xref: /linux/arch/riscv/kernel/traps.c (revision 69050f8d6d075dc01af7a5f2f550a8067510366f) 
1 // SPDX-License-Identifier: GPL-2.0-only
2 /*
3  * Copyright (C) 2012 Regents of the University of California
4  */
5 
6 #include <linux/cpu.h>
7 #include <linux/kernel.h>
8 #include <linux/init.h>
9 #include <linux/irqflags.h>
10 #include <linux/randomize_kstack.h>
11 #include <linux/sched.h>
12 #include <linux/sched/debug.h>
13 #include <linux/sched/signal.h>
14 #include <linux/signal.h>
15 #include <linux/kdebug.h>
16 #include <linux/uaccess.h>
17 #include <linux/kprobes.h>
18 #include <linux/uprobes.h>
19 #include <asm/uprobes.h>
20 #include <linux/mm.h>
21 #include <linux/module.h>
22 #include <linux/irq.h>
23 #include <linux/kexec.h>
24 #include <linux/entry-common.h>
25 
26 #include <asm/asm-prototypes.h>
27 #include <asm/bug.h>
28 #include <asm/cfi.h>
29 #include <asm/csr.h>
30 #include <asm/processor.h>
31 #include <asm/ptrace.h>
32 #include <asm/syscall.h>
33 #include <asm/thread_info.h>
34 #include <asm/vector.h>
35 #include <asm/irq_stack.h>
36 
37 int show_unhandled_signals = 1;
38 
39 static DEFINE_RAW_SPINLOCK(die_lock);
40 
41 static int copy_code(struct pt_regs *regs, u16 *val, const u16 *insns)
42 {
43 	const void __user *uaddr = (__force const void __user *)insns;
44 
45 	if (!user_mode(regs))
46 		return get_kernel_nofault(*val, insns);
47 
48 	/* The user space code from other tasks cannot be accessed. */
49 	if (regs != task_pt_regs(current))
50 		return -EPERM;
51 
52 	return copy_from_user_nofault(val, uaddr, sizeof(*val));
53 }
54 
55 static void dump_instr(const char *loglvl, struct pt_regs *regs)
56 {
57 	char str[sizeof("0000 ") * 12 + 2 + 1], *p = str;
58 	const u16 *insns = (u16 *)instruction_pointer(regs);
59 	long bad;
60 	u16 val;
61 	int i;
62 
63 	for (i = -10; i < 2; i++) {
64 		bad = copy_code(regs, &val, &insns[i]);
65 		if (!bad) {
66 			p += sprintf(p, i == 0 ? "(%04hx) " : "%04hx ", val);
67 		} else {
68 			printk("%sCode: Unable to access instruction at 0x%px.\n",
69 			       loglvl, &insns[i]);
70 			return;
71 		}
72 	}
73 	printk("%sCode: %s\n", loglvl, str);
74 }
75 
76 void die(struct pt_regs *regs, const char *str)
77 {
78 	static int die_counter;
79 	int ret;
80 	long cause;
81 	unsigned long flags;
82 
83 	oops_enter();
84 
85 	raw_spin_lock_irqsave(&die_lock, flags);
86 	console_verbose();
87 	bust_spinlocks(1);
88 
89 	pr_emerg("%s [#%d]\n", str, ++die_counter);
90 	print_modules();
91 	if (regs) {
92 		show_regs(regs);
93 		dump_instr(KERN_EMERG, regs);
94 	}
95 
96 	cause = regs ? regs->cause : -1;
97 	ret = notify_die(DIE_OOPS, str, regs, 0, cause, SIGSEGV);
98 
99 	if (kexec_should_crash(current))
100 		crash_kexec(regs);
101 
102 	bust_spinlocks(0);
103 	add_taint(TAINT_DIE, LOCKDEP_NOW_UNRELIABLE);
104 	raw_spin_unlock_irqrestore(&die_lock, flags);
105 	oops_exit();
106 
107 	if (in_interrupt())
108 		panic("Fatal exception in interrupt");
109 	if (panic_on_oops)
110 		panic("Fatal exception");
111 	if (ret != NOTIFY_STOP)
112 		make_task_dead(SIGSEGV);
113 }
114 
115 void do_trap(struct pt_regs *regs, int signo, int code, unsigned long addr)
116 {
117 	struct task_struct *tsk = current;
118 
119 	if (show_unhandled_signals && unhandled_signal(tsk, signo)
120 	    && printk_ratelimit()) {
121 		pr_info("%s[%d]: unhandled signal %d code 0x%x at 0x" REG_FMT,
122 			tsk->comm, task_pid_nr(tsk), signo, code, addr);
123 		print_vma_addr(KERN_CONT " in ", instruction_pointer(regs));
124 		pr_cont("\n");
125 		__show_regs(regs);
126 		dump_instr(KERN_INFO, regs);
127 	}
128 
129 	force_sig_fault(signo, code, (void __user *)addr);
130 }
131 
132 static void do_trap_error(struct pt_regs *regs, int signo, int code,
133 	unsigned long addr, const char *str)
134 {
135 	current->thread.bad_cause = regs->cause;
136 
137 	if (user_mode(regs)) {
138 		do_trap(regs, signo, code, addr);
139 	} else {
140 		if (!fixup_exception(regs))
141 			die(regs, str);
142 	}
143 }
144 
145 #if defined(CONFIG_XIP_KERNEL) && defined(CONFIG_RISCV_ALTERNATIVE)
146 #define __trap_section __noinstr_section(".xip.traps")
147 #else
148 #define __trap_section noinstr
149 #endif
150 #define DO_ERROR_INFO(name, signo, code, str)					\
151 asmlinkage __visible __trap_section void name(struct pt_regs *regs)		\
152 {										\
153 	if (user_mode(regs)) {							\
154 		irqentry_enter_from_user_mode(regs);				\
155 		local_irq_enable();						\
156 		do_trap_error(regs, signo, code, regs->epc, "Oops - " str);	\
157 		local_irq_disable();						\
158 		irqentry_exit_to_user_mode(regs);				\
159 	} else {								\
160 		irqentry_state_t state = irqentry_nmi_enter(regs);		\
161 		do_trap_error(regs, signo, code, regs->epc, "Oops - " str);	\
162 		irqentry_nmi_exit(regs, state);					\
163 	}									\
164 }
165 
166 DO_ERROR_INFO(do_trap_unknown,
167 	SIGILL, ILL_ILLTRP, "unknown exception");
168 DO_ERROR_INFO(do_trap_insn_misaligned,
169 	SIGBUS, BUS_ADRALN, "instruction address misaligned");
170 DO_ERROR_INFO(do_trap_insn_fault,
171 	SIGSEGV, SEGV_ACCERR, "instruction access fault");
172 
173 asmlinkage __visible __trap_section void do_trap_insn_illegal(struct pt_regs *regs)
174 {
175 	bool handled;
176 
177 	if (user_mode(regs)) {
178 		irqentry_enter_from_user_mode(regs);
179 		local_irq_enable();
180 
181 		handled = riscv_v_first_use_handler(regs);
182 		if (!handled)
183 			do_trap_error(regs, SIGILL, ILL_ILLOPC, regs->epc,
184 				      "Oops - illegal instruction");
185 
186 		local_irq_disable();
187 		irqentry_exit_to_user_mode(regs);
188 	} else {
189 		irqentry_state_t state = irqentry_nmi_enter(regs);
190 
191 		do_trap_error(regs, SIGILL, ILL_ILLOPC, regs->epc,
192 			      "Oops - illegal instruction");
193 
194 		irqentry_nmi_exit(regs, state);
195 	}
196 }
197 
198 DO_ERROR_INFO(do_trap_load_fault,
199 	SIGSEGV, SEGV_ACCERR, "load access fault");
200 
201 enum misaligned_access_type {
202 	MISALIGNED_STORE,
203 	MISALIGNED_LOAD,
204 };
205 static const struct {
206 	const char *type_str;
207 	int (*handler)(struct pt_regs *regs);
208 } misaligned_handler[] = {
209 	[MISALIGNED_STORE] = {
210 		.type_str = "Oops - store (or AMO) address misaligned",
211 		.handler = handle_misaligned_store,
212 	},
213 	[MISALIGNED_LOAD] = {
214 		.type_str = "Oops - load address misaligned",
215 		.handler = handle_misaligned_load,
216 	},
217 };
218 
219 static void do_trap_misaligned(struct pt_regs *regs, enum misaligned_access_type type)
220 {
221 	irqentry_state_t state;
222 
223 	if (user_mode(regs)) {
224 		irqentry_enter_from_user_mode(regs);
225 		local_irq_enable();
226 	} else {
227 		state = irqentry_nmi_enter(regs);
228 	}
229 
230 	if (misaligned_handler[type].handler(regs))
231 		do_trap_error(regs, SIGBUS, BUS_ADRALN, regs->epc,
232 			      misaligned_handler[type].type_str);
233 
234 	if (user_mode(regs)) {
235 		local_irq_disable();
236 		irqentry_exit_to_user_mode(regs);
237 	} else {
238 		irqentry_nmi_exit(regs, state);
239 	}
240 }
241 
242 asmlinkage __visible __trap_section void do_trap_load_misaligned(struct pt_regs *regs)
243 {
244 	do_trap_misaligned(regs, MISALIGNED_LOAD);
245 }
246 
247 asmlinkage __visible __trap_section void do_trap_store_misaligned(struct pt_regs *regs)
248 {
249 	do_trap_misaligned(regs, MISALIGNED_STORE);
250 }
251 
252 DO_ERROR_INFO(do_trap_store_fault,
253 	SIGSEGV, SEGV_ACCERR, "store (or AMO) access fault");
254 DO_ERROR_INFO(do_trap_ecall_s,
255 	SIGILL, ILL_ILLTRP, "environment call from S-mode");
256 DO_ERROR_INFO(do_trap_ecall_m,
257 	SIGILL, ILL_ILLTRP, "environment call from M-mode");
258 
259 static inline unsigned long get_break_insn_length(unsigned long pc)
260 {
261 	bug_insn_t insn;
262 
263 	if (get_kernel_nofault(insn, (bug_insn_t *)pc))
264 		return 0;
265 
266 	return GET_INSN_LENGTH(insn);
267 }
268 
269 static bool probe_single_step_handler(struct pt_regs *regs)
270 {
271 	bool user = user_mode(regs);
272 
273 	return user ? uprobe_single_step_handler(regs) : kprobe_single_step_handler(regs);
274 }
275 
276 static bool probe_breakpoint_handler(struct pt_regs *regs)
277 {
278 	bool user = user_mode(regs);
279 
280 	return user ? uprobe_breakpoint_handler(regs) : kprobe_breakpoint_handler(regs);
281 }
282 
283 void handle_break(struct pt_regs *regs)
284 {
285 	if (probe_single_step_handler(regs))
286 		return;
287 
288 	if (probe_breakpoint_handler(regs))
289 		return;
290 
291 	current->thread.bad_cause = regs->cause;
292 
293 	if (user_mode(regs))
294 		force_sig_fault(SIGTRAP, TRAP_BRKPT, (void __user *)regs->epc);
295 #ifdef CONFIG_KGDB
296 	else if (notify_die(DIE_TRAP, "EBREAK", regs, 0, regs->cause, SIGTRAP)
297 								== NOTIFY_STOP)
298 		return;
299 #endif
300 	else if (report_bug(regs->epc, regs) == BUG_TRAP_TYPE_WARN ||
301 		 handle_cfi_failure(regs) == BUG_TRAP_TYPE_WARN)
302 		regs->epc += get_break_insn_length(regs->epc);
303 	else
304 		die(regs, "Kernel BUG");
305 }
306 
307 asmlinkage __visible __trap_section void do_trap_break(struct pt_regs *regs)
308 {
309 	if (user_mode(regs)) {
310 		irqentry_enter_from_user_mode(regs);
311 		local_irq_enable();
312 
313 		handle_break(regs);
314 
315 		local_irq_disable();
316 		irqentry_exit_to_user_mode(regs);
317 	} else {
318 		irqentry_state_t state = irqentry_nmi_enter(regs);
319 
320 		handle_break(regs);
321 
322 		irqentry_nmi_exit(regs, state);
323 	}
324 }
325 
326 asmlinkage __visible __trap_section  __no_stack_protector
327 void do_trap_ecall_u(struct pt_regs *regs)
328 {
329 	if (user_mode(regs)) {
330 		long syscall = regs->a7;
331 
332 		regs->epc += 4;
333 		regs->orig_a0 = regs->a0;
334 		regs->a0 = -ENOSYS;
335 
336 		riscv_v_vstate_discard(regs);
337 
338 		syscall = syscall_enter_from_user_mode(regs, syscall);
339 
340 		add_random_kstack_offset();
341 
342 		if (syscall >= 0 && syscall < NR_syscalls) {
343 			syscall = array_index_nospec(syscall, NR_syscalls);
344 			syscall_handler(regs, syscall);
345 		}
346 
347 		/*
348 		 * Ultimately, this value will get limited by KSTACK_OFFSET_MAX(),
349 		 * so the maximum stack offset is 1k bytes (10 bits).
350 		 *
351 		 * The actual entropy will be further reduced by the compiler when
352 		 * applying stack alignment constraints: 16-byte (i.e. 4-bit) aligned
353 		 * for RV32I or RV64I.
354 		 *
355 		 * The resulting 6 bits of entropy is seen in SP[9:4].
356 		 */
357 		choose_random_kstack_offset(get_random_u16());
358 
359 		syscall_exit_to_user_mode(regs);
360 	} else {
361 		irqentry_state_t state = irqentry_nmi_enter(regs);
362 
363 		do_trap_error(regs, SIGILL, ILL_ILLTRP, regs->epc,
364 			"Oops - environment call from U-mode");
365 
366 		irqentry_nmi_exit(regs, state);
367 	}
368 
369 }
370 
371 #define CFI_TVAL_FCFI_CODE	2
372 #define CFI_TVAL_BCFI_CODE	3
373 /* handle cfi violations */
374 bool handle_user_cfi_violation(struct pt_regs *regs)
375 {
376 	unsigned long tval = csr_read(CSR_TVAL);
377 	bool is_fcfi = (tval == CFI_TVAL_FCFI_CODE && cpu_supports_indirect_br_lp_instr());
378 	bool is_bcfi = (tval == CFI_TVAL_BCFI_CODE && cpu_supports_shadow_stack());
379 
380 	/*
381 	 * Handle uprobe event first. The probe point can be a valid target
382 	 * of indirect jumps or calls, in this case, forward cfi violation
383 	 * will be triggered instead of breakpoint exception. Clear ELP flag
384 	 * on sstatus image as well to avoid recurring fault.
385 	 */
386 	if (is_fcfi && probe_breakpoint_handler(regs)) {
387 		regs->status &= ~SR_ELP;
388 		return true;
389 	}
390 
391 	if (is_fcfi || is_bcfi) {
392 		do_trap_error(regs, SIGSEGV, SEGV_CPERR, regs->epc,
393 			      "Oops - control flow violation");
394 		return true;
395 	}
396 
397 	return false;
398 }
399 
400 /*
401  * software check exception is defined with risc-v cfi spec. Software check
402  * exception is raised when:
403  * a) An indirect branch doesn't land on 4 byte aligned PC or `lpad`
404  *    instruction or `label` value programmed in `lpad` instr doesn't
405  *    match with value setup in `x7`. reported code in `xtval` is 2.
406  * b) `sspopchk` instruction finds a mismatch between top of shadow stack (ssp)
407  *    and x1/x5. reported code in `xtval` is 3.
408  */
409 asmlinkage __visible __trap_section void do_trap_software_check(struct pt_regs *regs)
410 {
411 	if (user_mode(regs)) {
412 		irqentry_enter_from_user_mode(regs);
413 
414 		/* not a cfi violation, then merge into flow of unknown trap handler */
415 		if (!handle_user_cfi_violation(regs))
416 			do_trap_unknown(regs);
417 
418 		irqentry_exit_to_user_mode(regs);
419 	} else {
420 		/* sw check exception coming from kernel is a bug in kernel */
421 		die(regs, "Kernel BUG");
422 	}
423 }
424 
425 #ifdef CONFIG_MMU
426 asmlinkage __visible noinstr void do_page_fault(struct pt_regs *regs)
427 {
428 	irqentry_state_t state = irqentry_enter(regs);
429 
430 	handle_page_fault(regs);
431 
432 	local_irq_disable();
433 
434 	irqentry_exit(regs, state);
435 }
436 #endif
437 
438 static void noinstr handle_riscv_irq(struct pt_regs *regs)
439 {
440 	struct pt_regs *old_regs;
441 
442 	irq_enter_rcu();
443 	old_regs = set_irq_regs(regs);
444 	handle_arch_irq(regs);
445 	set_irq_regs(old_regs);
446 	irq_exit_rcu();
447 }
448 
449 asmlinkage void noinstr do_irq(struct pt_regs *regs)
450 {
451 	irqentry_state_t state = irqentry_enter(regs);
452 
453 	if (IS_ENABLED(CONFIG_IRQ_STACKS) && on_thread_stack())
454 		call_on_irq_stack(regs, handle_riscv_irq);
455 	else
456 		handle_riscv_irq(regs);
457 
458 	irqentry_exit(regs, state);
459 }
460 
461 #ifdef CONFIG_GENERIC_BUG
462 int is_valid_bugaddr(unsigned long pc)
463 {
464 	bug_insn_t insn;
465 
466 	if (pc < VMALLOC_START)
467 		return 0;
468 	if (get_kernel_nofault(insn, (bug_insn_t *)pc))
469 		return 0;
470 	if ((insn & __INSN_LENGTH_MASK) == __INSN_LENGTH_32)
471 		return (insn == __BUG_INSN_32);
472 	else
473 		return ((insn & __COMPRESSED_INSN_MASK) == __BUG_INSN_16);
474 }
475 #endif /* CONFIG_GENERIC_BUG */
476 
477 #ifdef CONFIG_VMAP_STACK
478 DEFINE_PER_CPU(unsigned long [OVERFLOW_STACK_SIZE/sizeof(long)],
479 		overflow_stack)__aligned(16);
480 
481 asmlinkage void handle_bad_stack(struct pt_regs *regs)
482 {
483 	unsigned long tsk_stk = (unsigned long)current->stack;
484 	unsigned long ovf_stk = (unsigned long)this_cpu_ptr(overflow_stack);
485 
486 	console_verbose();
487 
488 	pr_emerg("Insufficient stack space to handle exception!\n");
489 	pr_emerg("Task stack:     [0x%016lx..0x%016lx]\n",
490 			tsk_stk, tsk_stk + THREAD_SIZE);
491 	pr_emerg("Overflow stack: [0x%016lx..0x%016lx]\n",
492 			ovf_stk, ovf_stk + OVERFLOW_STACK_SIZE);
493 
494 	__show_regs(regs);
495 	panic("Kernel stack overflow");
496 
497 	for (;;)
498 		wait_for_interrupt();
499 }
500 #endif
501