1 // SPDX-License-Identifier: GPL-2.0-only
2 /*
3 * arch/arm/kernel/kprobes.c
4 *
5 * Kprobes on ARM
6 *
7 * Abhishek Sagar <sagar.abhishek@gmail.com>
8 * Copyright (C) 2006, 2007 Motorola Inc.
9 *
10 * Nicolas Pitre <nico@marvell.com>
11 * Copyright (C) 2007 Marvell Ltd.
12 */
13
14 #define pr_fmt(fmt) "kprobes: " fmt
15
16 #include <linux/kernel.h>
17 #include <linux/kprobes.h>
18 #include <linux/module.h>
19 #include <linux/slab.h>
20 #include <linux/stop_machine.h>
21 #include <linux/sched/debug.h>
22 #include <linux/stringify.h>
23 #include <asm/traps.h>
24 #include <asm/opcodes.h>
25 #include <asm/cacheflush.h>
26 #include <linux/percpu.h>
27 #include <linux/bug.h>
28 #include <asm/patch.h>
29 #include <asm/sections.h>
30
31 #include "../decode-arm.h"
32 #include "../decode-thumb.h"
33 #include "core.h"
34
35 #define MIN_STACK_SIZE(addr) \
36 min((unsigned long)MAX_STACK_SIZE, \
37 (unsigned long)current_thread_info() + THREAD_START_SP - (addr))
38
39 #define flush_insns(addr, size) \
40 flush_icache_range((unsigned long)(addr), \
41 (unsigned long)(addr) + \
42 (size))
43
44 DEFINE_PER_CPU(struct kprobe *, current_kprobe) = NULL;
45 DEFINE_PER_CPU(struct kprobe_ctlblk, kprobe_ctlblk);
46
47
48 int __kprobes arch_prepare_kprobe(struct kprobe *p)
49 {
50 kprobe_opcode_t insn;
51 kprobe_opcode_t tmp_insn[MAX_INSN_SIZE];
52 unsigned long addr = (unsigned long)p->addr;
53 bool thumb;
54 kprobe_decode_insn_t *decode_insn;
55 const union decode_action *actions;
56 int is;
57 const struct decode_checker **checkers;
58
59 #ifdef CONFIG_THUMB2_KERNEL
60 thumb = true;
61 addr &= ~1; /* Bit 0 would normally be set to indicate Thumb code */
62 insn = __mem_to_opcode_thumb16(((u16 *)addr)[0]);
63 if (is_wide_instruction(insn)) {
64 u16 inst2 = __mem_to_opcode_thumb16(((u16 *)addr)[1]);
65 insn = __opcode_thumb32_compose(insn, inst2);
66 decode_insn = thumb32_probes_decode_insn;
67 actions = kprobes_t32_actions;
68 checkers = kprobes_t32_checkers;
69 } else {
70 decode_insn = thumb16_probes_decode_insn;
71 actions = kprobes_t16_actions;
72 checkers = kprobes_t16_checkers;
73 }
74 #else /* !CONFIG_THUMB2_KERNEL */
75 thumb = false;
76 if (addr & 0x3)
77 return -EINVAL;
78 insn = __mem_to_opcode_arm(*p->addr);
79 decode_insn = arm_probes_decode_insn;
80 actions = kprobes_arm_actions;
81 checkers = kprobes_arm_checkers;
82 #endif
83
84 p->opcode = insn;
85 p->ainsn.insn = tmp_insn;
86
87 switch ((*decode_insn)(insn, &p->ainsn, true, actions, checkers)) {
88 case INSN_REJECTED: /* not supported */
89 return -EINVAL;
90
91 case INSN_GOOD: /* instruction uses slot */
92 p->ainsn.insn = get_insn_slot();
93 if (!p->ainsn.insn)
94 return -ENOMEM;
95 for (is = 0; is < MAX_INSN_SIZE; ++is)
96 p->ainsn.insn[is] = tmp_insn[is];
97 flush_insns(p->ainsn.insn,
98 sizeof(p->ainsn.insn[0]) * MAX_INSN_SIZE);
99 p->ainsn.insn_fn = (probes_insn_fn_t *)
100 ((uintptr_t)p->ainsn.insn | thumb);
101 break;
102
103 case INSN_GOOD_NO_SLOT: /* instruction doesn't need insn slot */
104 p->ainsn.insn = NULL;
105 break;
106 }
107
108 /*
109 * Never instrument insn like 'str r0, [sp, +/-r1]'. Also, insn likes
110 * 'str r0, [sp, #-68]' should also be prohibited.
111 * See __und_svc.
112 */
113 if ((p->ainsn.stack_space < 0) ||
114 (p->ainsn.stack_space > MAX_STACK_SIZE))
115 return -EINVAL;
116
117 return 0;
118 }
119
120 void __kprobes arch_arm_kprobe(struct kprobe *p)
121 {
122 unsigned int brkp;
123 void *addr;
124
125 if (IS_ENABLED(CONFIG_THUMB2_KERNEL)) {
126 /* Remove any Thumb flag */
127 addr = (void *)((uintptr_t)p->addr & ~1);
128
129 if (is_wide_instruction(p->opcode))
130 brkp = KPROBE_THUMB32_BREAKPOINT_INSTRUCTION;
131 else
132 brkp = KPROBE_THUMB16_BREAKPOINT_INSTRUCTION;
133 } else {
134 kprobe_opcode_t insn = p->opcode;
135
136 addr = p->addr;
137 brkp = KPROBE_ARM_BREAKPOINT_INSTRUCTION;
138
139 if (insn >= 0xe0000000)
140 brkp |= 0xe0000000; /* Unconditional instruction */
141 else
142 brkp |= insn & 0xf0000000; /* Copy condition from insn */
143 }
144
145 patch_text(addr, brkp);
146 }
147
148 /*
149 * The actual disarming is done here on each CPU and synchronized using
150 * stop_machine. This synchronization is necessary on SMP to avoid removing
151 * a probe between the moment the 'Undefined Instruction' exception is raised
152 * and the moment the exception handler reads the faulting instruction from
153 * memory. It is also needed to atomically set the two half-words of a 32-bit
154 * Thumb breakpoint.
155 */
156 struct patch {
157 void *addr;
158 unsigned int insn;
159 };
160
161 static int __kprobes_remove_breakpoint(void *data)
162 {
163 struct patch *p = data;
164 __patch_text(p->addr, p->insn);
165 return 0;
166 }
167
168 void __kprobes kprobes_remove_breakpoint(void *addr, unsigned int insn)
169 {
170 struct patch p = {
171 .addr = addr,
172 .insn = insn,
173 };
174 stop_machine_cpuslocked(__kprobes_remove_breakpoint, &p,
175 cpu_online_mask);
176 }
177
178 void __kprobes arch_disarm_kprobe(struct kprobe *p)
179 {
180 kprobes_remove_breakpoint((void *)((uintptr_t)p->addr & ~1),
181 p->opcode);
182 }
183
184 void __kprobes arch_remove_kprobe(struct kprobe *p)
185 {
186 if (p->ainsn.insn) {
187 free_insn_slot(p->ainsn.insn, 0);
188 p->ainsn.insn = NULL;
189 }
190 }
191
192 static void __kprobes save_previous_kprobe(struct kprobe_ctlblk *kcb)
193 {
194 kcb->prev_kprobe.kp = kprobe_running();
195 kcb->prev_kprobe.status = kcb->kprobe_status;
196 }
197
198 static void __kprobes restore_previous_kprobe(struct kprobe_ctlblk *kcb)
199 {
200 __this_cpu_write(current_kprobe, kcb->prev_kprobe.kp);
201 kcb->kprobe_status = kcb->prev_kprobe.status;
202 }
203
204 static void __kprobes set_current_kprobe(struct kprobe *p)
205 {
206 __this_cpu_write(current_kprobe, p);
207 }
208
209 static void __kprobes
210 singlestep_skip(struct kprobe *p, struct pt_regs *regs)
211 {
212 #ifdef CONFIG_THUMB2_KERNEL
213 regs->ARM_cpsr = it_advance(regs->ARM_cpsr);
214 if (is_wide_instruction(p->opcode))
215 regs->ARM_pc += 4;
216 else
217 regs->ARM_pc += 2;
218 #else
219 regs->ARM_pc += 4;
220 #endif
221 }
222
223 static inline void __kprobes
224 singlestep(struct kprobe *p, struct pt_regs *regs, struct kprobe_ctlblk *kcb)
225 {
226 p->ainsn.insn_singlestep(p->opcode, &p->ainsn, regs);
227 }
228
229 /*
230 * Called with IRQs disabled. IRQs must remain disabled from that point
231 * all the way until processing this kprobe is complete. The current
232 * kprobes implementation cannot process more than one nested level of
233 * kprobe, and that level is reserved for user kprobe handlers, so we can't
234 * risk encountering a new kprobe in an interrupt handler.
235 */
236 static void __kprobes kprobe_handler(struct pt_regs *regs)
237 {
238 struct kprobe *p, *cur;
239 struct kprobe_ctlblk *kcb;
240
241 kcb = get_kprobe_ctlblk();
242 cur = kprobe_running();
243
244 #ifdef CONFIG_THUMB2_KERNEL
245 /*
246 * First look for a probe which was registered using an address with
247 * bit 0 set, this is the usual situation for pointers to Thumb code.
248 * If not found, fallback to looking for one with bit 0 clear.
249 */
250 p = get_kprobe((kprobe_opcode_t *)(regs->ARM_pc | 1));
251 if (!p)
252 p = get_kprobe((kprobe_opcode_t *)regs->ARM_pc);
253
254 #else /* ! CONFIG_THUMB2_KERNEL */
255 p = get_kprobe((kprobe_opcode_t *)regs->ARM_pc);
256 #endif
257
258 if (p) {
259 if (!p->ainsn.insn_check_cc(regs->ARM_cpsr)) {
260 /*
261 * Probe hit but conditional execution check failed,
262 * so just skip the instruction and continue as if
263 * nothing had happened.
264 * In this case, we can skip recursing check too.
265 */
266 singlestep_skip(p, regs);
267 } else if (cur) {
268 /* Kprobe is pending, so we're recursing. */
269 switch (kcb->kprobe_status) {
270 case KPROBE_HIT_ACTIVE:
271 case KPROBE_HIT_SSDONE:
272 case KPROBE_HIT_SS:
273 /* A pre- or post-handler probe got us here. */
274 kprobes_inc_nmissed_count(p);
275 save_previous_kprobe(kcb);
276 set_current_kprobe(p);
277 kcb->kprobe_status = KPROBE_REENTER;
278 singlestep(p, regs, kcb);
279 restore_previous_kprobe(kcb);
280 break;
281 case KPROBE_REENTER:
282 /* A nested probe was hit in FIQ, it is a BUG */
283 pr_warn("Failed to recover from reentered kprobes.\n");
284 dump_kprobe(p);
285 fallthrough;
286 default:
287 /* impossible cases */
288 BUG();
289 }
290 } else {
291 /* Probe hit and conditional execution check ok. */
292 set_current_kprobe(p);
293 kcb->kprobe_status = KPROBE_HIT_ACTIVE;
294
295 /*
296 * If we have no pre-handler or it returned 0, we
297 * continue with normal processing. If we have a
298 * pre-handler and it returned non-zero, it will
299 * modify the execution path and no need to single
300 * stepping. Let's just reset current kprobe and exit.
301 */
302 if (!p->pre_handler || !p->pre_handler(p, regs)) {
303 kcb->kprobe_status = KPROBE_HIT_SS;
304 singlestep(p, regs, kcb);
305 if (p->post_handler) {
306 kcb->kprobe_status = KPROBE_HIT_SSDONE;
307 p->post_handler(p, regs, 0);
308 }
309 }
310 reset_current_kprobe();
311 }
312 } else {
313 /*
314 * The probe was removed and a race is in progress.
315 * There is nothing we can do about it. Let's restart
316 * the instruction. By the time we can restart, the
317 * real instruction will be there.
318 */
319 }
320 }
321
322 static int __kprobes kprobe_trap_handler(struct pt_regs *regs, unsigned int instr)
323 {
324 unsigned long flags;
325 local_irq_save(flags);
326 kprobe_handler(regs);
327 local_irq_restore(flags);
328 return 0;
329 }
330
331 int __kprobes kprobe_fault_handler(struct pt_regs *regs, unsigned int fsr)
332 {
333 struct kprobe *cur = kprobe_running();
334 struct kprobe_ctlblk *kcb = get_kprobe_ctlblk();
335
336 switch (kcb->kprobe_status) {
337 case KPROBE_HIT_SS:
338 case KPROBE_REENTER:
339 /*
340 * We are here because the instruction being single
341 * stepped caused a page fault. We reset the current
342 * kprobe and the PC to point back to the probe address
343 * and allow the page fault handler to continue as a
344 * normal page fault.
345 */
346 regs->ARM_pc = (long)cur->addr;
347 if (kcb->kprobe_status == KPROBE_REENTER) {
348 restore_previous_kprobe(kcb);
349 } else {
350 reset_current_kprobe();
351 }
352 break;
353 }
354
355 return 0;
356 }
357
358 int __kprobes kprobe_exceptions_notify(struct notifier_block *self,
359 unsigned long val, void *data)
360 {
361 /*
362 * notify_die() is currently never called on ARM,
363 * so this callback is currently empty.
364 */
365 return NOTIFY_DONE;
366 }
367
368 /*
369 * When a retprobed function returns, trampoline_handler() is called,
370 * calling the kretprobe's handler. We construct a struct pt_regs to
371 * give a view of registers r0-r11, sp, lr, and pc to the user
372 * return-handler. This is not a complete pt_regs structure, but that
373 * should be enough for stacktrace from the return handler with or
374 * without pt_regs.
375 */
376 void __naked __kprobes __kretprobe_trampoline(void)
377 {
378 __asm__ __volatile__ (
379 #ifdef CONFIG_FRAME_POINTER
380 "ldr lr, =__kretprobe_trampoline \n\t"
381 /* __kretprobe_trampoline makes a framepointer on pt_regs. */
382 #ifdef CONFIG_CC_IS_CLANG
383 "stmdb sp, {sp, lr, pc} \n\t"
384 "sub sp, sp, #12 \n\t"
385 /* In clang case, pt_regs->ip = lr. */
386 "stmdb sp!, {r0 - r11, lr} \n\t"
387 /* fp points regs->r11 (fp) */
388 "add fp, sp, #44 \n\t"
389 #else /* !CONFIG_CC_IS_CLANG */
390 /* In gcc case, pt_regs->ip = fp. */
391 "stmdb sp, {fp, sp, lr, pc} \n\t"
392 "sub sp, sp, #16 \n\t"
393 "stmdb sp!, {r0 - r11} \n\t"
394 /* fp points regs->r15 (pc) */
395 "add fp, sp, #60 \n\t"
396 #endif /* CONFIG_CC_IS_CLANG */
397 #else /* !CONFIG_FRAME_POINTER */
398 "sub sp, sp, #16 \n\t"
399 "stmdb sp!, {r0 - r11} \n\t"
400 #endif /* CONFIG_FRAME_POINTER */
401 "mov r0, sp \n\t"
402 "bl trampoline_handler \n\t"
403 "mov lr, r0 \n\t"
404 "ldmia sp!, {r0 - r11} \n\t"
405 "add sp, sp, #16 \n\t"
406 #ifdef CONFIG_THUMB2_KERNEL
407 "bx lr \n\t"
408 #else
409 "mov pc, lr \n\t"
410 #endif
411 : : : "memory");
412 }
413
414 /* Called from __kretprobe_trampoline */
415 static __used __kprobes void *trampoline_handler(struct pt_regs *regs)
416 {
417 return (void *)kretprobe_trampoline_handler(regs, (void *)regs->ARM_fp);
418 }
419
420 void __kprobes arch_prepare_kretprobe(struct kretprobe_instance *ri,
421 struct pt_regs *regs)
422 {
423 ri->ret_addr = (kprobe_opcode_t *)regs->ARM_lr;
424 ri->fp = (void *)regs->ARM_fp;
425
426 /* Replace the return addr with trampoline addr. */
427 regs->ARM_lr = (unsigned long)&__kretprobe_trampoline;
428 }
429
430 int __kprobes arch_trampoline_kprobe(struct kprobe *p)
431 {
432 return 0;
433 }
434
435 #ifdef CONFIG_THUMB2_KERNEL
436
437 static struct undef_hook kprobes_thumb16_break_hook = {
438 .instr_mask = 0xffff,
439 .instr_val = KPROBE_THUMB16_BREAKPOINT_INSTRUCTION,
440 .cpsr_mask = MODE_MASK,
441 .cpsr_val = SVC_MODE,
442 .fn = kprobe_trap_handler,
443 };
444
445 static struct undef_hook kprobes_thumb32_break_hook = {
446 .instr_mask = 0xffffffff,
447 .instr_val = KPROBE_THUMB32_BREAKPOINT_INSTRUCTION,
448 .cpsr_mask = MODE_MASK,
449 .cpsr_val = SVC_MODE,
450 .fn = kprobe_trap_handler,
451 };
452
453 #else /* !CONFIG_THUMB2_KERNEL */
454
455 static struct undef_hook kprobes_arm_break_hook = {
456 .instr_mask = 0x0fffffff,
457 .instr_val = KPROBE_ARM_BREAKPOINT_INSTRUCTION,
458 .cpsr_mask = MODE_MASK,
459 .cpsr_val = SVC_MODE,
460 .fn = kprobe_trap_handler,
461 };
462
463 #endif /* !CONFIG_THUMB2_KERNEL */
464
465 int __init arch_init_kprobes(void)
466 {
467 arm_probes_decode_init();
468 #ifdef CONFIG_THUMB2_KERNEL
469 register_undef_hook(&kprobes_thumb16_break_hook);
470 register_undef_hook(&kprobes_thumb32_break_hook);
471 #else
472 register_undef_hook(&kprobes_arm_break_hook);
473 #endif
474 return 0;
475 }
476
477 bool arch_within_kprobe_blacklist(unsigned long addr)
478 {
479 void *a = (void *)addr;
480
481 return __in_irqentry_text(addr) ||
482 in_entry_text(addr) ||
483 in_idmap_text(addr) ||
484 memory_contains(__kprobes_text_start, __kprobes_text_end, a, 1);
485 }
486
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