xref: /linux/arch/riscv/kernel/traps.c (revision 7a5f1cd22d47f8ca4b760b6334378ae42c1bd24b) 
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 #define __trap_section noinstr
146 #define DO_ERROR_INFO(name, signo, code, str)					\
147 asmlinkage __visible __trap_section void name(struct pt_regs *regs)		\
148 {										\
149 	if (user_mode(regs)) {							\
150 		irqentry_enter_from_user_mode(regs);				\
151 		local_irq_enable();						\
152 		do_trap_error(regs, signo, code, regs->epc, "Oops - " str);	\
153 		local_irq_disable();						\
154 		irqentry_exit_to_user_mode(regs);				\
155 	} else {								\
156 		irqentry_state_t state = irqentry_nmi_enter(regs);		\
157 		do_trap_error(regs, signo, code, regs->epc, "Oops - " str);	\
158 		irqentry_nmi_exit(regs, state);					\
159 	}									\
160 }
161 
162 DO_ERROR_INFO(do_trap_unknown,
163 	SIGILL, ILL_ILLTRP, "unknown exception");
164 DO_ERROR_INFO(do_trap_hardware_error,
165 	SIGBUS, BUS_MCEERR_AR, "hardware error");
166 DO_ERROR_INFO(do_trap_insn_misaligned,
167 	SIGBUS, BUS_ADRALN, "instruction address misaligned");
168 DO_ERROR_INFO(do_trap_insn_fault,
169 	SIGSEGV, SEGV_ACCERR, "instruction access fault");
170 
171 asmlinkage __visible __trap_section void do_trap_insn_illegal(struct pt_regs *regs)
172 {
173 	bool handled;
174 
175 	if (user_mode(regs)) {
176 		irqentry_enter_from_user_mode(regs);
177 		local_irq_enable();
178 
179 		handled = riscv_v_first_use_handler(regs);
180 		if (!handled)
181 			do_trap_error(regs, SIGILL, ILL_ILLOPC, regs->epc,
182 				      "Oops - illegal instruction");
183 
184 		local_irq_disable();
185 		irqentry_exit_to_user_mode(regs);
186 	} else {
187 		irqentry_state_t state = irqentry_nmi_enter(regs);
188 
189 		do_trap_error(regs, SIGILL, ILL_ILLOPC, regs->epc,
190 			      "Oops - illegal instruction");
191 
192 		irqentry_nmi_exit(regs, state);
193 	}
194 }
195 
196 DO_ERROR_INFO(do_trap_load_fault,
197 	SIGSEGV, SEGV_ACCERR, "load access fault");
198 
199 enum misaligned_access_type {
200 	MISALIGNED_STORE,
201 	MISALIGNED_LOAD,
202 };
203 static const struct {
204 	const char *type_str;
205 	int (*handler)(struct pt_regs *regs);
206 } misaligned_handler[] = {
207 	[MISALIGNED_STORE] = {
208 		.type_str = "Oops - store (or AMO) address misaligned",
209 		.handler = handle_misaligned_store,
210 	},
211 	[MISALIGNED_LOAD] = {
212 		.type_str = "Oops - load address misaligned",
213 		.handler = handle_misaligned_load,
214 	},
215 };
216 
217 static void do_trap_misaligned(struct pt_regs *regs, enum misaligned_access_type type)
218 {
219 	irqentry_state_t state;
220 
221 	if (user_mode(regs)) {
222 		irqentry_enter_from_user_mode(regs);
223 		local_irq_enable();
224 	} else {
225 		state = irqentry_nmi_enter(regs);
226 	}
227 
228 	if (misaligned_handler[type].handler(regs))
229 		do_trap_error(regs, SIGBUS, BUS_ADRALN, regs->epc,
230 			      misaligned_handler[type].type_str);
231 
232 	if (user_mode(regs)) {
233 		local_irq_disable();
234 		irqentry_exit_to_user_mode(regs);
235 	} else {
236 		irqentry_nmi_exit(regs, state);
237 	}
238 }
239 
240 asmlinkage __visible __trap_section void do_trap_load_misaligned(struct pt_regs *regs)
241 {
242 	do_trap_misaligned(regs, MISALIGNED_LOAD);
243 }
244 
245 asmlinkage __visible __trap_section void do_trap_store_misaligned(struct pt_regs *regs)
246 {
247 	do_trap_misaligned(regs, MISALIGNED_STORE);
248 }
249 
250 DO_ERROR_INFO(do_trap_store_fault,
251 	SIGSEGV, SEGV_ACCERR, "store (or AMO) access fault");
252 DO_ERROR_INFO(do_trap_ecall_s,
253 	SIGILL, ILL_ILLTRP, "environment call from S-mode");
254 DO_ERROR_INFO(do_trap_ecall_m,
255 	SIGILL, ILL_ILLTRP, "environment call from M-mode");
256 
257 static inline unsigned long get_break_insn_length(unsigned long pc)
258 {
259 	bug_insn_t insn;
260 
261 	if (get_kernel_nofault(insn, (bug_insn_t *)pc))
262 		return 0;
263 
264 	return GET_INSN_LENGTH(insn);
265 }
266 
267 static bool probe_single_step_handler(struct pt_regs *regs)
268 {
269 	bool user = user_mode(regs);
270 
271 	return user ? uprobe_single_step_handler(regs) : kprobe_single_step_handler(regs);
272 }
273 
274 static bool probe_breakpoint_handler(struct pt_regs *regs)
275 {
276 	bool user = user_mode(regs);
277 
278 	return user ? uprobe_breakpoint_handler(regs) : kprobe_breakpoint_handler(regs);
279 }
280 
281 void handle_break(struct pt_regs *regs)
282 {
283 	if (probe_single_step_handler(regs))
284 		return;
285 
286 	if (probe_breakpoint_handler(regs))
287 		return;
288 
289 	current->thread.bad_cause = regs->cause;
290 
291 	if (user_mode(regs))
292 		force_sig_fault(SIGTRAP, TRAP_BRKPT, (void __user *)regs->epc);
293 #ifdef CONFIG_KGDB
294 	else if (notify_die(DIE_TRAP, "EBREAK", regs, 0, regs->cause, SIGTRAP)
295 								== NOTIFY_STOP)
296 		return;
297 #endif
298 	else if (report_bug(regs->epc, regs) == BUG_TRAP_TYPE_WARN ||
299 		 handle_cfi_failure(regs) == BUG_TRAP_TYPE_WARN)
300 		regs->epc += get_break_insn_length(regs->epc);
301 	else
302 		die(regs, "Kernel BUG");
303 }
304 
305 asmlinkage __visible __trap_section void do_trap_break(struct pt_regs *regs)
306 {
307 	if (user_mode(regs)) {
308 		irqentry_enter_from_user_mode(regs);
309 		local_irq_enable();
310 
311 		handle_break(regs);
312 
313 		local_irq_disable();
314 		irqentry_exit_to_user_mode(regs);
315 	} else {
316 		irqentry_state_t state = irqentry_nmi_enter(regs);
317 
318 		handle_break(regs);
319 
320 		irqentry_nmi_exit(regs, state);
321 	}
322 }
323 
324 asmlinkage __visible __trap_section  __no_stack_protector
325 void do_trap_ecall_u(struct pt_regs *regs)
326 {
327 	if (user_mode(regs)) {
328 		long syscall = regs->a7;
329 
330 		regs->epc += 4;
331 		regs->orig_a0 = regs->a0;
332 		regs->a0 = -ENOSYS;
333 
334 		riscv_v_vstate_discard(regs);
335 
336 		syscall = syscall_enter_from_user_mode(regs, syscall);
337 
338 		add_random_kstack_offset();
339 
340 		if (syscall >= 0 && syscall < NR_syscalls) {
341 			syscall = array_index_nospec(syscall, NR_syscalls);
342 			syscall_handler(regs, syscall);
343 		}
344 
345 		syscall_exit_to_user_mode(regs);
346 	} else {
347 		irqentry_state_t state = irqentry_nmi_enter(regs);
348 
349 		do_trap_error(regs, SIGILL, ILL_ILLTRP, regs->epc,
350 			"Oops - environment call from U-mode");
351 
352 		irqentry_nmi_exit(regs, state);
353 	}
354 
355 }
356 
357 #define CFI_TVAL_FCFI_CODE	2
358 #define CFI_TVAL_BCFI_CODE	3
359 /* handle cfi violations */
360 bool handle_user_cfi_violation(struct pt_regs *regs)
361 {
362 	unsigned long tval = csr_read(CSR_TVAL);
363 	bool is_fcfi = (tval == CFI_TVAL_FCFI_CODE && cpu_supports_indirect_br_lp_instr());
364 	bool is_bcfi = (tval == CFI_TVAL_BCFI_CODE && cpu_supports_shadow_stack());
365 
366 	/*
367 	 * Handle uprobe event first. The probe point can be a valid target
368 	 * of indirect jumps or calls, in this case, forward cfi violation
369 	 * will be triggered instead of breakpoint exception. Clear ELP flag
370 	 * on sstatus image as well to avoid recurring fault.
371 	 */
372 	if (is_fcfi && probe_breakpoint_handler(regs)) {
373 		regs->status &= ~SR_ELP;
374 		return true;
375 	}
376 
377 	if (is_fcfi || is_bcfi) {
378 		do_trap_error(regs, SIGSEGV, SEGV_CPERR, regs->epc,
379 			      "Oops - control flow violation");
380 		return true;
381 	}
382 
383 	return false;
384 }
385 
386 /*
387  * software check exception is defined with risc-v cfi spec. Software check
388  * exception is raised when:
389  * a) An indirect branch doesn't land on 4 byte aligned PC or `lpad`
390  *    instruction or `label` value programmed in `lpad` instr doesn't
391  *    match with value setup in `x7`. reported code in `xtval` is 2.
392  * b) `sspopchk` instruction finds a mismatch between top of shadow stack (ssp)
393  *    and x1/x5. reported code in `xtval` is 3.
394  */
395 asmlinkage __visible __trap_section void do_trap_software_check(struct pt_regs *regs)
396 {
397 	if (user_mode(regs)) {
398 		irqentry_enter_from_user_mode(regs);
399 
400 		/* not a cfi violation, then merge into flow of unknown trap handler */
401 		if (!handle_user_cfi_violation(regs))
402 			do_trap_unknown(regs);
403 
404 		irqentry_exit_to_user_mode(regs);
405 	} else {
406 		/* sw check exception coming from kernel is a bug in kernel */
407 		die(regs, "Kernel BUG");
408 	}
409 }
410 
411 #ifdef CONFIG_MMU
412 asmlinkage __visible noinstr void do_page_fault(struct pt_regs *regs)
413 {
414 	irqentry_state_t state = irqentry_enter(regs);
415 
416 	handle_page_fault(regs);
417 
418 	local_irq_disable();
419 
420 	irqentry_exit(regs, state);
421 }
422 #endif
423 
424 static void noinstr handle_riscv_irq(struct pt_regs *regs)
425 {
426 	struct pt_regs *old_regs;
427 
428 	irq_enter_rcu();
429 	old_regs = set_irq_regs(regs);
430 	handle_arch_irq(regs);
431 	set_irq_regs(old_regs);
432 	irq_exit_rcu();
433 }
434 
435 asmlinkage void noinstr do_irq(struct pt_regs *regs)
436 {
437 	irqentry_state_t state = irqentry_enter(regs);
438 
439 	if (IS_ENABLED(CONFIG_IRQ_STACKS) && on_thread_stack())
440 		call_on_irq_stack(regs, handle_riscv_irq);
441 	else
442 		handle_riscv_irq(regs);
443 
444 	irqentry_exit(regs, state);
445 }
446 
447 #ifdef CONFIG_GENERIC_BUG
448 int is_valid_bugaddr(unsigned long pc)
449 {
450 	bug_insn_t insn;
451 
452 	if (pc < VMALLOC_START)
453 		return 0;
454 	if (get_kernel_nofault(insn, (bug_insn_t *)pc))
455 		return 0;
456 	if ((insn & __INSN_LENGTH_MASK) == __INSN_LENGTH_32)
457 		return (insn == __BUG_INSN_32);
458 	else
459 		return ((insn & __COMPRESSED_INSN_MASK) == __BUG_INSN_16);
460 }
461 #endif /* CONFIG_GENERIC_BUG */
462 
463 #ifdef CONFIG_VMAP_STACK
464 DEFINE_PER_CPU(unsigned long [OVERFLOW_STACK_SIZE/sizeof(long)],
465 		overflow_stack)__aligned(16);
466 
467 asmlinkage void handle_bad_stack(struct pt_regs *regs)
468 {
469 	unsigned long tsk_stk = (unsigned long)current->stack;
470 	unsigned long ovf_stk = (unsigned long)this_cpu_ptr(overflow_stack);
471 
472 	console_verbose();
473 
474 	pr_emerg("Insufficient stack space to handle exception!\n");
475 	pr_emerg("Task stack:     [0x%016lx..0x%016lx]\n",
476 			tsk_stk, tsk_stk + THREAD_SIZE);
477 	pr_emerg("Overflow stack: [0x%016lx..0x%016lx]\n",
478 			ovf_stk, ovf_stk + OVERFLOW_STACK_SIZE);
479 
480 	__show_regs(regs);
481 	panic("Kernel stack overflow");
482 
483 	for (;;)
484 		wait_for_interrupt();
485 }
486 #endif
487