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