1 // SPDX-License-Identifier: GPL-2.0-or-later
2 /*
3 * Kernel Probes Jump Optimization (Optprobes)
4 *
5 * Copyright (C) IBM Corporation, 2002, 2004
6 * Copyright (C) Hitachi Ltd., 2012
7 */
8 #include <linux/kprobes.h>
9 #include <linux/perf_event.h>
10 #include <linux/ptrace.h>
11 #include <linux/string.h>
12 #include <linux/slab.h>
13 #include <linux/hardirq.h>
14 #include <linux/preempt.h>
15 #include <linux/extable.h>
16 #include <linux/kdebug.h>
17 #include <linux/kallsyms.h>
18 #include <linux/kgdb.h>
19 #include <linux/ftrace.h>
20 #include <linux/objtool.h>
21 #include <linux/pgtable.h>
22 #include <linux/static_call.h>
23
24 #include <asm/text-patching.h>
25 #include <asm/cacheflush.h>
26 #include <asm/desc.h>
27 #include <linux/uaccess.h>
28 #include <asm/alternative.h>
29 #include <asm/insn.h>
30 #include <asm/debugreg.h>
31 #include <asm/set_memory.h>
32 #include <asm/sections.h>
33 #include <asm/nospec-branch.h>
34
35 #include "common.h"
36
37 unsigned long __recover_optprobed_insn(kprobe_opcode_t *buf, unsigned long addr)
38 {
39 struct optimized_kprobe *op;
40 struct kprobe *kp;
41 long offs;
42 int i;
43
44 for (i = 0; i < JMP32_INSN_SIZE; i++) {
45 kp = get_kprobe((void *)addr - i);
46 /* This function only handles jump-optimized kprobe */
47 if (kp && kprobe_optimized(kp)) {
48 op = container_of(kp, struct optimized_kprobe, kp);
49 /* If op is optimized or under unoptimizing */
50 if (list_empty(&op->list) || optprobe_queued_unopt(op))
51 goto found;
52 }
53 }
54
55 return addr;
56 found:
57 /*
58 * If the kprobe can be optimized, original bytes which can be
59 * overwritten by jump destination address. In this case, original
60 * bytes must be recovered from op->optinsn.copied_insn buffer.
61 */
62 if (copy_from_kernel_nofault(buf, (void *)addr,
63 MAX_INSN_SIZE * sizeof(kprobe_opcode_t)))
64 return 0UL;
65
66 if (addr == (unsigned long)kp->addr) {
67 buf[0] = kp->opcode;
68 memcpy(buf + 1, op->optinsn.copied_insn, DISP32_SIZE);
69 } else {
70 offs = addr - (unsigned long)kp->addr - 1;
71 memcpy(buf, op->optinsn.copied_insn + offs, DISP32_SIZE - offs);
72 }
73
74 return (unsigned long)buf;
75 }
76
77 static void synthesize_clac(kprobe_opcode_t *addr)
78 {
79 /*
80 * Can't be static_cpu_has() due to how objtool treats this feature bit.
81 * This isn't a fast path anyway.
82 */
83 if (!boot_cpu_has(X86_FEATURE_SMAP))
84 return;
85
86 /* Replace the NOP3 with CLAC */
87 addr[0] = 0x0f;
88 addr[1] = 0x01;
89 addr[2] = 0xca;
90 }
91
92 /* Insert a move instruction which sets a pointer to eax/rdi (1st arg). */
93 static void synthesize_set_arg1(kprobe_opcode_t *addr, unsigned long val)
94 {
95 #ifdef CONFIG_X86_64
96 *addr++ = 0x48;
97 *addr++ = 0xbf;
98 #else
99 *addr++ = 0xb8;
100 #endif
101 *(unsigned long *)addr = val;
102 }
103
104 asm (
105 ".pushsection .rodata\n"
106 "optprobe_template_func:\n"
107 ".global optprobe_template_entry\n"
108 "optprobe_template_entry:\n"
109 #ifdef CONFIG_X86_64
110 " pushq $" __stringify(__KERNEL_DS) "\n"
111 /* Save the 'sp - 8', this will be fixed later. */
112 " pushq %rsp\n"
113 " pushfq\n"
114 ".global optprobe_template_clac\n"
115 "optprobe_template_clac:\n"
116 ASM_NOP3
117 SAVE_REGS_STRING
118 " movq %rsp, %rsi\n"
119 ".global optprobe_template_val\n"
120 "optprobe_template_val:\n"
121 ASM_NOP5
122 ASM_NOP5
123 ".global optprobe_template_call\n"
124 "optprobe_template_call:\n"
125 ASM_NOP5
126 /* Copy 'regs->flags' into 'regs->ss'. */
127 " movq 18*8(%rsp), %rdx\n"
128 " movq %rdx, 20*8(%rsp)\n"
129 RESTORE_REGS_STRING
130 /* Skip 'regs->flags' and 'regs->sp'. */
131 " addq $16, %rsp\n"
132 /* And pop flags register from 'regs->ss'. */
133 " popfq\n"
134 #else /* CONFIG_X86_32 */
135 " pushl %ss\n"
136 /* Save the 'sp - 4', this will be fixed later. */
137 " pushl %esp\n"
138 " pushfl\n"
139 ".global optprobe_template_clac\n"
140 "optprobe_template_clac:\n"
141 ASM_NOP3
142 SAVE_REGS_STRING
143 " movl %esp, %edx\n"
144 ".global optprobe_template_val\n"
145 "optprobe_template_val:\n"
146 ASM_NOP5
147 ".global optprobe_template_call\n"
148 "optprobe_template_call:\n"
149 ASM_NOP5
150 /* Copy 'regs->flags' into 'regs->ss'. */
151 " movl 14*4(%esp), %edx\n"
152 " movl %edx, 16*4(%esp)\n"
153 RESTORE_REGS_STRING
154 /* Skip 'regs->flags' and 'regs->sp'. */
155 " addl $8, %esp\n"
156 /* And pop flags register from 'regs->ss'. */
157 " popfl\n"
158 #endif
159 ".global optprobe_template_end\n"
160 "optprobe_template_end:\n"
161 ".popsection\n");
162
163 void optprobe_template_func(void);
164 STACK_FRAME_NON_STANDARD(optprobe_template_func);
165
166 #define TMPL_CLAC_IDX \
167 ((long)optprobe_template_clac - (long)optprobe_template_entry)
168 #define TMPL_MOVE_IDX \
169 ((long)optprobe_template_val - (long)optprobe_template_entry)
170 #define TMPL_CALL_IDX \
171 ((long)optprobe_template_call - (long)optprobe_template_entry)
172 #define TMPL_END_IDX \
173 ((long)optprobe_template_end - (long)optprobe_template_entry)
174
175 /* Optimized kprobe call back function: called from optinsn */
176 static void
177 optimized_callback(struct optimized_kprobe *op, struct pt_regs *regs)
178 {
179 /* This is possible if op is under delayed unoptimizing */
180 if (kprobe_disabled(&op->kp))
181 return;
182
183 preempt_disable();
184 if (kprobe_running()) {
185 kprobes_inc_nmissed_count(&op->kp);
186 } else {
187 struct kprobe_ctlblk *kcb = get_kprobe_ctlblk();
188 /* Adjust stack pointer */
189 regs->sp += sizeof(long);
190 /* Save skipped registers */
191 regs->cs = __KERNEL_CS;
192 #ifdef CONFIG_X86_32
193 regs->gs = 0;
194 #endif
195 regs->ip = (unsigned long)op->kp.addr + INT3_INSN_SIZE;
196 regs->orig_ax = ~0UL;
197
198 __this_cpu_write(current_kprobe, &op->kp);
199 kcb->kprobe_status = KPROBE_HIT_ACTIVE;
200 opt_pre_handler(&op->kp, regs);
201 __this_cpu_write(current_kprobe, NULL);
202 }
203 preempt_enable();
204 }
205 NOKPROBE_SYMBOL(optimized_callback);
206
207 static int copy_optimized_instructions(u8 *dest, u8 *src, u8 *real)
208 {
209 struct insn insn;
210 int len = 0, ret;
211
212 while (len < JMP32_INSN_SIZE) {
213 ret = __copy_instruction(dest + len, src + len, real + len, &insn);
214 if (!ret || !can_boost(&insn, src + len))
215 return -EINVAL;
216 len += ret;
217 }
218 /* Check whether the address range is reserved */
219 if (ftrace_text_reserved(src, src + len - 1) ||
220 alternatives_text_reserved(src, src + len - 1) ||
221 jump_label_text_reserved(src, src + len - 1) ||
222 static_call_text_reserved(src, src + len - 1))
223 return -EBUSY;
224
225 return len;
226 }
227
228 /* Check whether insn is indirect jump */
229 static int insn_is_indirect_jump(struct insn *insn)
230 {
231 return ((insn->opcode.bytes[0] == 0xff &&
232 (X86_MODRM_REG(insn->modrm.value) & 6) == 4) || /* Jump */
233 insn->opcode.bytes[0] == 0xea); /* Segment based jump */
234 }
235
236 /* Check whether insn jumps into specified address range */
237 static int insn_jump_into_range(struct insn *insn, unsigned long start, int len)
238 {
239 unsigned long target = 0;
240
241 switch (insn->opcode.bytes[0]) {
242 case 0xe0: /* loopne */
243 case 0xe1: /* loope */
244 case 0xe2: /* loop */
245 case 0xe3: /* jcxz */
246 case 0xe9: /* near relative jump */
247 case 0xeb: /* short relative jump */
248 break;
249 case 0x0f:
250 if ((insn->opcode.bytes[1] & 0xf0) == 0x80) /* jcc near */
251 break;
252 return 0;
253 default:
254 if ((insn->opcode.bytes[0] & 0xf0) == 0x70) /* jcc short */
255 break;
256 return 0;
257 }
258 target = (unsigned long)insn->next_byte + insn->immediate.value;
259
260 return (start <= target && target <= start + len);
261 }
262
263 /* Decode whole function to ensure any instructions don't jump into target */
264 static int can_optimize(unsigned long paddr)
265 {
266 unsigned long addr, size = 0, offset = 0;
267 struct insn insn;
268 kprobe_opcode_t buf[MAX_INSN_SIZE];
269
270 /* Lookup symbol including addr */
271 if (!kallsyms_lookup_size_offset(paddr, &size, &offset))
272 return 0;
273
274 /*
275 * Do not optimize in the entry code due to the unstable
276 * stack handling and registers setup.
277 */
278 if (((paddr >= (unsigned long)__entry_text_start) &&
279 (paddr < (unsigned long)__entry_text_end)))
280 return 0;
281
282 /* Check there is enough space for a relative jump. */
283 if (size - offset < JMP32_INSN_SIZE)
284 return 0;
285
286 /* Decode instructions */
287 addr = paddr - offset;
288 while (addr < paddr - offset + size) { /* Decode until function end */
289 unsigned long recovered_insn;
290 int ret;
291
292 if (search_exception_tables(addr))
293 /*
294 * Since some fixup code will jumps into this function,
295 * we can't optimize kprobe in this function.
296 */
297 return 0;
298 recovered_insn = recover_probed_instruction(buf, addr);
299 if (!recovered_insn)
300 return 0;
301
302 ret = insn_decode_kernel(&insn, (void *)recovered_insn);
303 if (ret < 0)
304 return 0;
305 #ifdef CONFIG_KGDB
306 /*
307 * If there is a dynamically installed kgdb sw breakpoint,
308 * this function should not be probed.
309 */
310 if (insn.opcode.bytes[0] == INT3_INSN_OPCODE &&
311 kgdb_has_hit_break(addr))
312 return 0;
313 #endif
314 /* Recover address */
315 insn.kaddr = (void *)addr;
316 insn.next_byte = (void *)(addr + insn.length);
317 /*
318 * Check any instructions don't jump into target, indirectly or
319 * directly.
320 *
321 * The indirect case is present to handle a code with jump
322 * tables. When the kernel uses retpolines, the check should in
323 * theory additionally look for jumps to indirect thunks.
324 * However, the kernel built with retpolines or IBT has jump
325 * tables disabled so the check can be skipped altogether.
326 */
327 if (!IS_ENABLED(CONFIG_MITIGATION_RETPOLINE) &&
328 !IS_ENABLED(CONFIG_X86_KERNEL_IBT) &&
329 insn_is_indirect_jump(&insn))
330 return 0;
331 if (insn_jump_into_range(&insn, paddr + INT3_INSN_SIZE,
332 DISP32_SIZE))
333 return 0;
334 addr += insn.length;
335 }
336
337 return 1;
338 }
339
340 /* Check optimized_kprobe can actually be optimized. */
341 int arch_check_optimized_kprobe(struct optimized_kprobe *op)
342 {
343 int i;
344 struct kprobe *p;
345
346 for (i = 1; i < op->optinsn.size; i++) {
347 p = get_kprobe(op->kp.addr + i);
348 if (p && !kprobe_disarmed(p))
349 return -EEXIST;
350 }
351
352 return 0;
353 }
354
355 /* Check the addr is within the optimized instructions. */
356 int arch_within_optimized_kprobe(struct optimized_kprobe *op,
357 kprobe_opcode_t *addr)
358 {
359 return (op->kp.addr <= addr &&
360 op->kp.addr + op->optinsn.size > addr);
361 }
362
363 /* Free optimized instruction slot */
364 static
365 void __arch_remove_optimized_kprobe(struct optimized_kprobe *op, int dirty)
366 {
367 u8 *slot = op->optinsn.insn;
368 if (slot) {
369 int len = TMPL_END_IDX + op->optinsn.size + JMP32_INSN_SIZE;
370
371 /* Record the perf event before freeing the slot */
372 if (dirty)
373 perf_event_text_poke(slot, slot, len, NULL, 0);
374
375 free_optinsn_slot(slot, dirty);
376 op->optinsn.insn = NULL;
377 op->optinsn.size = 0;
378 }
379 }
380
381 void arch_remove_optimized_kprobe(struct optimized_kprobe *op)
382 {
383 __arch_remove_optimized_kprobe(op, 1);
384 }
385
386 /*
387 * Copy replacing target instructions
388 * Target instructions MUST be relocatable (checked inside)
389 * This is called when new aggr(opt)probe is allocated or reused.
390 */
391 int arch_prepare_optimized_kprobe(struct optimized_kprobe *op,
392 struct kprobe *__unused)
393 {
394 u8 *buf = NULL, *slot;
395 int ret, len;
396 long rel;
397
398 if (!can_optimize((unsigned long)op->kp.addr))
399 return -EILSEQ;
400
401 buf = kzalloc(MAX_OPTINSN_SIZE, GFP_KERNEL);
402 if (!buf)
403 return -ENOMEM;
404
405 op->optinsn.insn = slot = get_optinsn_slot();
406 if (!slot) {
407 ret = -ENOMEM;
408 goto out;
409 }
410
411 /*
412 * Verify if the address gap is in 2GB range, because this uses
413 * a relative jump.
414 */
415 rel = (long)slot - (long)op->kp.addr + JMP32_INSN_SIZE;
416 if (abs(rel) > 0x7fffffff) {
417 ret = -ERANGE;
418 goto err;
419 }
420
421 /* Copy arch-dep-instance from template */
422 memcpy(buf, optprobe_template_entry, TMPL_END_IDX);
423
424 /* Copy instructions into the out-of-line buffer */
425 ret = copy_optimized_instructions(buf + TMPL_END_IDX, op->kp.addr,
426 slot + TMPL_END_IDX);
427 if (ret < 0)
428 goto err;
429 op->optinsn.size = ret;
430 len = TMPL_END_IDX + op->optinsn.size;
431
432 synthesize_clac(buf + TMPL_CLAC_IDX);
433
434 /* Set probe information */
435 synthesize_set_arg1(buf + TMPL_MOVE_IDX, (unsigned long)op);
436
437 /* Set probe function call */
438 synthesize_relcall(buf + TMPL_CALL_IDX,
439 slot + TMPL_CALL_IDX, optimized_callback);
440
441 /* Set returning jmp instruction at the tail of out-of-line buffer */
442 synthesize_reljump(buf + len, slot + len,
443 (u8 *)op->kp.addr + op->optinsn.size);
444 len += JMP32_INSN_SIZE;
445
446 /*
447 * Note len = TMPL_END_IDX + op->optinsn.size + JMP32_INSN_SIZE is also
448 * used in __arch_remove_optimized_kprobe().
449 */
450
451 /* We have to use text_poke() for instruction buffer because it is RO */
452 perf_event_text_poke(slot, NULL, 0, buf, len);
453 text_poke(slot, buf, len);
454
455 ret = 0;
456 out:
457 kfree(buf);
458 return ret;
459
460 err:
461 __arch_remove_optimized_kprobe(op, 0);
462 goto out;
463 }
464
465 /*
466 * Replace breakpoints (INT3) with relative jumps (JMP.d32).
467 * Caller must call with locking kprobe_mutex and text_mutex.
468 *
469 * The caller will have installed a regular kprobe and after that issued
470 * syncrhonize_rcu_tasks(), this ensures that the instruction(s) that live in
471 * the 4 bytes after the INT3 are unused and can now be overwritten.
472 */
473 void arch_optimize_kprobes(struct list_head *oplist)
474 {
475 struct optimized_kprobe *op, *tmp;
476 u8 insn_buff[JMP32_INSN_SIZE];
477
478 list_for_each_entry_safe(op, tmp, oplist, list) {
479 s32 rel = (s32)((long)op->optinsn.insn -
480 ((long)op->kp.addr + JMP32_INSN_SIZE));
481
482 WARN_ON(kprobe_disabled(&op->kp));
483
484 /* Backup instructions which will be replaced by jump address */
485 memcpy(op->optinsn.copied_insn, op->kp.addr + INT3_INSN_SIZE,
486 DISP32_SIZE);
487
488 insn_buff[0] = JMP32_INSN_OPCODE;
489 *(s32 *)(&insn_buff[1]) = rel;
490
491 text_poke_bp(op->kp.addr, insn_buff, JMP32_INSN_SIZE, NULL);
492
493 list_del_init(&op->list);
494 }
495 }
496
497 /*
498 * Replace a relative jump (JMP.d32) with a breakpoint (INT3).
499 *
500 * After that, we can restore the 4 bytes after the INT3 to undo what
501 * arch_optimize_kprobes() scribbled. This is safe since those bytes will be
502 * unused once the INT3 lands.
503 */
504 void arch_unoptimize_kprobe(struct optimized_kprobe *op)
505 {
506 u8 new[JMP32_INSN_SIZE] = { INT3_INSN_OPCODE, };
507 u8 old[JMP32_INSN_SIZE];
508 u8 *addr = op->kp.addr;
509
510 memcpy(old, op->kp.addr, JMP32_INSN_SIZE);
511 memcpy(new + INT3_INSN_SIZE,
512 op->optinsn.copied_insn,
513 JMP32_INSN_SIZE - INT3_INSN_SIZE);
514
515 text_poke(addr, new, INT3_INSN_SIZE);
516 text_poke_sync();
517 text_poke(addr + INT3_INSN_SIZE,
518 new + INT3_INSN_SIZE,
519 JMP32_INSN_SIZE - INT3_INSN_SIZE);
520 text_poke_sync();
521
522 perf_event_text_poke(op->kp.addr, old, JMP32_INSN_SIZE, new, JMP32_INSN_SIZE);
523 }
524
525 /*
526 * Recover original instructions and breakpoints from relative jumps.
527 * Caller must call with locking kprobe_mutex.
528 */
529 extern void arch_unoptimize_kprobes(struct list_head *oplist,
530 struct list_head *done_list)
531 {
532 struct optimized_kprobe *op, *tmp;
533
534 list_for_each_entry_safe(op, tmp, oplist, list) {
535 arch_unoptimize_kprobe(op);
536 list_move(&op->list, done_list);
537 }
538 }
539
540 int setup_detour_execution(struct kprobe *p, struct pt_regs *regs, int reenter)
541 {
542 struct optimized_kprobe *op;
543
544 if (p->flags & KPROBE_FLAG_OPTIMIZED) {
545 /* This kprobe is really able to run optimized path. */
546 op = container_of(p, struct optimized_kprobe, kp);
547 /* Detour through copied instructions */
548 regs->ip = (unsigned long)op->optinsn.insn + TMPL_END_IDX;
549 if (!reenter)
550 reset_current_kprobe();
551 return 1;
552 }
553 return 0;
554 }
555 NOKPROBE_SYMBOL(setup_detour_execution);
556
Linux® is a registered trademark of Linus Torvalds in the United States and other countries.
TOMOYO® is a registered trademark of NTT DATA CORPORATION.