1 // SPDX-License-Identifier: GPL-2.0-or-later
2 /*
3 *
4 * Copyright (C) 2007 Alan Stern
5 * Copyright (C) 2009 IBM Corporation
6 * Copyright (C) 2009 Frederic Weisbecker <fweisbec@gmail.com>
7 *
8 * Authors: Alan Stern <stern@rowland.harvard.edu>
9 * K.Prasad <prasad@linux.vnet.ibm.com>
10 * Frederic Weisbecker <fweisbec@gmail.com>
11 */
12
13 /*
14 * HW_breakpoint: a unified kernel/user-space hardware breakpoint facility,
15 * using the CPU's debug registers.
16 */
17
18 #include <linux/perf_event.h>
19 #include <linux/hw_breakpoint.h>
20 #include <linux/irqflags.h>
21 #include <linux/notifier.h>
22 #include <linux/kallsyms.h>
23 #include <linux/kprobes.h>
24 #include <linux/percpu.h>
25 #include <linux/kdebug.h>
26 #include <linux/kernel.h>
27 #include <linux/export.h>
28 #include <linux/sched.h>
29 #include <linux/smp.h>
30
31 #include <asm/hw_breakpoint.h>
32 #include <asm/processor.h>
33 #include <asm/debugreg.h>
34 #include <asm/user.h>
35 #include <asm/desc.h>
36 #include <asm/tlbflush.h>
37
38 /* Per cpu debug control register value */
39 DEFINE_PER_CPU(unsigned long, cpu_dr7);
40 EXPORT_PER_CPU_SYMBOL(cpu_dr7);
41
42 /* Per cpu debug address registers values */
43 static DEFINE_PER_CPU(unsigned long, cpu_debugreg[HBP_NUM]);
44
45 /*
46 * Stores the breakpoints currently in use on each breakpoint address
47 * register for each cpus
48 */
49 static DEFINE_PER_CPU(struct perf_event *, bp_per_reg[HBP_NUM]);
50
51
52 static inline unsigned long
__encode_dr7(int drnum,unsigned int len,unsigned int type)53 __encode_dr7(int drnum, unsigned int len, unsigned int type)
54 {
55 unsigned long bp_info;
56
57 bp_info = (len | type) & 0xf;
58 bp_info <<= (DR_CONTROL_SHIFT + drnum * DR_CONTROL_SIZE);
59 bp_info |= (DR_GLOBAL_ENABLE << (drnum * DR_ENABLE_SIZE));
60
61 return bp_info;
62 }
63
64 /*
65 * Encode the length, type, Exact, and Enable bits for a particular breakpoint
66 * as stored in debug register 7.
67 */
encode_dr7(int drnum,unsigned int len,unsigned int type)68 unsigned long encode_dr7(int drnum, unsigned int len, unsigned int type)
69 {
70 return __encode_dr7(drnum, len, type) | DR_GLOBAL_SLOWDOWN;
71 }
72
73 /*
74 * Decode the length and type bits for a particular breakpoint as
75 * stored in debug register 7. Return the "enabled" status.
76 */
decode_dr7(unsigned long dr7,int bpnum,unsigned * len,unsigned * type)77 int decode_dr7(unsigned long dr7, int bpnum, unsigned *len, unsigned *type)
78 {
79 int bp_info = dr7 >> (DR_CONTROL_SHIFT + bpnum * DR_CONTROL_SIZE);
80
81 *len = (bp_info & 0xc) | 0x40;
82 *type = (bp_info & 0x3) | 0x80;
83
84 return (dr7 >> (bpnum * DR_ENABLE_SIZE)) & 0x3;
85 }
86
87 /*
88 * Install a perf counter breakpoint.
89 *
90 * We seek a free debug address register and use it for this
91 * breakpoint. Eventually we enable it in the debug control register.
92 *
93 * Atomic: we hold the counter->ctx->lock and we only handle variables
94 * and registers local to this cpu.
95 */
arch_install_hw_breakpoint(struct perf_event * bp)96 int arch_install_hw_breakpoint(struct perf_event *bp)
97 {
98 struct arch_hw_breakpoint *info = counter_arch_bp(bp);
99 unsigned long *dr7;
100 int i;
101
102 lockdep_assert_irqs_disabled();
103
104 for (i = 0; i < HBP_NUM; i++) {
105 struct perf_event **slot = this_cpu_ptr(&bp_per_reg[i]);
106
107 if (!*slot) {
108 *slot = bp;
109 break;
110 }
111 }
112
113 if (WARN_ONCE(i == HBP_NUM, "Can't find any breakpoint slot"))
114 return -EBUSY;
115
116 set_debugreg(info->address, i);
117 __this_cpu_write(cpu_debugreg[i], info->address);
118
119 dr7 = this_cpu_ptr(&cpu_dr7);
120 *dr7 |= encode_dr7(i, info->len, info->type);
121
122 /*
123 * Ensure we first write cpu_dr7 before we set the DR7 register.
124 * This ensures an NMI never see cpu_dr7 0 when DR7 is not.
125 */
126 barrier();
127
128 set_debugreg(*dr7, 7);
129 if (info->mask)
130 amd_set_dr_addr_mask(info->mask, i);
131
132 return 0;
133 }
134
135 /*
136 * Uninstall the breakpoint contained in the given counter.
137 *
138 * First we search the debug address register it uses and then we disable
139 * it.
140 *
141 * Atomic: we hold the counter->ctx->lock and we only handle variables
142 * and registers local to this cpu.
143 */
arch_uninstall_hw_breakpoint(struct perf_event * bp)144 void arch_uninstall_hw_breakpoint(struct perf_event *bp)
145 {
146 struct arch_hw_breakpoint *info = counter_arch_bp(bp);
147 unsigned long dr7;
148 int i;
149
150 lockdep_assert_irqs_disabled();
151
152 for (i = 0; i < HBP_NUM; i++) {
153 struct perf_event **slot = this_cpu_ptr(&bp_per_reg[i]);
154
155 if (*slot == bp) {
156 *slot = NULL;
157 break;
158 }
159 }
160
161 if (WARN_ONCE(i == HBP_NUM, "Can't find any breakpoint slot"))
162 return;
163
164 dr7 = this_cpu_read(cpu_dr7);
165 dr7 &= ~__encode_dr7(i, info->len, info->type);
166
167 set_debugreg(dr7, 7);
168 if (info->mask)
169 amd_set_dr_addr_mask(0, i);
170
171 /*
172 * Ensure the write to cpu_dr7 is after we've set the DR7 register.
173 * This ensures an NMI never see cpu_dr7 0 when DR7 is not.
174 */
175 barrier();
176
177 this_cpu_write(cpu_dr7, dr7);
178 }
179
arch_bp_generic_len(int x86_len)180 static int arch_bp_generic_len(int x86_len)
181 {
182 switch (x86_len) {
183 case X86_BREAKPOINT_LEN_1:
184 return HW_BREAKPOINT_LEN_1;
185 case X86_BREAKPOINT_LEN_2:
186 return HW_BREAKPOINT_LEN_2;
187 case X86_BREAKPOINT_LEN_4:
188 return HW_BREAKPOINT_LEN_4;
189 #ifdef CONFIG_X86_64
190 case X86_BREAKPOINT_LEN_8:
191 return HW_BREAKPOINT_LEN_8;
192 #endif
193 default:
194 return -EINVAL;
195 }
196 }
197
arch_bp_generic_fields(int x86_len,int x86_type,int * gen_len,int * gen_type)198 int arch_bp_generic_fields(int x86_len, int x86_type,
199 int *gen_len, int *gen_type)
200 {
201 int len;
202
203 /* Type */
204 switch (x86_type) {
205 case X86_BREAKPOINT_EXECUTE:
206 if (x86_len != X86_BREAKPOINT_LEN_X)
207 return -EINVAL;
208
209 *gen_type = HW_BREAKPOINT_X;
210 *gen_len = sizeof(long);
211 return 0;
212 case X86_BREAKPOINT_WRITE:
213 *gen_type = HW_BREAKPOINT_W;
214 break;
215 case X86_BREAKPOINT_RW:
216 *gen_type = HW_BREAKPOINT_W | HW_BREAKPOINT_R;
217 break;
218 default:
219 return -EINVAL;
220 }
221
222 /* Len */
223 len = arch_bp_generic_len(x86_len);
224 if (len < 0)
225 return -EINVAL;
226 *gen_len = len;
227
228 return 0;
229 }
230
231 /*
232 * Check for virtual address in kernel space.
233 */
arch_check_bp_in_kernelspace(struct arch_hw_breakpoint * hw)234 int arch_check_bp_in_kernelspace(struct arch_hw_breakpoint *hw)
235 {
236 unsigned long va;
237 int len;
238
239 va = hw->address;
240 len = arch_bp_generic_len(hw->len);
241 WARN_ON_ONCE(len < 0);
242
243 /*
244 * We don't need to worry about va + len - 1 overflowing:
245 * we already require that va is aligned to a multiple of len.
246 */
247 return (va >= TASK_SIZE_MAX) || ((va + len - 1) >= TASK_SIZE_MAX);
248 }
249
250 /*
251 * Checks whether the range [addr, end], overlaps the area [base, base + size).
252 */
within_area(unsigned long addr,unsigned long end,unsigned long base,unsigned long size)253 static inline bool within_area(unsigned long addr, unsigned long end,
254 unsigned long base, unsigned long size)
255 {
256 return end >= base && addr < (base + size);
257 }
258
259 /*
260 * Checks whether the range from addr to end, inclusive, overlaps the fixed
261 * mapped CPU entry area range or other ranges used for CPU entry.
262 */
within_cpu_entry(unsigned long addr,unsigned long end)263 static inline bool within_cpu_entry(unsigned long addr, unsigned long end)
264 {
265 int cpu;
266
267 /* CPU entry erea is always used for CPU entry */
268 if (within_area(addr, end, CPU_ENTRY_AREA_BASE,
269 CPU_ENTRY_AREA_MAP_SIZE))
270 return true;
271
272 /*
273 * When FSGSBASE is enabled, paranoid_entry() fetches the per-CPU
274 * GSBASE value via __per_cpu_offset or pcpu_unit_offsets.
275 */
276 #ifdef CONFIG_SMP
277 if (within_area(addr, end, (unsigned long)__per_cpu_offset,
278 sizeof(unsigned long) * nr_cpu_ids))
279 return true;
280 #else
281 if (within_area(addr, end, (unsigned long)&pcpu_unit_offsets,
282 sizeof(pcpu_unit_offsets)))
283 return true;
284 #endif
285
286 for_each_possible_cpu(cpu) {
287 /* The original rw GDT is being used after load_direct_gdt() */
288 if (within_area(addr, end, (unsigned long)get_cpu_gdt_rw(cpu),
289 GDT_SIZE))
290 return true;
291
292 /*
293 * cpu_tss_rw is not directly referenced by hardware, but
294 * cpu_tss_rw is also used in CPU entry code,
295 */
296 if (within_area(addr, end,
297 (unsigned long)&per_cpu(cpu_tss_rw, cpu),
298 sizeof(struct tss_struct)))
299 return true;
300
301 /*
302 * cpu_tlbstate.user_pcid_flush_mask is used for CPU entry.
303 * If a data breakpoint on it, it will cause an unwanted #DB.
304 * Protect the full cpu_tlbstate structure to be sure.
305 */
306 if (within_area(addr, end,
307 (unsigned long)&per_cpu(cpu_tlbstate, cpu),
308 sizeof(struct tlb_state)))
309 return true;
310
311 /*
312 * When in guest (X86_FEATURE_HYPERVISOR), local_db_save()
313 * will read per-cpu cpu_dr7 before clear dr7 register.
314 */
315 if (within_area(addr, end, (unsigned long)&per_cpu(cpu_dr7, cpu),
316 sizeof(cpu_dr7)))
317 return true;
318 }
319
320 return false;
321 }
322
arch_build_bp_info(struct perf_event * bp,const struct perf_event_attr * attr,struct arch_hw_breakpoint * hw)323 static int arch_build_bp_info(struct perf_event *bp,
324 const struct perf_event_attr *attr,
325 struct arch_hw_breakpoint *hw)
326 {
327 unsigned long bp_end;
328
329 bp_end = attr->bp_addr + attr->bp_len - 1;
330 if (bp_end < attr->bp_addr)
331 return -EINVAL;
332
333 /*
334 * Prevent any breakpoint of any type that overlaps the CPU
335 * entry area and data. This protects the IST stacks and also
336 * reduces the chance that we ever find out what happens if
337 * there's a data breakpoint on the GDT, IDT, or TSS.
338 */
339 if (within_cpu_entry(attr->bp_addr, bp_end))
340 return -EINVAL;
341
342 hw->address = attr->bp_addr;
343 hw->mask = 0;
344
345 /* Type */
346 switch (attr->bp_type) {
347 case HW_BREAKPOINT_W:
348 hw->type = X86_BREAKPOINT_WRITE;
349 break;
350 case HW_BREAKPOINT_W | HW_BREAKPOINT_R:
351 hw->type = X86_BREAKPOINT_RW;
352 break;
353 case HW_BREAKPOINT_X:
354 /*
355 * We don't allow kernel breakpoints in places that are not
356 * acceptable for kprobes. On non-kprobes kernels, we don't
357 * allow kernel breakpoints at all.
358 */
359 if (attr->bp_addr >= TASK_SIZE_MAX) {
360 if (within_kprobe_blacklist(attr->bp_addr))
361 return -EINVAL;
362 }
363
364 hw->type = X86_BREAKPOINT_EXECUTE;
365 /*
366 * x86 inst breakpoints need to have a specific undefined len.
367 * But we still need to check userspace is not trying to setup
368 * an unsupported length, to get a range breakpoint for example.
369 */
370 if (attr->bp_len == sizeof(long)) {
371 hw->len = X86_BREAKPOINT_LEN_X;
372 return 0;
373 }
374 fallthrough;
375 default:
376 return -EINVAL;
377 }
378
379 /* Len */
380 switch (attr->bp_len) {
381 case HW_BREAKPOINT_LEN_1:
382 hw->len = X86_BREAKPOINT_LEN_1;
383 break;
384 case HW_BREAKPOINT_LEN_2:
385 hw->len = X86_BREAKPOINT_LEN_2;
386 break;
387 case HW_BREAKPOINT_LEN_4:
388 hw->len = X86_BREAKPOINT_LEN_4;
389 break;
390 #ifdef CONFIG_X86_64
391 case HW_BREAKPOINT_LEN_8:
392 hw->len = X86_BREAKPOINT_LEN_8;
393 break;
394 #endif
395 default:
396 /* AMD range breakpoint */
397 if (!is_power_of_2(attr->bp_len))
398 return -EINVAL;
399 if (attr->bp_addr & (attr->bp_len - 1))
400 return -EINVAL;
401
402 if (!boot_cpu_has(X86_FEATURE_BPEXT))
403 return -EOPNOTSUPP;
404
405 /*
406 * It's impossible to use a range breakpoint to fake out
407 * user vs kernel detection because bp_len - 1 can't
408 * have the high bit set. If we ever allow range instruction
409 * breakpoints, then we'll have to check for kprobe-blacklisted
410 * addresses anywhere in the range.
411 */
412 hw->mask = attr->bp_len - 1;
413 hw->len = X86_BREAKPOINT_LEN_1;
414 }
415
416 return 0;
417 }
418
419 /*
420 * Validate the arch-specific HW Breakpoint register settings
421 */
hw_breakpoint_arch_parse(struct perf_event * bp,const struct perf_event_attr * attr,struct arch_hw_breakpoint * hw)422 int hw_breakpoint_arch_parse(struct perf_event *bp,
423 const struct perf_event_attr *attr,
424 struct arch_hw_breakpoint *hw)
425 {
426 unsigned int align;
427 int ret;
428
429
430 ret = arch_build_bp_info(bp, attr, hw);
431 if (ret)
432 return ret;
433
434 switch (hw->len) {
435 case X86_BREAKPOINT_LEN_1:
436 align = 0;
437 if (hw->mask)
438 align = hw->mask;
439 break;
440 case X86_BREAKPOINT_LEN_2:
441 align = 1;
442 break;
443 case X86_BREAKPOINT_LEN_4:
444 align = 3;
445 break;
446 #ifdef CONFIG_X86_64
447 case X86_BREAKPOINT_LEN_8:
448 align = 7;
449 break;
450 #endif
451 default:
452 WARN_ON_ONCE(1);
453 return -EINVAL;
454 }
455
456 /*
457 * Check that the low-order bits of the address are appropriate
458 * for the alignment implied by len.
459 */
460 if (hw->address & align)
461 return -EINVAL;
462
463 return 0;
464 }
465
466 /*
467 * Release the user breakpoints used by ptrace
468 */
flush_ptrace_hw_breakpoint(struct task_struct * tsk)469 void flush_ptrace_hw_breakpoint(struct task_struct *tsk)
470 {
471 int i;
472 struct thread_struct *t = &tsk->thread;
473
474 for (i = 0; i < HBP_NUM; i++) {
475 unregister_hw_breakpoint(t->ptrace_bps[i]);
476 t->ptrace_bps[i] = NULL;
477 }
478
479 t->virtual_dr6 = 0;
480 t->ptrace_dr7 = 0;
481 }
482
hw_breakpoint_restore(void)483 void hw_breakpoint_restore(void)
484 {
485 set_debugreg(__this_cpu_read(cpu_debugreg[0]), 0);
486 set_debugreg(__this_cpu_read(cpu_debugreg[1]), 1);
487 set_debugreg(__this_cpu_read(cpu_debugreg[2]), 2);
488 set_debugreg(__this_cpu_read(cpu_debugreg[3]), 3);
489 set_debugreg(DR6_RESERVED, 6);
490 set_debugreg(__this_cpu_read(cpu_dr7), 7);
491 }
492 EXPORT_SYMBOL_GPL(hw_breakpoint_restore);
493
494 /*
495 * Handle debug exception notifications.
496 *
497 * Return value is either NOTIFY_STOP or NOTIFY_DONE as explained below.
498 *
499 * NOTIFY_DONE returned if one of the following conditions is true.
500 * i) When the causative address is from user-space and the exception
501 * is a valid one, i.e. not triggered as a result of lazy debug register
502 * switching
503 * ii) When there are more bits than trap<n> set in DR6 register (such
504 * as BD, BS or BT) indicating that more than one debug condition is
505 * met and requires some more action in do_debug().
506 *
507 * NOTIFY_STOP returned for all other cases
508 *
509 */
hw_breakpoint_handler(struct die_args * args)510 static int hw_breakpoint_handler(struct die_args *args)
511 {
512 int i, rc = NOTIFY_STOP;
513 struct perf_event *bp;
514 unsigned long *dr6_p;
515 unsigned long dr6;
516 bool bpx;
517
518 /* The DR6 value is pointed by args->err */
519 dr6_p = (unsigned long *)ERR_PTR(args->err);
520 dr6 = *dr6_p;
521
522 /* Do an early return if no trap bits are set in DR6 */
523 if ((dr6 & DR_TRAP_BITS) == 0)
524 return NOTIFY_DONE;
525
526 /* Handle all the breakpoints that were triggered */
527 for (i = 0; i < HBP_NUM; ++i) {
528 if (likely(!(dr6 & (DR_TRAP0 << i))))
529 continue;
530
531 bp = this_cpu_read(bp_per_reg[i]);
532 if (!bp)
533 continue;
534
535 bpx = bp->hw.info.type == X86_BREAKPOINT_EXECUTE;
536
537 /*
538 * TF and data breakpoints are traps and can be merged, however
539 * instruction breakpoints are faults and will be raised
540 * separately.
541 *
542 * However DR6 can indicate both TF and instruction
543 * breakpoints. In that case take TF as that has precedence and
544 * delay the instruction breakpoint for the next exception.
545 */
546 if (bpx && (dr6 & DR_STEP))
547 continue;
548
549 /*
550 * Reset the 'i'th TRAP bit in dr6 to denote completion of
551 * exception handling
552 */
553 (*dr6_p) &= ~(DR_TRAP0 << i);
554
555 perf_bp_event(bp, args->regs);
556
557 /*
558 * Set up resume flag to avoid breakpoint recursion when
559 * returning back to origin.
560 */
561 if (bpx)
562 args->regs->flags |= X86_EFLAGS_RF;
563 }
564
565 /*
566 * Further processing in do_debug() is needed for a) user-space
567 * breakpoints (to generate signals) and b) when the system has
568 * taken exception due to multiple causes
569 */
570 if ((current->thread.virtual_dr6 & DR_TRAP_BITS) ||
571 (dr6 & (~DR_TRAP_BITS)))
572 rc = NOTIFY_DONE;
573
574 return rc;
575 }
576
577 /*
578 * Handle debug exception notifications.
579 */
hw_breakpoint_exceptions_notify(struct notifier_block * unused,unsigned long val,void * data)580 int hw_breakpoint_exceptions_notify(
581 struct notifier_block *unused, unsigned long val, void *data)
582 {
583 if (val != DIE_DEBUG)
584 return NOTIFY_DONE;
585
586 return hw_breakpoint_handler(data);
587 }
588
hw_breakpoint_pmu_read(struct perf_event * bp)589 void hw_breakpoint_pmu_read(struct perf_event *bp)
590 {
591 /* TODO */
592 }
593