE: prepend the indirect CALL/JMP with an LFENCE.
938 */
939 if (cpu_feature_enabled(X86_FEATURE_RETPOLINE_LFENCE)) {
940 bytes[i++] = 0x0f;
941 bytes[i++] = 0xae;
942 bytes[i++] = 0xe8; /* LFENCE */
943 }
944
945 #ifdef CONFIG_MITIGATION_ITS
946 /*
947 * Check if the address of last byte of emitted-indirect is in
948 * lower-half of the cacheline. Such branches need ITS mitigation.
949 */
950 if (cpu_wants_indirect_its_thunk_at((unsigned long)addr + i, reg))
951 return emit_its_trampoline(addr, insn, reg, bytes);
952 #endif
953
954 ret = emit_indirect(op, reg, bytes + i, insn->length - i);
955 if (ret < 0)
956 return ret;
957 i += ret;
958
959 for (; i < insn->length;)
960 bytes[i++] = BYTES_NOP1;
961
962 return i;
963 }
964
965 /*
966 * Generated by 'objtool --retpoline'.
967 */
apply_retpolines(s32 * start,s32 * end)968 void __init_or_module noinline apply_retpolines(s32 *start, s32 *end)
969 {
970 s32 *s;
971
972 for (s = start; s < end; s++) {
973 void *addr = (void *)s + *s;
974 struct insn insn;
975 int len, ret;
976 u8 bytes[16];
977 u8 op1, op2;
978 u8 *dest;
979
980 ret = insn_decode_kernel(&insn, addr);
981 if (WARN_ON_ONCE(ret < 0))
982 continue;
983
984 op1 = insn.opcode.bytes[0];
985 op2 = insn.opcode.bytes[1];
986
987 switch (op1) {
988 case 0x70 ... 0x7f: /* Jcc.d8 */
989 /* See cfi_paranoid. */
990 WARN_ON_ONCE(cfi_mode != CFI_FINEIBT);
991 continue;
992
993 case CALL_INSN_OPCODE:
994 case JMP32_INSN_OPCODE:
995 /* Check for cfi_paranoid + ITS */
996 dest = addr + insn.length + insn.immediate.value;
997 if (dest[-1] == 0xd6 && (dest[0] & 0xf0) == 0x70) {
998 WARN_ON_ONCE(cfi_mode != CFI_FINEIBT);
999 continue;
1000 }
1001 break;
1002
1003 case 0x0f: /* escape */
1004 if (op2 >= 0x80 && op2 <= 0x8f)
1005 break;
1006 fallthrough;
1007 default:
1008 WARN_ON_ONCE(1);
1009 continue;
1010 }
1011
1012 DPRINTK(RETPOLINE, "retpoline at: %pS (%px) len: %d to: %pS",
1013 addr, addr, insn.length,
1014 addr + insn.length + insn.immediate.value);
1015
1016 len = patch_retpoline(addr, &insn, bytes);
1017 if (len == insn.length) {
1018 optimize_nops(addr, bytes, len);
1019 DUMP_BYTES(RETPOLINE, ((u8*)addr), len, "%px: orig: ", addr);
1020 DUMP_BYTES(RETPOLINE, ((u8*)bytes), len, "%px: repl: ", addr);
1021 text_poke_early(addr, bytes, len);
1022 }
1023 }
1024 }
1025
1026 #ifdef CONFIG_MITIGATION_RETHUNK
1027
cpu_wants_rethunk(void)1028 bool cpu_wants_rethunk(void)
1029 {
1030 return cpu_feature_enabled(X86_FEATURE_RETHUNK);
1031 }
1032
cpu_wants_rethunk_at(void * addr)1033 bool cpu_wants_rethunk_at(void *addr)
1034 {
1035 if (!cpu_feature_enabled(X86_FEATURE_RETHUNK))
1036 return false;
1037 if (x86_return_thunk != its_return_thunk)
1038 return true;
1039
1040 return !((unsigned long)addr & 0x20);
1041 }
1042
1043 /*
1044 * Rewrite the compiler generated return thunk tail-calls.
1045 *
1046 * For example, convert:
1047 *
1048 * JMP __x86_return_thunk
1049 *
1050 * into:
1051 *
1052 * RET
1053 */
patch_return(void * addr,struct insn * insn,u8 * bytes)1054 static int patch_return(void *addr, struct insn *insn, u8 *bytes)
1055 {
1056 int i = 0;
1057
1058 /* Patch the custom return thunks... */
1059 if (cpu_wants_rethunk_at(addr)) {
1060 i = JMP32_INSN_SIZE;
1061 __text_gen_insn(bytes, JMP32_INSN_OPCODE, addr, x86_return_thunk, i);
1062 } else {
1063 /* ... or patch them out if not needed. */
1064 bytes[i++] = RET_INSN_OPCODE;
1065 }
1066
1067 for (; i < insn->length;)
1068 bytes[i++] = INT3_INSN_OPCODE;
1069 return i;
1070 }
1071
apply_returns(s32 * start,s32 * end)1072 void __init_or_module noinline apply_returns(s32 *start, s32 *end)
1073 {
1074 s32 *s;
1075
1076 if (cpu_wants_rethunk())
1077 static_call_force_reinit();
1078
1079 for (s = start; s < end; s++) {
1080 void *dest = NULL, *addr = (void *)s + *s;
1081 struct insn insn;
1082 int len, ret;
1083 u8 bytes[16];
1084 u8 op;
1085
1086 ret = insn_decode_kernel(&insn, addr);
1087 if (WARN_ON_ONCE(ret < 0))
1088 continue;
1089
1090 op = insn.opcode.bytes[0];
1091 if (op == JMP32_INSN_OPCODE)
1092 dest = addr + insn.length + insn.immediate.value;
1093
1094 if (__static_call_fixup(addr, op, dest) ||
1095 WARN_ONCE(dest != &__x86_return_thunk,
1096 "missing return thunk: %pS-%pS: %*ph",
1097 addr, dest, 5, addr))
1098 continue;
1099
1100 DPRINTK(RET, "return thunk at: %pS (%px) len: %d to: %pS",
1101 addr, addr, insn.length,
1102 addr + insn.length + insn.immediate.value);
1103
1104 len = patch_return(addr, &insn, bytes);
1105 if (len == insn.length) {
1106 DUMP_BYTES(RET, ((u8*)addr), len, "%px: orig: ", addr);
1107 DUMP_BYTES(RET, ((u8*)bytes), len, "%px: repl: ", addr);
1108 text_poke_early(addr, bytes, len);
1109 }
1110 }
1111 }
1112 #else /* !CONFIG_MITIGATION_RETHUNK: */
apply_returns(s32 * start,s32 * end)1113 void __init_or_module noinline apply_returns(s32 *start, s32 *end) { }
1114 #endif /* !CONFIG_MITIGATION_RETHUNK */
1115
1116 #else /* !CONFIG_MITIGATION_RETPOLINE || !CONFIG_OBJTOOL */
1117
apply_retpolines(s32 * start,s32 * end)1118 void __init_or_module noinline apply_retpolines(s32 *start, s32 *end) { }
apply_returns(s32 * start,s32 * end)1119 void __init_or_module noinline apply_returns(s32 *start, s32 *end) { }
1120
1121 #endif /* !CONFIG_MITIGATION_RETPOLINE || !CONFIG_OBJTOOL */
1122
1123 #ifdef CONFIG_X86_KERNEL_IBT
1124
is_endbr(u32 * val)1125 __noendbr bool is_endbr(u32 *val)
1126 {
1127 u32 endbr;
1128
1129 __get_kernel_nofault(&endbr, val, u32, Efault);
1130 return __is_endbr(endbr);
1131
1132 Efault:
1133 return false;
1134 }
1135
1136 #ifdef CONFIG_FINEIBT
1137
exact_endbr(u32 * val)1138 static __noendbr bool exact_endbr(u32 *val)
1139 {
1140 u32 endbr;
1141
1142 __get_kernel_nofault(&endbr, val, u32, Efault);
1143 return endbr == gen_endbr();
1144
1145 Efault:
1146 return false;
1147 }
1148
1149 #endif
1150
1151 static void poison_cfi(void *addr);
1152
poison_endbr(void * addr)1153 static void __init_or_module poison_endbr(void *addr)
1154 {
1155 u32 poison = gen_endbr_poison();
1156
1157 if (WARN_ON_ONCE(!is_endbr(addr)))
1158 return;
1159
1160 DPRINTK(ENDBR, "ENDBR at: %pS (%px)", addr, addr);
1161
1162 /*
1163 * When we have IBT, the lack of ENDBR will trigger #CP
1164 */
1165 DUMP_BYTES(ENDBR, ((u8*)addr), 4, "%px: orig: ", addr);
1166 DUMP_BYTES(ENDBR, ((u8*)&poison), 4, "%px: repl: ", addr);
1167 text_poke_early(addr, &poison, 4);
1168 }
1169
1170 /*
1171 * Generated by: objtool --ibt
1172 *
1173 * Seal the functions for indirect calls by clobbering the ENDBR instructions
1174 * and the kCFI hash value.
1175 */
apply_seal_endbr(s32 * start,s32 * end)1176 void __init_or_module noinline apply_seal_endbr(s32 *start, s32 *end)
1177 {
1178 s32 *s;
1179
1180 for (s = start; s < end; s++) {
1181 void *addr = (void *)s + *s;
1182
1183 poison_endbr(addr);
1184 if (IS_ENABLED(CONFIG_FINEIBT))
1185 poison_cfi(addr - CFI_OFFSET);
1186 }
1187 }
1188
1189 #else /* !CONFIG_X86_KERNEL_IBT: */
1190
apply_seal_endbr(s32 * start,s32 * end)1191 void __init_or_module apply_seal_endbr(s32 *start, s32 *end) { }
1192
1193 #endif /* !CONFIG_X86_KERNEL_IBT */
1194
1195 #ifdef CONFIG_CFI_AUTO_DEFAULT
1196 # define __CFI_DEFAULT CFI_AUTO
1197 #elif defined(CONFIG_CFI)
1198 # define __CFI_DEFAULT CFI_KCFI
1199 #else
1200 # define __CFI_DEFAULT CFI_OFF
1201 #endif
1202
1203 enum cfi_mode cfi_mode __ro_after_init = __CFI_DEFAULT;
1204 static bool cfi_debug __ro_after_init;
1205
1206 #ifdef CONFIG_FINEIBT_BHI
1207 bool cfi_bhi __ro_after_init = false;
1208 #endif
1209
1210 #ifdef CONFIG_CFI
cfi_get_func_hash(void * func)1211 u32 cfi_get_func_hash(void *func)
1212 {
1213 u32 hash;
1214
1215 func -= cfi_get_offset();
1216 switch (cfi_mode) {
1217 case CFI_FINEIBT:
1218 func += 7;
1219 break;
1220 case CFI_KCFI:
1221 func += 1;
1222 break;
1223 default:
1224 return 0;
1225 }
1226
1227 if (get_kernel_nofault(hash, func))
1228 return 0;
1229
1230 return hash;
1231 }
1232
cfi_get_func_arity(void * func)1233 int cfi_get_func_arity(void *func)
1234 {
1235 bhi_thunk *target;
1236 s32 disp;
1237
1238 if (cfi_mode != CFI_FINEIBT && !cfi_bhi)
1239 return 0;
1240
1241 if (get_kernel_nofault(disp, func - 4))
1242 return 0;
1243
1244 target = func + disp;
1245 return target - __bhi_args;
1246 }
1247 #endif
1248
1249 #ifdef CONFIG_FINEIBT
1250
1251 static bool cfi_rand __ro_after_init = true;
1252 static u32 cfi_seed __ro_after_init;
1253
1254 /*
1255 * Re-hash the CFI hash with a boot-time seed while making sure the result is
1256 * not a valid ENDBR instruction.
1257 */
cfi_rehash(u32 hash)1258 static u32 cfi_rehash(u32 hash)
1259 {
1260 hash ^= cfi_seed;
1261 while (unlikely(__is_endbr(hash) || __is_endbr(-hash))) {
1262 bool lsb = hash & 1;
1263 hash >>= 1;
1264 if (lsb)
1265 hash ^= 0x80200003;
1266 }
1267 return hash;
1268 }
1269
cfi_parse_cmdline(char * str)1270 static __init int cfi_parse_cmdline(char *str)
1271 {
1272 if (!str)
1273 return -EINVAL;
1274
1275 while (str) {
1276 char *next = strchr(str, ',');
1277 if (next) {
1278 *next = 0;
1279 next++;
1280 }
1281
1282 if (!strcmp(str, "auto")) {
1283 cfi_mode = CFI_AUTO;
1284 } else if (!strcmp(str, "off")) {
1285 cfi_mode = CFI_OFF;
1286 cfi_rand = false;
1287 } else if (!strcmp(str, "debug")) {
1288 cfi_debug = true;
1289 } else if (!strcmp(str, "kcfi")) {
1290 cfi_mode = CFI_KCFI;
1291 } else if (!strcmp(str, "fineibt")) {
1292 cfi_mode = CFI_FINEIBT;
1293 } else if (!strcmp(str, "norand")) {
1294 cfi_rand = false;
1295 } else if (!strcmp(str, "warn")) {
1296 pr_alert("CFI: mismatch non-fatal!\n");
1297 cfi_warn = true;
1298 } else if (!strcmp(str, "paranoid")) {
1299 if (cfi_mode == CFI_FINEIBT) {
1300 cfi_paranoid = true;
1301 } else {
1302 pr_err("CFI: ignoring paranoid; depends on fineibt.\n");
1303 }
1304 } else if (!strcmp(str, "bhi")) {
1305 #ifdef CONFIG_FINEIBT_BHI
1306 if (cfi_mode == CFI_FINEIBT) {
1307 cfi_bhi = true;
1308 } else {
1309 pr_err("CFI: ignoring bhi; depends on fineibt.\n");
1310 }
1311 #else
1312 pr_err("CFI: ignoring bhi; depends on FINEIBT_BHI=y.\n");
1313 #endif
1314 } else {
1315 pr_err("CFI: Ignoring unknown option (%s).", str);
1316 }
1317
1318 str = next;
1319 }
1320
1321 return 0;
1322 }
1323 early_param("cfi", cfi_parse_cmdline);
1324
1325 /*
1326 * kCFI FineIBT
1327 *
1328 * __cfi_\func: __cfi_\func:
1329 * movl $0x12345678,%eax // 5 endbr64 // 4
1330 * nop subl $0x12345678,%eax // 5
1331 * nop jne.d32,pn \func+3 // 7
1332 * nop
1333 * nop
1334 * nop
1335 * nop
1336 * nop
1337 * nop
1338 * nop
1339 * nop
1340 * nop
1341 * \func: \func:
1342 * endbr64 nopl -42(%rax)
1343 *
1344 *
1345 * caller: caller:
1346 * movl $(-0x12345678),%r10d // 6 movl $0x12345678,%eax // 5
1347 * addl $-15(%r11),%r10d // 4 lea -0x10(%r11),%r11 // 4
1348 * je 1f // 2 nop5 // 5
1349 * ud2 // 2
1350 * 1: cs call __x86_indirect_thunk_r11 // 6 call *%r11; nop3; // 6
1351 *
1352 *
1353 * Notably, the FineIBT sequences are crafted such that branches are presumed
1354 * non-taken. This is based on Agner Fog's optimization manual, which states:
1355 *
1356 * "Make conditional jumps most often not taken: The efficiency and throughput
1357 * for not-taken branches is better than for taken branches on most
1358 * processors. Therefore, it is good to place the most frequent branch first"
1359 */
1360
1361 /*
1362 * <fineibt_preamble_start>:
1363 * 0: f3 0f 1e fa endbr64
1364 * 4: 2d 78 56 34 12 sub $0x12345678, %eax
1365 * 9: 2e 0f 85 03 00 00 00 jne,pn 13 <fineibt_preamble_start+0x13>
1366 * 10: 0f 1f 40 d6 nopl -0x2a(%rax)
1367 *
1368 * Note that the JNE target is the 0xD6 byte inside the NOPL, this decodes as
1369 * UDB on x86_64 and raises #UD.
1370 */
1371 asm( ".pushsection .rodata \n"
1372 "fineibt_preamble_start: \n"
1373 " endbr64 \n"
1374 " subl $0x12345678, %eax \n"
1375 "fineibt_preamble_bhi: \n"
1376 " cs jne.d32 fineibt_preamble_start+0x13 \n"
1377 "#fineibt_func: \n"
1378 " nopl -42(%rax) \n"
1379 "fineibt_preamble_end: \n"
1380 ".popsection\n"
1381 );
1382
1383 extern u8 fineibt_preamble_start[];
1384 extern u8 fineibt_preamble_bhi[];
1385 extern u8 fineibt_preamble_end[];
1386
1387 #define fineibt_preamble_size (fineibt_preamble_end - fineibt_preamble_start)
1388 #define fineibt_preamble_bhi (fineibt_preamble_bhi - fineibt_preamble_start)
1389 #define fineibt_preamble_ud 0x13
1390 #define fineibt_preamble_hash 5
1391
1392 #define fineibt_prefix_size (fineibt_preamble_size - ENDBR_INSN_SIZE)
1393
1394 /*
1395 * <fineibt_caller_start>:
1396 * 0: b8 78 56 34 12 mov $0x12345678, %eax
1397 * 5: 4d 8d 5b f0 lea -0x10(%r11), %r11
1398 * 9: 0f 1f 44 00 00 nopl 0x0(%rax,%rax,1)
1399 */
1400 asm( ".pushsection .rodata \n"
1401 "fineibt_caller_start: \n"
1402 " movl $0x12345678, %eax \n"
1403 " lea -0x10(%r11), %r11 \n"
1404 ASM_NOP5
1405 "fineibt_caller_end: \n"
1406 ".popsection \n"
1407 );
1408
1409 extern u8 fineibt_caller_start[];
1410 extern u8 fineibt_caller_end[];
1411
1412 #define fineibt_caller_size (fineibt_caller_end - fineibt_caller_start)
1413 #define fineibt_caller_hash 1
1414
1415 #define fineibt_caller_jmp (fineibt_caller_size - 2)
1416
1417 /*
1418 * Since FineIBT does hash validation on the callee side it is prone to
1419 * circumvention attacks where a 'naked' ENDBR instruction exists that
1420 * is not part of the fineibt_preamble sequence.
1421 *
1422 * Notably the x86 entry points must be ENDBR and equally cannot be
1423 * fineibt_preamble.
1424 *
1425 * The fineibt_paranoid caller sequence adds additional caller side
1426 * hash validation. This stops such circumvention attacks dead, but at the cost
1427 * of adding a load.
1428 *
1429 * <fineibt_paranoid_start>:
1430 * 0: b8 78 56 34 12 mov $0x12345678, %eax
1431 * 5: 41 3b 43 f5 cmp -0x11(%r11), %eax
1432 * 9: 2e 4d 8d 5b <f0> cs lea -0x10(%r11), %r11
1433 * e: 75 fd jne d <fineibt_paranoid_start+0xd>
1434 * 10: 41 ff d3 call *%r11
1435 * 13: 90 nop
1436 *
1437 * Notably LEA does not modify flags and can be reordered with the CMP,
1438 * avoiding a dependency. Again, using a non-taken (backwards) branch
1439 * for the failure case, abusing LEA's immediate 0xf0 as LOCK prefix for the
1440 * Jcc.d8, causing #UD.
1441 */
1442 asm( ".pushsection .rodata \n"
1443 "fineibt_paranoid_start: \n"
1444 " mov $0x12345678, %eax \n"
1445 " cmpl -11(%r11), %eax \n"
1446 " cs lea -0x10(%r11), %r11 \n"
1447 "#fineibt_caller_size: \n"
1448 " jne fineibt_paranoid_start+0xd \n"
1449 "fineibt_paranoid_ind: \n"
1450 " cs call *%r11 \n"
1451 "fineibt_paranoid_end: \n"
1452 ".popsection \n"
1453 );
1454
1455 extern u8 fineibt_paranoid_start[];
1456 extern u8 fineibt_paranoid_ind[];
1457 extern u8 fineibt_paranoid_end[];
1458
1459 #define fineibt_paranoid_size (fineibt_paranoid_end - fineibt_paranoid_start)
1460 #define fineibt_paranoid_ind (fineibt_paranoid_ind - fineibt_paranoid_start)
1461 #define fineibt_paranoid_ud 0xd
1462
decode_preamble_hash(void * addr,int * reg)1463 static u32 decode_preamble_hash(void *addr, int *reg)
1464 {
1465 u8 *p = addr;
1466
1467 /* b8+reg 78 56 34 12 movl $0x12345678,\reg */
1468 if (p[0] >= 0xb8 && p[0] < 0xc0) {
1469 if (reg)
1470 *reg = p[0] - 0xb8;
1471 return *(u32 *)(addr + 1);
1472 }
1473
1474 return 0; /* invalid hash value */
1475 }
1476
decode_caller_hash(void * addr)1477 static u32 decode_caller_hash(void *addr)
1478 {
1479 u8 *p = addr;
1480
1481 /* 41 ba 88 a9 cb ed mov $(-0x12345678),%r10d */
1482 if (p[0] == 0x41 && p[1] == 0xba)
1483 return -*(u32 *)(addr + 2);
1484
1485 /* e8 0c 88 a9 cb ed jmp.d8 +12 */
1486 if (p[0] == JMP8_INSN_OPCODE && p[1] == fineibt_caller_jmp)
1487 return -*(u32 *)(addr + 2);
1488
1489 return 0; /* invalid hash value */
1490 }
1491
1492 /* .retpoline_sites */
cfi_disable_callers(s32 * start,s32 * end)1493 static int cfi_disable_callers(s32 *start, s32 *end)
1494 {
1495 /*
1496 * Disable kCFI by patching in a JMP.d8, this leaves the hash immediate
1497 * in tact for later usage. Also see decode_caller_hash() and
1498 * cfi_rewrite_callers().
1499 */
1500 const u8 jmp[] = { JMP8_INSN_OPCODE, fineibt_caller_jmp };
1501 s32 *s;
1502
1503 for (s = start; s < end; s++) {
1504 void *addr = (void *)s + *s;
1505 u32 hash;
1506
1507 addr -= fineibt_caller_size;
1508 hash = decode_caller_hash(addr);
1509 if (!hash) /* nocfi callers */
1510 continue;
1511
1512 text_poke_early(addr, jmp, 2);
1513 }
1514
1515 return 0;
1516 }
1517
cfi_enable_callers(s32 * start,s32 * end)1518 static int cfi_enable_callers(s32 *start, s32 *end)
1519 {
1520 /*
1521 * Re-enable kCFI, undo what cfi_disable_callers() did.
1522 */
1523 const u8 mov[] = { 0x41, 0xba };
1524 s32 *s;
1525
1526 for (s = start; s < end; s++) {
1527 void *addr = (void *)s + *s;
1528 u32 hash;
1529
1530 addr -= fineibt_caller_size;
1531 hash = decode_caller_hash(addr);
1532 if (!hash) /* nocfi callers */
1533 continue;
1534
1535 text_poke_early(addr, mov, 2);
1536 }
1537
1538 return 0;
1539 }
1540
1541 /* .cfi_sites */
cfi_rand_preamble(s32 * start,s32 * end)1542 static int cfi_rand_preamble(s32 *start, s32 *end)
1543 {
1544 s32 *s;
1545
1546 for (s = start; s < end; s++) {
1547 void *addr = (void *)s + *s;
1548 u32 hash;
1549
1550 hash = decode_preamble_hash(addr, NULL);
1551 if (WARN(!hash, "no CFI hash found at: %pS %px %*ph\n",
1552 addr, addr, 5, addr))
1553 return -EINVAL;
1554
1555 hash = cfi_rehash(hash);
1556 text_poke_early(addr + 1, &hash, 4);
1557 }
1558
1559 return 0;
1560 }
1561
1562 /*
1563 * Inline the bhi-arity 1 case:
1564 *
1565 * __cfi_foo:
1566 * 0: f3 0f 1e fa endbr64
1567 * 4: 2d 78 56 34 12 sub $0x12345678, %eax
1568 * 9: 49 0f 45 fa cmovne %rax, %rdi
1569 * d: 2e 75 03 jne,pn foo+0x3
1570 *
1571 * foo:
1572 * 10: 0f 1f 40 <d6> nopl -42(%rax)
1573 *
1574 * Notably, this scheme is incompatible with permissive CFI
1575 * because the CMOVcc is unconditional and RDI will have been
1576 * clobbered.
1577 */
1578 asm( ".pushsection .rodata \n"
1579 "fineibt_bhi1_start: \n"
1580 " cmovne %rax, %rdi \n"
1581 " cs jne fineibt_bhi1_func + 0x3 \n"
1582 "fineibt_bhi1_func: \n"
1583 " nopl -42(%rax) \n"
1584 "fineibt_bhi1_end: \n"
1585 ".popsection \n"
1586 );
1587
1588 extern u8 fineibt_bhi1_start[];
1589 extern u8 fineibt_bhi1_end[];
1590
1591 #define fineibt_bhi1_size (fineibt_bhi1_end - fineibt_bhi1_start)
1592
cfi_fineibt_bhi_preamble(void * addr,int arity)1593 static void cfi_fineibt_bhi_preamble(void *addr, int arity)
1594 {
1595 u8 bytes[MAX_INSN_SIZE];
1596
1597 if (!arity)
1598 return;
1599
1600 if (!cfi_warn && arity == 1) {
1601 text_poke_early(addr + fineibt_preamble_bhi,
1602 fineibt_bhi1_start, fineibt_bhi1_size);
1603 return;
1604 }
1605
1606 /*
1607 * Replace the bytes at fineibt_preamble_bhi with a CALL instruction
1608 * that lines up exactly with the end of the preamble, such that the
1609 * return address will be foo+0.
1610 *
1611 * __cfi_foo:
1612 * 0: f3 0f 1e fa endbr64
1613 * 4: 2d 78 56 34 12 sub $0x12345678, %eax
1614 * 9: 2e 2e e8 DD DD DD DD cs cs call __bhi_args[arity]
1615 */
1616 bytes[0] = 0x2e;
1617 bytes[1] = 0x2e;
1618 __text_gen_insn(bytes + 2, CALL_INSN_OPCODE,
1619 addr + fineibt_preamble_bhi + 2,
1620 __bhi_args[arity], CALL_INSN_SIZE);
1621
1622 text_poke_early(addr + fineibt_preamble_bhi, bytes, 7);
1623 }
1624
cfi_rewrite_preamble(s32 * start,s32 * end)1625 static int cfi_rewrite_preamble(s32 *start, s32 *end)
1626 {
1627 s32 *s;
1628
1629 for (s = start; s < end; s++) {
1630 void *addr = (void *)s + *s;
1631 int arity;
1632 u32 hash;
1633
1634 /*
1635 * When the function doesn't start with ENDBR the compiler will
1636 * have determined there are no indirect calls to it and we
1637 * don't need no CFI either.
1638 */
1639 if (!is_endbr(addr + CFI_OFFSET))
1640 continue;
1641
1642 hash = decode_preamble_hash(addr, &arity);
1643 if (WARN(!hash, "no CFI hash found at: %pS %px %*ph\n",
1644 addr, addr, 5, addr))
1645 return -EINVAL;
1646
1647 /*
1648 * FineIBT relies on being at func-16, so if the preamble is
1649 * actually larger than that, place it the tail end.
1650 *
1651 * NOTE: this is possible with things like DEBUG_CALL_THUNKS
1652 * and DEBUG_FORCE_FUNCTION_ALIGN_64B.
1653 */
1654 addr += CFI_OFFSET - fineibt_prefix_size;
1655
1656 text_poke_early(addr, fineibt_preamble_start, fineibt_preamble_size);
1657 WARN_ON(*(u32 *)(addr + fineibt_preamble_hash) != 0x12345678);
1658 text_poke_early(addr + fineibt_preamble_hash, &hash, 4);
1659
1660 WARN_ONCE(!IS_ENABLED(CONFIG_FINEIBT_BHI) && arity,
1661 "kCFI preamble has wrong register at: %pS %*ph\n",
1662 addr, 5, addr);
1663
1664 if (cfi_bhi)
1665 cfi_fineibt_bhi_preamble(addr, arity);
1666 }
1667
1668 return 0;
1669 }
1670
cfi_rewrite_endbr(s32 * start,s32 * end)1671 static void cfi_rewrite_endbr(s32 *start, s32 *end)
1672 {
1673 s32 *s;
1674
1675 for (s = start; s < end; s++) {
1676 void *addr = (void *)s + *s;
1677
1678 if (!exact_endbr(addr + CFI_OFFSET))
1679 continue;
1680
1681 poison_endbr(addr + CFI_OFFSET);
1682 }
1683 }
1684
1685 /* .retpoline_sites */
cfi_rand_callers(s32 * start,s32 * end)1686 static int cfi_rand_callers(s32 *start, s32 *end)
1687 {
1688 s32 *s;
1689
1690 for (s = start; s < end; s++) {
1691 void *addr = (void *)s + *s;
1692 u32 hash;
1693
1694 addr -= fineibt_caller_size;
1695 hash = decode_caller_hash(addr);
1696 if (hash) {
1697 hash = -cfi_rehash(hash);
1698 text_poke_early(addr + 2, &hash, 4);
1699 }
1700 }
1701
1702 return 0;
1703 }
1704
emit_paranoid_trampoline(void * addr,struct insn * insn,int reg,u8 * bytes)1705 static int emit_paranoid_trampoline(void *addr, struct insn *insn, int reg, u8 *bytes)
1706 {
1707 u8 *thunk = (void *)__x86_indirect_its_thunk_array[reg] - 2;
1708
1709 #ifdef CONFIG_MITIGATION_ITS
1710 u8 *tmp = its_allocate_thunk(reg);
1711 if (tmp)
1712 thunk = tmp;
1713 #endif
1714
1715 return __emit_trampoline(addr, insn, bytes, thunk, thunk);
1716 }
1717
cfi_rewrite_callers(s32 * start,s32 * end)1718 static int cfi_rewrite_callers(s32 *start, s32 *end)
1719 {
1720 s32 *s;
1721
1722 for (s = start; s < end; s++) {
1723 void *addr = (void *)s + *s;
1724 struct insn insn;
1725 u8 bytes[20];
1726 u32 hash;
1727 int ret;
1728 u8 op;
1729
1730 addr -= fineibt_caller_size;
1731 hash = decode_caller_hash(addr);
1732 if (!hash)
1733 continue;
1734
1735 if (!cfi_paranoid) {
1736 text_poke_early(addr, fineibt_caller_start, fineibt_caller_size);
1737 WARN_ON(*(u32 *)(addr + fineibt_caller_hash) != 0x12345678);
1738 text_poke_early(addr + fineibt_caller_hash, &hash, 4);
1739 /* rely on apply_retpolines() */
1740 continue;
1741 }
1742
1743 /* cfi_paranoid */
1744 ret = insn_decode_kernel(&insn, addr + fineibt_caller_size);
1745 if (WARN_ON_ONCE(ret < 0))
1746 continue;
1747
1748 op = insn.opcode.bytes[0];
1749 if (op != CALL_INSN_OPCODE && op != JMP32_INSN_OPCODE) {
1750 WARN_ON_ONCE(1);
1751 continue;
1752 }
1753
1754 memcpy(bytes, fineibt_paranoid_start, fineibt_paranoid_size);
1755 memcpy(bytes + fineibt_caller_hash, &hash, 4);
1756
1757 if (cpu_wants_indirect_its_thunk_at((unsigned long)addr + fineibt_paranoid_ind, 11)) {
1758 emit_paranoid_trampoline(addr + fineibt_caller_size,
1759 &insn, 11, bytes + fineibt_caller_size);
1760 } else {
1761 int len = fineibt_paranoid_size - fineibt_paranoid_ind;
1762 ret = emit_indirect(op, 11, bytes + fineibt_paranoid_ind, len);
1763 if (WARN_ON_ONCE(ret != len))
1764 continue;
1765 }
1766
1767 text_poke_early(addr, bytes, fineibt_paranoid_size);
1768 }
1769
1770 return 0;
1771 }
1772
1773 #define pr_cfi_debug(X...) if (cfi_debug) pr_info(X)
1774
1775 #define FINEIBT_WARN(_f, _v) \
1776 WARN_ONCE((_f) != (_v), "FineIBT: " #_f " %ld != %d\n", _f, _v)
1777
__apply_fineibt(s32 * start_retpoline,s32 * end_retpoline,s32 * start_cfi,s32 * end_cfi,bool builtin)1778 static void __apply_fineibt(s32 *start_retpoline, s32 *end_retpoline,
1779 s32 *start_cfi, s32 *end_cfi, bool builtin)
1780 {
1781 int ret;
1782
1783 if (FINEIBT_WARN(fineibt_preamble_size, 20) ||
1784 FINEIBT_WARN(fineibt_preamble_bhi + fineibt_bhi1_size, 20) ||
1785 FINEIBT_WARN(fineibt_caller_size, 14) ||
1786 FINEIBT_WARN(fineibt_paranoid_size, 20) ||
1787 WARN_ON_ONCE(CFI_OFFSET < fineibt_prefix_size))
1788 return;
1789
1790 if (cfi_mode == CFI_AUTO) {
1791 cfi_mode = CFI_KCFI;
1792 if (HAS_KERNEL_IBT && cpu_feature_enabled(X86_FEATURE_IBT)) {
1793 /*
1794 * FRED has much saner context on exception entry and
1795 * is less easy to take advantage of.
1796 */
1797 if (!cpu_feature_enabled(X86_FEATURE_FRED))
1798 cfi_paranoid = true;
1799 cfi_mode = CFI_FINEIBT;
1800 }
1801 }
1802
1803 /*
1804 * Rewrite the callers to not use the __cfi_ stubs, such that we might
1805 * rewrite them. This disables all CFI. If this succeeds but any of the
1806 * later stages fails, we're without CFI.
1807 */
1808 pr_cfi_debug("CFI: disabling all indirect call checking\n");
1809 ret = cfi_disable_callers(start_retpoline, end_retpoline);
1810 if (ret)
1811 goto err;
1812
1813 if (cfi_rand) {
1814 if (builtin) {
1815 cfi_seed = get_random_u32();
1816 cfi_bpf_hash = cfi_rehash(cfi_bpf_hash);
1817 cfi_bpf_subprog_hash = cfi_rehash(cfi_bpf_subprog_hash);
1818 }
1819 pr_cfi_debug("CFI: cfi_seed: 0x%08x\n", cfi_seed);
1820
1821 pr_cfi_debug("CFI: rehashing all preambles\n");
1822 ret = cfi_rand_preamble(start_cfi, end_cfi);
1823 if (ret)
1824 goto err;
1825
1826 pr_cfi_debug("CFI: rehashing all indirect calls\n");
1827 ret = cfi_rand_callers(start_retpoline, end_retpoline);
1828 if (ret)
1829 goto err;
1830 } else {
1831 pr_cfi_debug("CFI: rehashing disabled\n");
1832 }
1833
1834 switch (cfi_mode) {
1835 case CFI_OFF:
1836 if (builtin)
1837 pr_info("CFI: disabled\n");
1838 return;
1839
1840 case CFI_KCFI:
1841 pr_cfi_debug("CFI: re-enabling all indirect call checking\n");
1842 ret = cfi_enable_callers(start_retpoline, end_retpoline);
1843 if (ret)
1844 goto err;
1845
1846 if (builtin)
1847 pr_info("CFI: Using %sretpoline kCFI\n",
1848 cfi_rand ? "rehashed " : "");
1849 return;
1850
1851 case CFI_FINEIBT:
1852 pr_cfi_debug("CFI: adding FineIBT to all preambles\n");
1853 /* place the FineIBT preamble at func()-16 */
1854 ret = cfi_rewrite_preamble(start_cfi, end_cfi);
1855 if (ret)
1856 goto err;
1857
1858 /* rewrite the callers to target func()-16 */
1859 pr_cfi_debug("CFI: rewriting indirect call sites to use FineIBT\n");
1860 ret = cfi_rewrite_callers(start_retpoline, end_retpoline);
1861 if (ret)
1862 goto err;
1863
1864 /* now that nobody targets func()+0, remove ENDBR there */
1865 pr_cfi_debug("CFI: removing old endbr insns\n");
1866 cfi_rewrite_endbr(start_cfi, end_cfi);
1867
1868 if (builtin) {
1869 pr_info("Using %sFineIBT%s CFI\n",
1870 cfi_paranoid ? "paranoid " : "",
1871 cfi_bhi ? "+BHI" : "");
1872 }
1873 return;
1874
1875 default:
1876 break;
1877 }
1878
1879 err:
1880 pr_err("Something went horribly wrong trying to rewrite the CFI implementation.\n");
1881 }
1882
poison_hash(void * addr)1883 static inline void poison_hash(void *addr)
1884 {
1885 *(u32 *)addr = 0;
1886 }
1887
poison_cfi(void * addr)1888 static void poison_cfi(void *addr)
1889 {
1890 /*
1891 * Compilers manage to be inconsistent with ENDBR vs __cfi prefixes,
1892 * some (static) functions for which they can determine the address
1893 * is never taken do not get a __cfi prefix, but *DO* get an ENDBR.
1894 *
1895 * As such, these functions will get sealed, but we need to be careful
1896 * to not unconditionally scribble the previous function.
1897 */
1898 switch (cfi_mode) {
1899 case CFI_FINEIBT:
1900 /*
1901 * FineIBT preamble is at func-16.
1902 */
1903 addr += CFI_OFFSET - fineibt_prefix_size;
1904
1905 /*
1906 * FineIBT prefix should start with an ENDBR.
1907 */
1908 if (!is_endbr(addr))
1909 break;
1910
1911 /*
1912 * __cfi_\func:
1913 * nopl -42(%rax)
1914 * sub $0, %eax
1915 * jne \func+3
1916 * \func:
1917 * nopl -42(%rax)
1918 */
1919 poison_endbr(addr);
1920 poison_hash(addr + fineibt_preamble_hash);
1921 break;
1922
1923 case CFI_KCFI:
1924 /*
1925 * kCFI prefix should start with a valid hash.
1926 */
1927 if (!decode_preamble_hash(addr, NULL))
1928 break;
1929
1930 /*
1931 * __cfi_\func:
1932 * movl $0, %eax
1933 * .skip 11, 0x90
1934 */
1935 poison_hash(addr + 1);
1936 break;
1937
1938 default:
1939 break;
1940 }
1941 }
1942
1943 /*
1944 * When regs->ip points to a 0xD6 byte in the FineIBT preamble,
1945 * return true and fill out target and type.
1946 *
1947 * We check the preamble by checking for the ENDBR instruction relative to the
1948 * UDB instruction.
1949 */
decode_fineibt_preamble(struct pt_regs * regs,unsigned long * target,u32 * type)1950 static bool decode_fineibt_preamble(struct pt_regs *regs, unsigned long *target, u32 *type)
1951 {
1952 unsigned long addr = regs->ip - fineibt_preamble_ud;
1953 u32 hash;
1954
1955 if (!exact_endbr((void *)addr))
1956 return false;
1957
1958 *target = addr + fineibt_prefix_size;
1959
1960 __get_kernel_nofault(&hash, addr + fineibt_preamble_hash, u32, Efault);
1961 *type = (u32)regs->ax + hash;
1962
1963 /*
1964 * Since regs->ip points to the middle of an instruction; it cannot
1965 * continue with the normal fixup.
1966 */
1967 regs->ip = *target;
1968
1969 return true;
1970
1971 Efault:
1972 return false;
1973 }
1974
1975 /*
1976 * regs->ip points to one of the UD2 in __bhi_args[].
1977 */
decode_fineibt_bhi(struct pt_regs * regs,unsigned long * target,u32 * type)1978 static bool decode_fineibt_bhi(struct pt_regs *regs, unsigned long *target, u32 *type)
1979 {
1980 unsigned long addr;
1981 u32 hash;
1982
1983 if (!cfi_bhi)
1984 return false;
1985
1986 if (regs->ip < (unsigned long)__bhi_args ||
1987 regs->ip >= (unsigned long)__bhi_args_end)
1988 return false;
1989
1990 /*
1991 * Fetch the return address from the stack, this points to the
1992 * FineIBT preamble. Since the CALL instruction is in the 5 last
1993 * bytes of the preamble, the return address is in fact the target
1994 * address.
1995 */
1996 __get_kernel_nofault(&addr, regs->sp, unsigned long, Efault);
1997 *target = addr;
1998
1999 addr -= fineibt_prefix_size;
2000 if (!exact_endbr((void *)addr))
2001 return false;
2002
2003 __get_kernel_nofault(&hash, addr + fineibt_preamble_hash, u32, Efault);
2004 *type = (u32)regs->ax + hash;
2005
2006 /*
2007 * The UD2 sites are constructed with a RET immediately following,
2008 * as such the non-fatal case can use the regular fixup.
2009 */
2010 return true;
2011
2012 Efault:
2013 return false;
2014 }
2015
is_paranoid_thunk(unsigned long addr)2016 static bool is_paranoid_thunk(unsigned long addr)
2017 {
2018 u32 thunk;
2019
2020 __get_kernel_nofault(&thunk, (u32 *)addr, u32, Efault);
2021 return (thunk & 0x00FFFFFF) == 0xfd75d6;
2022
2023 Efault:
2024 return false;
2025 }
2026
2027 /*
2028 * regs->ip points to a LOCK Jcc.d8 instruction from the fineibt_paranoid_start[]
2029 * sequence, or to UDB + Jcc.d8 for cfi_paranoid + ITS thunk.
2030 */
decode_fineibt_paranoid(struct pt_regs * regs,unsigned long * target,u32 * type)2031 static bool decode_fineibt_paranoid(struct pt_regs *regs, unsigned long *target, u32 *type)
2032 {
2033 unsigned long addr = regs->ip - fineibt_paranoid_ud;
2034
2035 if (!cfi_paranoid)
2036 return false;
2037
2038 if (is_cfi_trap(addr + fineibt_caller_size - LEN_UD2)) {
2039 *target = regs->r11 + fineibt_prefix_size;
2040 *type = regs->ax;
2041
2042 /*
2043 * Since the trapping instruction is the exact, but LOCK prefixed,
2044 * Jcc.d8 that got us here, the normal fixup will work.
2045 */
2046 return true;
2047 }
2048
2049 /*
2050 * The cfi_paranoid + ITS thunk combination results in:
2051 *
2052 * 0: b8 78 56 34 12 mov $0x12345678, %eax
2053 * 5: 41 3b 43 f7 cmp -11(%r11), %eax
2054 * a: 2e 3d 8d 5b f0 cs lea -0x10(%r11), %r11
2055 * e: 2e e8 XX XX XX XX cs call __x86_indirect_paranoid_thunk_r11
2056 *
2057 * Where the paranoid_thunk looks like:
2058 *
2059 * 1d: <d6> udb
2060 * __x86_indirect_paranoid_thunk_r11:
2061 * 1e: 75 fd jne 1d
2062 * __x86_indirect_its_thunk_r11:
2063 * 20: 41 ff eb jmp *%r11
2064 * 23: cc int3
2065 *
2066 */
2067 if (is_paranoid_thunk(regs->ip)) {
2068 *target = regs->r11 + fineibt_prefix_size;
2069 *type = regs->ax;
2070
2071 regs->ip = *target;
2072 return true;
2073 }
2074
2075 return false;
2076 }
2077
decode_fineibt_insn(struct pt_regs * regs,unsigned long * target,u32 * type)2078 bool decode_fineibt_insn(struct pt_regs *regs, unsigned long *target, u32 *type)
2079 {
2080 if (decode_fineibt_paranoid(regs, target, type))
2081 return true;
2082
2083 if (decode_fineibt_bhi(regs, target, type))
2084 return true;
2085
2086 return decode_fineibt_preamble(regs, target, type);
2087 }
2088
2089 #else /* !CONFIG_FINEIBT: */
2090
__apply_fineibt(s32 * start_retpoline,s32 * end_retpoline,s32 * start_cfi,s32 * end_cfi,bool builtin)2091 static void __apply_fineibt(s32 *start_retpoline, s32 *end_retpoline,
2092 s32 *start_cfi, s32 *end_cfi, bool builtin)
2093 {
2094 if (IS_ENABLED(CONFIG_CFI) && builtin)
2095 pr_info("CFI: Using standard kCFI\n");
2096 }
2097
2098 #ifdef CONFIG_X86_KERNEL_IBT
poison_cfi(void * addr)2099 static void poison_cfi(void *addr) { }
2100 #endif
2101
2102 #endif /* !CONFIG_FINEIBT */
2103
apply_fineibt(s32 * start_retpoline,s32 * end_retpoline,s32 * start_cfi,s32 * end_cfi)2104 void apply_fineibt(s32 *start_retpoline, s32 *end_retpoline,
2105 s32 *start_cfi, s32 *end_cfi)
2106 {
2107 return __apply_fineibt(start_retpoline, end_retpoline,
2108 start_cfi, end_cfi,
2109 /* .builtin = */ false);
2110 }
2111
2112 #ifdef CONFIG_SMP
alternatives_smp_lock(const s32 * start,const s32 * end,u8 * text,u8 * text_end)2113 static void alternatives_smp_lock(const s32 *start, const s32 *end,
2114 u8 *text, u8 *text_end)
2115 {
2116 const s32 *poff;
2117
2118 for (poff = start; poff < end; poff++) {
2119 u8 *ptr = (u8 *)poff + *poff;
2120
2121 if (!*poff || ptr < text || ptr >= text_end)
2122 continue;
2123 /* turn DS segment override prefix into lock prefix */
2124 if (*ptr == 0x3e)
2125 text_poke(ptr, ((unsigned char []){0xf0}), 1);
2126 }
2127 }
2128
alternatives_smp_unlock(const s32 * start,const s32 * end,u8 * text,u8 * text_end)2129 static void alternatives_smp_unlock(const s32 *start, const s32 *end,
2130 u8 *text, u8 *text_end)
2131 {
2132 const s32 *poff;
2133
2134 for (poff = start; poff < end; poff++) {
2135 u8 *ptr = (u8 *)poff + *poff;
2136
2137 if (!*poff || ptr < text || ptr >= text_end)
2138 continue;
2139 /* turn lock prefix into DS segment override prefix */
2140 if (*ptr == 0xf0)
2141 text_poke(ptr, ((unsigned char []){0x3E}), 1);
2142 }
2143 }
2144
2145 struct smp_alt_module {
2146 /* what is this ??? */
2147 struct module *mod;
2148 char *name;
2149
2150 /* ptrs to lock prefixes */
2151 const s32 *locks;
2152 const s32 *locks_end;
2153
2154 /* .text segment, needed to avoid patching init code ;) */
2155 u8 *text;
2156 u8 *text_end;
2157
2158 struct list_head next;
2159 };
2160 static LIST_HEAD(smp_alt_modules);
2161 static bool uniproc_patched = false; /* protected by text_mutex */
2162
alternatives_smp_module_add(struct module * mod,char * name,void * locks,void * locks_end,void * text,void * text_end)2163 void __init_or_module alternatives_smp_module_add(struct module *mod,
2164 char *name,
2165 void *locks, void *locks_end,
2166 void *text, void *text_end)
2167 {
2168 struct smp_alt_module *smp;
2169
2170 mutex_lock(&text_mutex);
2171 if (!uniproc_patched)
2172 goto unlock;
2173
2174 if (num_possible_cpus() == 1)
2175 /* Don't bother remembering, we'll never have to undo it. */
2176 goto smp_unlock;
2177
2178 smp = kzalloc_obj(*smp);
2179 if (NULL == smp)
2180 /* we'll run the (safe but slow) SMP code then ... */
2181 goto unlock;
2182
2183 smp->mod = mod;
2184 smp->name = name;
2185 smp->locks = locks;
2186 smp->locks_end = locks_end;
2187 smp->text = text;
2188 smp->text_end = text_end;
2189 DPRINTK(SMP, "locks %p -> %p, text %p -> %p, name %s\n",
2190 smp->locks, smp->locks_end,
2191 smp->text, smp->text_end, smp->name);
2192
2193 list_add_tail(&smp->next, &smp_alt_modules);
2194 smp_unlock:
2195 alternatives_smp_unlock(locks, locks_end, text, text_end);
2196 unlock:
2197 mutex_unlock(&text_mutex);
2198 }
2199
alternatives_smp_module_del(struct module * mod)2200 void __init_or_module alternatives_smp_module_del(struct module *mod)
2201 {
2202 struct smp_alt_module *item;
2203
2204 mutex_lock(&text_mutex);
2205 list_for_each_entry(item, &smp_alt_modules, next) {
2206 if (mod != item->mod)
2207 continue;
2208 list_del(&item->next);
2209 kfree(item);
2210 break;
2211 }
2212 mutex_unlock(&text_mutex);
2213 }
2214
alternatives_enable_smp(void)2215 void alternatives_enable_smp(void)
2216 {
2217 struct smp_alt_module *mod;
2218
2219 /* Why bother if there are no other CPUs? */
2220 BUG_ON(num_possible_cpus() == 1);
2221
2222 mutex_lock(&text_mutex);
2223
2224 if (uniproc_patched) {
2225 pr_info("switching to SMP code\n");
2226 BUG_ON(num_online_cpus() != 1);
2227 clear_cpu_cap(&boot_cpu_data, X86_FEATURE_UP);
2228 clear_cpu_cap(&cpu_data(0), X86_FEATURE_UP);
2229 list_for_each_entry(mod, &smp_alt_modules, next)
2230 alternatives_smp_lock(mod->locks, mod->locks_end,
2231 mod->text, mod->text_end);
2232 uniproc_patched = false;
2233 }
2234 mutex_unlock(&text_mutex);
2235 }
2236
2237 /*
2238 * Return 1 if the address range is reserved for SMP-alternatives.
2239 * Must hold text_mutex.
2240 */
alternatives_text_reserved(void * start,void * end)2241 int alternatives_text_reserved(void *start, void *end)
2242 {
2243 struct smp_alt_module *mod;
2244 const s32 *poff;
2245 u8 *text_start = start;
2246 u8 *text_end = end;
2247
2248 lockdep_assert_held(&text_mutex);
2249
2250 list_for_each_entry(mod, &smp_alt_modules, next) {
2251 if (mod->text > text_end || mod->text_end < text_start)
2252 continue;
2253 for (poff = mod->locks; poff < mod->locks_end; poff++) {
2254 const u8 *ptr = (const u8 *)poff + *poff;
2255
2256 if (text_start <= ptr && text_end > ptr)
2257 return 1;
2258 }
2259 }
2260
2261 return 0;
2262 }
2263 #endif /* CONFIG_SMP */
2264
2265 /*
2266 * Self-test for the INT3 based CALL emulation code.
2267 *
2268 * This exercises int3_emulate_call() to make sure INT3 pt_regs are set up
2269 * properly and that there is a stack gap between the INT3 frame and the
2270 * previous context. Without this gap doing a virtual PUSH on the interrupted
2271 * stack would corrupt the INT3 IRET frame.
2272 *
2273 * See entry_{32,64}.S for more details.
2274 */
2275
2276 extern void int3_selftest_asm(unsigned int *ptr);
2277
2278 asm (
2279 " .pushsection .init.text, \"ax\", @progbits\n"
2280 " .type int3_selftest_asm, @function\n"
2281 "int3_selftest_asm:\n"
2282 ANNOTATE_NOENDBR "\n"
2283 /*
2284 * INT3 padded with NOP to CALL_INSN_SIZE. The INT3 triggers an
2285 * exception, then the int3_exception_nb notifier emulates a call to
2286 * int3_selftest_callee().
2287 */
2288 " int3; nop; nop; nop; nop\n"
2289 ASM_RET
2290 " .size int3_selftest_asm, . - int3_selftest_asm\n"
2291 " .popsection\n"
2292 );
2293
2294 extern void int3_selftest_callee(unsigned int *ptr);
2295
2296 asm (
2297 " .pushsection .init.text, \"ax\", @progbits\n"
2298 " .type int3_selftest_callee, @function\n"
2299 "int3_selftest_callee:\n"
2300 ANNOTATE_NOENDBR "\n"
2301 " movl $0x1234, (%" _ASM_ARG1 ")\n"
2302 ASM_RET
2303 " .size int3_selftest_callee, . - int3_selftest_callee\n"
2304 " .popsection\n"
2305 );
2306
2307 extern void int3_selftest_ip(void); /* defined in asm below */
2308
2309 static int __init
int3_exception_notify(struct notifier_block * self,unsigned long val,void * data)2310 int3_exception_notify(struct notifier_block *self, unsigned long val, void *data)
2311 {
2312 unsigned long selftest = (unsigned long)&int3_selftest_asm;
2313 struct die_args *args = data;
2314 struct pt_regs *regs = args->regs;
2315
2316 OPTIMIZER_HIDE_VAR(selftest);
2317
2318 if (!regs || user_mode(regs))
2319 return NOTIFY_DONE;
2320
2321 if (val != DIE_INT3)
2322 return NOTIFY_DONE;
2323
2324 if (regs->ip - INT3_INSN_SIZE != selftest)
2325 return NOTIFY_DONE;
2326
2327 int3_emulate_call(regs, (unsigned long)&int3_selftest_callee);
2328 return NOTIFY_STOP;
2329 }
2330
2331 /* Must be noinline to ensure uniqueness of int3_selftest_ip. */
int3_selftest(void)2332 static noinline void __init int3_selftest(void)
2333 {
2334 static __initdata struct notifier_block int3_exception_nb = {
2335 .notifier_call = int3_exception_notify,
2336 .priority = INT_MAX-1, /* last */
2337 };
2338 unsigned int val = 0;
2339
2340 BUG_ON(register_die_notifier(&int3_exception_nb));
2341
2342 /*
2343 * Basically: int3_selftest_callee(&val); but really complicated :-)
2344 */
2345 int3_selftest_asm(&val);
2346
2347 BUG_ON(val != 0x1234);
2348
2349 unregister_die_notifier(&int3_exception_nb);
2350 }
2351
2352 static __initdata int __alt_reloc_selftest_addr;
2353
2354 extern void __init __alt_reloc_selftest(void *arg);
__alt_reloc_selftest(void * arg)2355 __visible noinline void __init __alt_reloc_selftest(void *arg)
2356 {
2357 WARN_ON(arg != &__alt_reloc_selftest_addr);
2358 }
2359
alt_reloc_selftest(void)2360 static noinline void __init alt_reloc_selftest(void)
2361 {
2362 /*
2363 * Tests text_poke_apply_relocation().
2364 *
2365 * This has a relative immediate (CALL) in a place other than the first
2366 * instruction and additionally on x86_64 we get a RIP-relative LEA:
2367 *
2368 * lea 0x0(%rip),%rdi # 5d0: R_X86_64_PC32 .init.data+0x5566c
2369 * call +0 # 5d5: R_X86_64_PLT32 __alt_reloc_selftest-0x4
2370 *
2371 * Getting this wrong will either crash and burn or tickle the WARN
2372 * above.
2373 */
2374 asm_inline volatile (
2375 ALTERNATIVE("", "lea %[mem], %%" _ASM_ARG1 "; call __alt_reloc_selftest;", X86_FEATURE_ALWAYS)
2376 : ASM_CALL_CONSTRAINT
2377 : [mem] "m" (__alt_reloc_selftest_addr)
2378 : _ASM_ARG1
2379 );
2380 }
2381
alternative_instructions(void)2382 void __init alternative_instructions(void)
2383 {
2384 u64 ibt;
2385
2386 int3_selftest();
2387
2388 /*
2389 * The patching is not fully atomic, so try to avoid local
2390 * interruptions that might execute the to be patched code.
2391 * Other CPUs are not running.
2392 */
2393 stop_nmi();
2394
2395 /*
2396 * Don't stop machine check exceptions while patching.
2397 * MCEs only happen when something got corrupted and in this
2398 * case we must do something about the corruption.
2399 * Ignoring it is worse than an unlikely patching race.
2400 * Also machine checks tend to be broadcast and if one CPU
2401 * goes into machine check the others follow quickly, so we don't
2402 * expect a machine check to cause undue problems during to code
2403 * patching.
2404 */
2405
2406 /*
2407 * Make sure to set (artificial) features depending on used paravirt
2408 * functions which can later influence alternative patching.
2409 */
2410 paravirt_set_cap();
2411
2412 /* Keep CET-IBT disabled until caller/callee are patched */
2413 ibt = ibt_save(/*disable*/ true);
2414
2415 __apply_fineibt(__retpoline_sites, __retpoline_sites_end,
2416 __cfi_sites, __cfi_sites_end, true);
2417 cfi_debug = false;
2418
2419 /*
2420 * Rewrite the retpolines, must be done before alternatives since
2421 * those can rewrite the retpoline thunks.
2422 */
2423 apply_retpolines(__retpoline_sites, __retpoline_sites_end);
2424 apply_returns(__return_sites, __return_sites_end);
2425
2426 its_fini_core();
2427
2428 /*
2429 * Adjust all CALL instructions to point to func()-10, including
2430 * those in .altinstr_replacement.
2431 */
2432 callthunks_patch_builtin_calls();
2433
2434 apply_alternatives(__alt_instructions, __alt_instructions_end);
2435
2436 /*
2437 * Seal all functions that do not have their address taken.
2438 */
2439 apply_seal_endbr(__ibt_endbr_seal, __ibt_endbr_seal_end);
2440
2441 ibt_restore(ibt);
2442
2443 #ifdef CONFIG_SMP
2444 /* Patch to UP if other cpus not imminent. */
2445 if (!noreplace_smp && (num_present_cpus() == 1 || setup_max_cpus <= 1)) {
2446 uniproc_patched = true;
2447 alternatives_smp_module_add(NULL, "core kernel",
2448 __smp_locks, __smp_locks_end,
2449 _text, _etext);
2450 }
2451
2452 if (!uniproc_patched || num_possible_cpus() == 1) {
2453 free_init_pages("SMP alternatives",
2454 (unsigned long)__smp_locks,
2455 (unsigned long)__smp_locks_end);
2456 }
2457 #endif
2458
2459 restart_nmi();
2460 alternatives_patched = 1;
2461
2462 alt_reloc_selftest();
2463 }
2464
2465 /**
2466 * text_poke_early - Update instructions on a live kernel at boot time
2467 * @addr: address to modify
2468 * @opcode: source of the copy
2469 * @len: length to copy
2470 *
2471 * When you use this code to patch more than one byte of an instruction
2472 * you need to make sure that other CPUs cannot execute this code in parallel.
2473 * Also no thread must be currently preempted in the middle of these
2474 * instructions. And on the local CPU you need to be protected against NMI or
2475 * MCE handlers seeing an inconsistent instruction while you patch.
2476 */
text_poke_early(void * addr,const void * opcode,size_t len)2477 void __init_or_module text_poke_early(void *addr, const void *opcode,
2478 size_t len)
2479 {
2480 unsigned long flags;
2481
2482 if (boot_cpu_has(X86_FEATURE_NX) &&
2483 is_module_text_address((unsigned long)addr)) {
2484 /*
2485 * Modules text is marked initially as non-executable, so the
2486 * code cannot be running and speculative code-fetches are
2487 * prevented. Just change the code.
2488 */
2489 memcpy(addr, opcode, len);
2490 } else {
2491 local_irq_save(flags);
2492 memcpy(addr, opcode, len);
2493 sync_core();
2494 local_irq_restore(flags);
2495
2496 /*
2497 * Could also do a CLFLUSH here to speed up CPU recovery; but
2498 * that causes hangs on some VIA CPUs.
2499 */
2500 }
2501 }
2502
2503 __ro_after_init struct mm_struct *text_poke_mm;
2504 __ro_after_init unsigned long text_poke_mm_addr;
2505
2506 /*
2507 * Text poking creates and uses a mapping in the lower half of the
2508 * address space. Relax LASS enforcement when accessing the poking
2509 * address.
2510 *
2511 * objtool enforces a strict policy of "no function calls within AC=1
2512 * regions". Adhere to the policy by using inline versions of
2513 * memcpy()/memset() that will never result in a function call.
2514 */
2515
text_poke_memcpy(void * dst,const void * src,size_t len)2516 static void text_poke_memcpy(void *dst, const void *src, size_t len)
2517 {
2518 lass_stac();
2519 __inline_memcpy(dst, src, len);
2520 lass_clac();
2521 }
2522
text_poke_memset(void * dst,const void * src,size_t len)2523 static void text_poke_memset(void *dst, const void *src, size_t len)
2524 {
2525 int c = *(const int *)src;
2526
2527 lass_stac();
2528 __inline_memset(dst, c, len);
2529 lass_clac();
2530 }
2531
2532 typedef void text_poke_f(void *dst, const void *src, size_t len);
2533
__text_poke(text_poke_f func,void * addr,const void * src,size_t len)2534 static void *__text_poke(text_poke_f func, void *addr, const void *src, size_t len)
2535 {
2536 bool cross_page_boundary = offset_in_page(addr) + len > PAGE_SIZE;
2537 struct page *pages[2] = {NULL};
2538 struct mm_struct *prev_mm;
2539 unsigned long flags;
2540 pte_t pte, *ptep;
2541 spinlock_t *ptl;
2542 pgprot_t pgprot;
2543
2544 /*
2545 * While boot memory allocator is running we cannot use struct pages as
2546 * they are not yet initialized. There is no way to recover.
2547 */
2548 BUG_ON(!after_bootmem);
2549
2550 if (!core_kernel_text((unsigned long)addr)) {
2551 pages[0] = vmalloc_to_page(addr);
2552 if (cross_page_boundary)
2553 pages[1] = vmalloc_to_page(addr + PAGE_SIZE);
2554 } else {
2555 pages[0] = virt_to_page(addr);
2556 WARN_ON(!PageReserved(pages[0]));
2557 if (cross_page_boundary)
2558 pages[1] = virt_to_page(addr + PAGE_SIZE);
2559 }
2560 /*
2561 * If something went wrong, crash and burn since recovery paths are not
2562 * implemented.
2563 */
2564 BUG_ON(!pages[0] || (cross_page_boundary && !pages[1]));
2565
2566 /*
2567 * Map the page without the global bit, as TLB flushing is done with
2568 * flush_tlb_mm_range(), which is intended for non-global PTEs.
2569 */
2570 pgprot = __pgprot(pgprot_val(PAGE_KERNEL) & ~_PAGE_GLOBAL);
2571
2572 /*
2573 * The lock is not really needed, but this allows to avoid open-coding.
2574 */
2575 ptep = get_locked_pte(text_poke_mm, text_poke_mm_addr, &ptl);
2576
2577 /*
2578 * This must not fail; preallocated in poking_init().
2579 */
2580 VM_BUG_ON(!ptep);
2581
2582 local_irq_save(flags);
2583
2584 pte = mk_pte(pages[0], pgprot);
2585 set_pte_at(text_poke_mm, text_poke_mm_addr, ptep, pte);
2586
2587 if (cross_page_boundary) {
2588 pte = mk_pte(pages[1], pgprot);
2589 set_pte_at(text_poke_mm, text_poke_mm_addr + PAGE_SIZE, ptep + 1, pte);
2590 }
2591
2592 /*
2593 * Loading the temporary mm behaves as a compiler barrier, which
2594 * guarantees that the PTE will be set at the time memcpy() is done.
2595 */
2596 prev_mm = use_temporary_mm(text_poke_mm);
2597
2598 kasan_disable_current();
2599 func((u8 *)text_poke_mm_addr + offset_in_page(addr), src, len);
2600 kasan_enable_current();
2601
2602 /*
2603 * Ensure that the PTE is only cleared after the instructions of memcpy
2604 * were issued by using a compiler barrier.
2605 */
2606 barrier();
2607
2608 pte_clear(text_poke_mm, text_poke_mm_addr, ptep);
2609 if (cross_page_boundary)
2610 pte_clear(text_poke_mm, text_poke_mm_addr + PAGE_SIZE, ptep + 1);
2611
2612 /*
2613 * Loading the previous page-table hierarchy requires a serializing
2614 * instruction that already allows the core to see the updated version.
2615 * Xen-PV is assumed to serialize execution in a similar manner.
2616 */
2617 unuse_temporary_mm(prev_mm);
2618
2619 /*
2620 * Flushing the TLB might involve IPIs, which would require enabled
2621 * IRQs, but not if the mm is not used, as it is in this point.
2622 */
2623 flush_tlb_mm_range(text_poke_mm, text_poke_mm_addr, text_poke_mm_addr +
2624 (cross_page_boundary ? 2 : 1) * PAGE_SIZE,
2625 PAGE_SHIFT, false);
2626
2627 if (func == text_poke_memcpy) {
2628 /*
2629 * If the text does not match what we just wrote then something is
2630 * fundamentally screwy; there's nothing we can really do about that.
2631 */
2632 BUG_ON(memcmp(addr, src, len));
2633 }
2634
2635 local_irq_restore(flags);
2636 pte_unmap_unlock(ptep, ptl);
2637 return addr;
2638 }
2639
2640 /**
2641 * text_poke - Update instructions on a live kernel
2642 * @addr: address to modify
2643 * @opcode: source of the copy
2644 * @len: length to copy
2645 *
2646 * Only atomic text poke/set should be allowed when not doing early patching.
2647 * It means the size must be writable atomically and the address must be aligned
2648 * in a way that permits an atomic write. It also makes sure we fit on a single
2649 * page.
2650 *
2651 * Note that the caller must ensure that if the modified code is part of a
2652 * module, the module would not be removed during poking. This can be achieved
2653 * by registering a module notifier, and ordering module removal and patching
2654 * through a mutex.
2655 */
text_poke(void * addr,const void * opcode,size_t len)2656 void *text_poke(void *addr, const void *opcode, size_t len)
2657 {
2658 lockdep_assert_held(&text_mutex);
2659
2660 return __text_poke(text_poke_memcpy, addr, opcode, len);
2661 }
2662
2663 /**
2664 * text_poke_kgdb - Update instructions on a live kernel by kgdb
2665 * @addr: address to modify
2666 * @opcode: source of the copy
2667 * @len: length to copy
2668 *
2669 * Only atomic text poke/set should be allowed when not doing early patching.
2670 * It means the size must be writable atomically and the address must be aligned
2671 * in a way that permits an atomic write. It also makes sure we fit on a single
2672 * page.
2673 *
2674 * Context: should only be used by kgdb, which ensures no other core is running,
2675 * despite the fact it does not hold the text_mutex.
2676 */
text_poke_kgdb(void * addr,const void * opcode,size_t len)2677 void *text_poke_kgdb(void *addr, const void *opcode, size_t len)
2678 {
2679 return __text_poke(text_poke_memcpy, addr, opcode, len);
2680 }
2681
text_poke_copy_locked(void * addr,const void * opcode,size_t len,bool core_ok)2682 void *text_poke_copy_locked(void *addr, const void *opcode, size_t len,
2683 bool core_ok)
2684 {
2685 unsigned long start = (unsigned long)addr;
2686 size_t patched = 0;
2687
2688 if (WARN_ON_ONCE(!core_ok && core_kernel_text(start)))
2689 return NULL;
2690
2691 while (patched < len) {
2692 unsigned long ptr = start + patched;
2693 size_t s;
2694
2695 s = min_t(size_t, PAGE_SIZE * 2 - offset_in_page(ptr), len - patched);
2696
2697 __text_poke(text_poke_memcpy, (void *)ptr, opcode + patched, s);
2698 patched += s;
2699 }
2700 return addr;
2701 }
2702
2703 /**
2704 * text_poke_copy - Copy instructions into (an unused part of) RX memory
2705 * @addr: address to modify
2706 * @opcode: source of the copy
2707 * @len: length to copy, could be more than 2x PAGE_SIZE
2708 *
2709 * Not safe against concurrent execution; useful for JITs to dump
2710 * new code blocks into unused regions of RX memory. Can be used in
2711 * conjunction with synchronize_rcu_tasks() to wait for existing
2712 * execution to quiesce after having made sure no existing functions
2713 * pointers are live.
2714 */
text_poke_copy(void * addr,const void * opcode,size_t len)2715 void *text_poke_copy(void *addr, const void *opcode, size_t len)
2716 {
2717 mutex_lock(&text_mutex);
2718 addr = text_poke_copy_locked(addr, opcode, len, false);
2719 mutex_unlock(&text_mutex);
2720 return addr;
2721 }
2722
2723 /**
2724 * text_poke_set - memset into (an unused part of) RX memory
2725 * @addr: address to modify
2726 * @c: the byte to fill the area with
2727 * @len: length to copy, could be more than 2x PAGE_SIZE
2728 *
2729 * This is useful to overwrite unused regions of RX memory with illegal
2730 * instructions.
2731 */
text_poke_set(void * addr,int c,size_t len)2732 void *text_poke_set(void *addr, int c, size_t len)
2733 {
2734 unsigned long start = (unsigned long)addr;
2735 size_t patched = 0;
2736
2737 if (WARN_ON_ONCE(core_kernel_text(start)))
2738 return NULL;
2739
2740 mutex_lock(&text_mutex);
2741 while (patched < len) {
2742 unsigned long ptr = start + patched;
2743 size_t s;
2744
2745 s = min_t(size_t, PAGE_SIZE * 2 - offset_in_page(ptr), len - patched);
2746
2747 __text_poke(text_poke_memset, (void *)ptr, (void *)&c, s);
2748 patched += s;
2749 }
2750 mutex_unlock(&text_mutex);
2751 return addr;
2752 }
2753
do_sync_core(void * info)2754 static void do_sync_core(void *info)
2755 {
2756 sync_core();
2757 }
2758
smp_text_poke_sync_each_cpu(void)2759 void smp_text_poke_sync_each_cpu(void)
2760 {
2761 on_each_cpu(do_sync_core, NULL, 1);
2762 }
2763
2764 /*
2765 * NOTE: crazy scheme to allow patching Jcc.d32 but not increase the size of
2766 * this thing. When len == 6 everything is prefixed with 0x0f and we map
2767 * opcode to Jcc.d8, using len to distinguish.
2768 */
2769 struct smp_text_poke_loc {
2770 /* addr := _stext + rel_addr */
2771 s32 rel_addr;
2772 s32 disp;
2773 u8 len;
2774 u8 opcode;
2775 const u8 text[TEXT_POKE_MAX_OPCODE_SIZE];
2776 /* see smp_text_poke_batch_finish() */
2777 u8 old;
2778 };
2779
2780 #define TEXT_POKE_ARRAY_MAX (PAGE_SIZE / sizeof(struct smp_text_poke_loc))
2781
2782 static struct smp_text_poke_array {
2783 struct smp_text_poke_loc vec[TEXT_POKE_ARRAY_MAX];
2784 int nr_entries;
2785 } text_poke_array;
2786
2787 static DEFINE_PER_CPU(atomic_t, text_poke_array_refs);
2788
2789 /*
2790 * These four __always_inline annotations imply noinstr, necessary
2791 * due to smp_text_poke_int3_handler() being noinstr:
2792 */
2793
try_get_text_poke_array(void)2794 static __always_inline bool try_get_text_poke_array(void)
2795 {
2796 atomic_t *refs = this_cpu_ptr(&text_poke_array_refs);
2797
2798 if (!raw_atomic_inc_not_zero(refs))
2799 return false;
2800
2801 return true;
2802 }
2803
put_text_poke_array(void)2804 static __always_inline void put_text_poke_array(void)
2805 {
2806 atomic_t *refs = this_cpu_ptr(&text_poke_array_refs);
2807
2808 smp_mb__before_atomic();
2809 raw_atomic_dec(refs);
2810 }
2811
text_poke_addr(const struct smp_text_poke_loc * tpl)2812 static __always_inline void *text_poke_addr(const struct smp_text_poke_loc *tpl)
2813 {
2814 return _stext + tpl->rel_addr;
2815 }
2816
patch_cmp(const void * tpl_a,const void * tpl_b)2817 static __always_inline int patch_cmp(const void *tpl_a, const void *tpl_b)
2818 {
2819 if (tpl_a < text_poke_addr(tpl_b))
2820 return -1;
2821 if (tpl_a > text_poke_addr(tpl_b))
2822 return 1;
2823 return 0;
2824 }
2825
smp_text_poke_int3_handler(struct pt_regs * regs)2826 noinstr int smp_text_poke_int3_handler(struct pt_regs *regs)
2827 {
2828 struct smp_text_poke_loc *tpl;
2829 int ret = 0;
2830 void *ip;
2831
2832 if (user_mode(regs))
2833 return 0;
2834
2835 /*
2836 * Having observed our INT3 instruction, we now must observe
2837 * text_poke_array with non-zero refcount:
2838 *
2839 * text_poke_array_refs = 1 INT3
2840 * WMB RMB
2841 * write INT3 if (text_poke_array_refs != 0)
2842 */
2843 smp_rmb();
2844
2845 if (!try_get_text_poke_array())
2846 return 0;
2847
2848 /*
2849 * Discount the INT3. See smp_text_poke_batch_finish().
2850 */
2851 ip = (void *) regs->ip - INT3_INSN_SIZE;
2852
2853 /*
2854 * Skip the binary search if there is a single member in the vector.
2855 */
2856 if (unlikely(text_poke_array.nr_entries > 1)) {
2857 tpl = __inline_bsearch(ip, text_poke_array.vec, text_poke_array.nr_entries,
2858 sizeof(struct smp_text_poke_loc),
2859 patch_cmp);
2860 if (!tpl)
2861 goto out_put;
2862 } else {
2863 tpl = text_poke_array.vec;
2864 if (text_poke_addr(tpl) != ip)
2865 goto out_put;
2866 }
2867
2868 ip += tpl->len;
2869
2870 switch (tpl->opcode) {
2871 case INT3_INSN_OPCODE:
2872 /*
2873 * Someone poked an explicit INT3, they'll want to handle it,
2874 * do not consume.
2875 */
2876 goto out_put;
2877
2878 case RET_INSN_OPCODE:
2879 int3_emulate_ret(regs);
2880 break;
2881
2882 case CALL_INSN_OPCODE:
2883 int3_emulate_call(regs, (long)ip + tpl->disp);
2884 break;
2885
2886 case JMP32_INSN_OPCODE:
2887 case JMP8_INSN_OPCODE:
2888 int3_emulate_jmp(regs, (long)ip + tpl->disp);
2889 break;
2890
2891 case 0x70 ... 0x7f: /* Jcc */
2892 int3_emulate_jcc(regs, tpl->opcode & 0xf, (long)ip, tpl->disp);
2893 break;
2894
2895 default:
2896 BUG();
2897 }
2898
2899 ret = 1;
2900
2901 out_put:
2902 put_text_poke_array();
2903 return ret;
2904 }
2905
2906 /**
2907 * smp_text_poke_batch_finish() -- update instructions on live kernel on SMP
2908 *
2909 * Input state:
2910 * text_poke_array.vec: vector of instructions to patch
2911 * text_poke_array.nr_entries: number of entries in the vector
2912 *
2913 * Modify multi-byte instructions by using INT3 breakpoints on SMP.
2914 * We completely avoid using stop_machine() here, and achieve the
2915 * synchronization using INT3 breakpoints and SMP cross-calls.
2916 *
2917 * The way it is done:
2918 * - For each entry in the vector:
2919 * - add an INT3 trap to the address that will be patched
2920 * - SMP sync all CPUs
2921 * - For each entry in the vector:
2922 * - update all but the first byte of the patched range
2923 * - SMP sync all CPUs
2924 * - For each entry in the vector:
2925 * - replace the first byte (INT3) by the first byte of the
2926 * replacing opcode
2927 * - SMP sync all CPUs
2928 */
smp_text_poke_batch_finish(void)2929 void smp_text_poke_batch_finish(void)
2930 {
2931 unsigned char int3 = INT3_INSN_OPCODE;
2932 unsigned int i;
2933 int do_sync;
2934
2935 if (!text_poke_array.nr_entries)
2936 return;
2937
2938 lockdep_assert_held(&text_mutex);
2939
2940 /*
2941 * Corresponds to the implicit memory barrier in try_get_text_poke_array() to
2942 * ensure reading a non-zero refcount provides up to date text_poke_array data.
2943 */
2944 for_each_possible_cpu(i)
2945 atomic_set_release(per_cpu_ptr(&text_poke_array_refs, i), 1);
2946
2947 /*
2948 * Function tracing can enable thousands of places that need to be
2949 * updated. This can take quite some time, and with full kernel debugging
2950 * enabled, this could cause the softlockup watchdog to trigger.
2951 * This function gets called every 256 entries added to be patched.
2952 * Call cond_resched() here to make sure that other tasks can get scheduled
2953 * while processing all the functions being patched.
2954 */
2955 cond_resched();
2956
2957 /*
2958 * Corresponding read barrier in INT3 notifier for making sure the
2959 * text_poke_array.nr_entries and handler are correctly ordered wrt. patching.
2960 */
2961 smp_wmb();
2962
2963 /*
2964 * First step: add a INT3 trap to the address that will be patched.
2965 */
2966 for (i = 0; i < text_poke_array.nr_entries; i++) {
2967 text_poke_array.vec[i].old = *(u8 *)text_poke_addr(&text_poke_array.vec[i]);
2968 text_poke(text_poke_addr(&text_poke_array.vec[i]), &int3, INT3_INSN_SIZE);
2969 }
2970
2971 smp_text_poke_sync_each_cpu();
2972
2973 /*
2974 * Second step: update all but the first byte of the patched range.
2975 */
2976 for (do_sync = 0, i = 0; i < text_poke_array.nr_entries; i++) {
2977 u8 old[TEXT_POKE_MAX_OPCODE_SIZE+1] = { text_poke_array.vec[i].old, };
2978 u8 _new[TEXT_POKE_MAX_OPCODE_SIZE+1];
2979 const u8 *new = text_poke_array.vec[i].text;
2980 int len = text_poke_array.vec[i].len;
2981
2982 if (len - INT3_INSN_SIZE > 0) {
2983 memcpy(old + INT3_INSN_SIZE,
2984 text_poke_addr(&text_poke_array.vec[i]) + INT3_INSN_SIZE,
2985 len - INT3_INSN_SIZE);
2986
2987 if (len == 6) {
2988 _new[0] = 0x0f;
2989 memcpy(_new + 1, new, 5);
2990 new = _new;
2991 }
2992
2993 text_poke(text_poke_addr(&text_poke_array.vec[i]) + INT3_INSN_SIZE,
2994 new + INT3_INSN_SIZE,
2995 len - INT3_INSN_SIZE);
2996
2997 do_sync++;
2998 }
2999
3000 /*
3001 * Emit a perf event to record the text poke, primarily to
3002 * support Intel PT decoding which must walk the executable code
3003 * to reconstruct the trace. The flow up to here is:
3004 * - write INT3 byte
3005 * - IPI-SYNC
3006 * - write instruction tail
3007 * At this point the actual control flow will be through the
3008 * INT3 and handler and not hit the old or new instruction.
3009 * Intel PT outputs FUP/TIP packets for the INT3, so the flow
3010 * can still be decoded. Subsequently:
3011 * - emit RECORD_TEXT_POKE with the new instruction
3012 * - IPI-SYNC
3013 * - write first byte
3014 * - IPI-SYNC
3015 * So before the text poke event timestamp, the decoder will see
3016 * either the old instruction flow or FUP/TIP of INT3. After the
3017 * text poke event timestamp, the decoder will see either the
3018 * new instruction flow or FUP/TIP of INT3. Thus decoders can
3019 * use the timestamp as the point at which to modify the
3020 * executable code.
3021 * The old instruction is recorded so that the event can be
3022 * processed forwards or backwards.
3023 */
3024 perf_event_text_poke(text_poke_addr(&text_poke_array.vec[i]), old, len, new, len);
3025 }
3026
3027 if (do_sync) {
3028 /*
3029 * According to Intel, this core syncing is very likely
3030 * not necessary and we'd be safe even without it. But
3031 * better safe than sorry (plus there's not only Intel).
3032 */
3033 smp_text_poke_sync_each_cpu();
3034 }
3035
3036 /*
3037 * Third step: replace the first byte (INT3) by the first byte of the
3038 * replacing opcode.
3039 */
3040 for (do_sync = 0, i = 0; i < text_poke_array.nr_entries; i++) {
3041 u8 byte = text_poke_array.vec[i].text[0];
3042
3043 if (text_poke_array.vec[i].len == 6)
3044 byte = 0x0f;
3045
3046 if (byte == INT3_INSN_OPCODE)
3047 continue;
3048
3049 text_poke(text_poke_addr(&text_poke_array.vec[i]), &byte, INT3_INSN_SIZE);
3050 do_sync++;
3051 }
3052
3053 if (do_sync)
3054 smp_text_poke_sync_each_cpu();
3055
3056 /*
3057 * Remove and wait for refs to be zero.
3058 *
3059 * Notably, if after step-3 above the INT3 got removed, then the
3060 * smp_text_poke_sync_each_cpu() will have serialized against any running INT3
3061 * handlers and the below spin-wait will not happen.
3062 *
3063 * IOW. unless the replacement instruction is INT3, this case goes
3064 * unused.
3065 */
3066 for_each_possible_cpu(i) {
3067 atomic_t *refs = per_cpu_ptr(&text_poke_array_refs, i);
3068
3069 if (unlikely(!atomic_dec_and_test(refs)))
3070 atomic_cond_read_acquire(refs, !VAL);
3071 }
3072
3073 /* They are all completed: */
3074 text_poke_array.nr_entries = 0;
3075 }
3076
__smp_text_poke_batch_add(void * addr,const void * opcode,size_t len,const void * emulate)3077 static void __smp_text_poke_batch_add(void *addr, const void *opcode, size_t len, const void *emulate)
3078 {
3079 struct smp_text_poke_loc *tpl;
3080 struct insn insn;
3081 int ret, i = 0;
3082
3083 tpl = &text_poke_array.vec[text_poke_array.nr_entries++];
3084
3085 if (len == 6)
3086 i = 1;
3087 memcpy((void *)tpl->text, opcode+i, len-i);
3088 if (!emulate)
3089 emulate = opcode;
3090
3091 ret = insn_decode_kernel(&insn, emulate);
3092 BUG_ON(ret < 0);
3093
3094 tpl->rel_addr = addr - (void *)_stext;
3095 tpl->len = len;
3096 tpl->opcode = insn.opcode.bytes[0];
3097
3098 if (is_jcc32(&insn)) {
3099 /*
3100 * Map Jcc.d32 onto Jcc.d8 and use len to distinguish.
3101 */
3102 tpl->opcode = insn.opcode.bytes[1] - 0x10;
3103 }
3104
3105 switch (tpl->opcode) {
3106 case RET_INSN_OPCODE:
3107 case JMP32_INSN_OPCODE:
3108 case JMP8_INSN_OPCODE:
3109 /*
3110 * Control flow instructions without implied execution of the
3111 * next instruction can be padded with INT3.
3112 */
3113 for (i = insn.length; i < len; i++)
3114 BUG_ON(tpl->text[i] != INT3_INSN_OPCODE);
3115 break;
3116
3117 default:
3118 BUG_ON(len != insn.length);
3119 }
3120
3121 switch (tpl->opcode) {
3122 case INT3_INSN_OPCODE:
3123 case RET_INSN_OPCODE:
3124 break;
3125
3126 case CALL_INSN_OPCODE:
3127 case JMP32_INSN_OPCODE:
3128 case JMP8_INSN_OPCODE:
3129 case 0x70 ... 0x7f: /* Jcc */
3130 tpl->disp = insn.immediate.value;
3131 break;
3132
3133 default: /* assume NOP */
3134 switch (len) {
3135 case 2: /* NOP2 -- emulate as JMP8+0 */
3136 BUG_ON(memcmp(emulate, x86_nops[len], len));
3137 tpl->opcode = JMP8_INSN_OPCODE;
3138 tpl->disp = 0;
3139 break;
3140
3141 case 5: /* NOP5 -- emulate as JMP32+0 */
3142 BUG_ON(memcmp(emulate, x86_nops[len], len));
3143 tpl->opcode = JMP32_INSN_OPCODE;
3144 tpl->disp = 0;
3145 break;
3146
3147 default: /* unknown instruction */
3148 BUG();
3149 }
3150 break;
3151 }
3152 }
3153
3154 /*
3155 * We hard rely on the text_poke_array.vec being ordered; ensure this is so by flushing
3156 * early if needed.
3157 */
text_poke_addr_ordered(void * addr)3158 static bool text_poke_addr_ordered(void *addr)
3159 {
3160 WARN_ON_ONCE(!addr);
3161
3162 if (!text_poke_array.nr_entries)
3163 return true;
3164
3165 /*
3166 * If the last current entry's address is higher than the
3167 * new entry's address we'd like to add, then ordering
3168 * is violated and we must first flush all pending patching
3169 * requests:
3170 */
3171 if (text_poke_addr(text_poke_array.vec + text_poke_array.nr_entries-1) > addr)
3172 return false;
3173
3174 return true;
3175 }
3176
3177 /**
3178 * smp_text_poke_batch_add() -- update instruction on live kernel on SMP, batched
3179 * @addr: address to patch
3180 * @opcode: opcode of new instruction
3181 * @len: length to copy
3182 * @emulate: instruction to be emulated
3183 *
3184 * Add a new instruction to the current queue of to-be-patched instructions
3185 * the kernel maintains. The patching request will not be executed immediately,
3186 * but becomes part of an array of patching requests, optimized for batched
3187 * execution. All pending patching requests will be executed on the next
3188 * smp_text_poke_batch_finish() call.
3189 */
smp_text_poke_batch_add(void * addr,const void * opcode,size_t len,const void * emulate)3190 void __ref smp_text_poke_batch_add(void *addr, const void *opcode, size_t len, const void *emulate)
3191 {
3192 if (text_poke_array.nr_entries == TEXT_POKE_ARRAY_MAX || !text_poke_addr_ordered(addr))
3193 smp_text_poke_batch_finish();
3194 __smp_text_poke_batch_add(addr, opcode, len, emulate);
3195 }
3196
3197 /**
3198 * smp_text_poke_single() -- update instruction on live kernel on SMP immediately
3199 * @addr: address to patch
3200 * @opcode: opcode of new instruction
3201 * @len: length to copy
3202 * @emulate: instruction to be emulated
3203 *
3204 * Update a single instruction with the vector in the stack, avoiding
3205 * dynamically allocated memory. This function should be used when it is
3206 * not possible to allocate memory for a vector. The single instruction
3207 * is patched in immediately.
3208 */
smp_text_poke_single(void * addr,const void * opcode,size_t len,const void * emulate)3209 void __ref smp_text_poke_single(void *addr, const void *opcode, size_t len, const void *emulate)
3210 {
3211 smp_text_poke_batch_add(addr, opcode, len, emulate);
3212 smp_text_poke_batch_finish();
3213 }
3214