1
2
3
4
5
6
7
8
9
10
11
12
13
14
15
16
17
18
19
20
21
22
23
24
25
26
27
28
29
30
31
32
33
34
35
36
37
38
39
40
41
42
43
44
45
46
47
48
49
50
51
52
53
54
55
56
57
58
59
60
61
62
63
64
65
66
67
68
69
70
71
72
73
74
75
76
77
78
79
80
81
82
83
84
85
86
87
88
89
90
91
92
93
94
95
96
97
98
99
100
101
102
103
104
105
106
107
108
109
110
111
112
113
114
115
116
117
118
119
120
121
122
123
124
125
126
127
128
129
130
131
132
133
134
135
136
137
138
139
140
141
142
143
144
145
146
147
148
149
150
151
152
153
154
155
156
157
158
159
160
161
162
163
164
165
166
167
168
169
170
171
172
173
174
175
176
177
178
179
180
181
182
183
184
185
186
187
188
189
190
191
192
193
194
195
196
197
198
199
200
201
202
203
204
205
206
207
208
209
210
211
212
213
214
215
216
217
218
219
220
221
222
223
224
225
226
227
228
229
230
231
232
233
234
235
236
237
238
239
240
241
242
243
244
245
246
247
248
249
250
251
252
253
254
255
256
257
258
259
260
261
262
263
264
265
266
267
268
269
270
271
272
273
274
275
276
277
278
279
280
281
282
283
284
285
286
287
288
289
290
291
292
293
294
295
296
297
298
299
300
301
302
303
304
305
306
307
308
309
310
311
312
313
314
315
316
317
318
319
320
321
322
323
324
325
326
327
328
329
330
331
332
333
334
335
336
337
338
339
340
341
342
343
344
345
346
347
348
349
350
351
352
353
354
355
356
357
358
359
360
361
362
363
364
365
366
367
368
369
370
371
372
373
374
375
376
377
378
379
380
381
382
383
384
385
386
387
388
389
390
391
392
393
394
395
396
397
398
399
400
401
402
403
404
405
406
407
408
409
410
411
412
413
414
415
416
417
418
419
420
421
422
423
424
425
426
427
428
429
430
431
432
433
434
435
436
437
438
439
440
441
442
443
444
445
446
447
448
449
450
451
452
453
454
455
456
457
458
459
460
461
462
463
464
465
466
467
468
469
470
471
472
473
474
475
476
477
478
479
480
481
482
483
484
485
486
487
488
489
490
491
492
493
494
495
496
497
498
499
500
501
502
503
504
505
506
507
508
509
510
511
512
513
514
515
516
517
518
519
520
521
522
523
524
525
526
527
528
529
530
531
532
533
534
535
536
537
538
539
540
541
542
543
|
// SPDX-License-Identifier: GPL-2.0-or-later
/*
* Kernel Probes Jump Optimization (Optprobes)
*
* Copyright (C) IBM Corporation, 2002, 2004
* Copyright (C) Hitachi Ltd., 2012
*/
#include <linux/kprobes.h>
#include <linux/perf_event.h>
#include <linux/ptrace.h>
#include <linux/string.h>
#include <linux/slab.h>
#include <linux/hardirq.h>
#include <linux/preempt.h>
#include <linux/extable.h>
#include <linux/kdebug.h>
#include <linux/kallsyms.h>
#include <linux/ftrace.h>
#include <linux/frame.h>
#include <linux/pgtable.h>
#include <asm/text-patching.h>
#include <asm/cacheflush.h>
#include <asm/desc.h>
#include <linux/uaccess.h>
#include <asm/alternative.h>
#include <asm/insn.h>
#include <asm/debugreg.h>
#include <asm/set_memory.h>
#include <asm/sections.h>
#include <asm/nospec-branch.h>
#include "common.h"
unsigned long __recover_optprobed_insn(kprobe_opcode_t *buf, unsigned long addr)
{
struct optimized_kprobe *op;
struct kprobe *kp;
long offs;
int i;
for (i = 0; i < JMP32_INSN_SIZE; i++) {
kp = get_kprobe((void *)addr - i);
/* This function only handles jump-optimized kprobe */
if (kp && kprobe_optimized(kp)) {
op = container_of(kp, struct optimized_kprobe, kp);
/* If op->list is not empty, op is under optimizing */
if (list_empty(&op->list))
goto found;
}
}
return addr;
found:
/*
* If the kprobe can be optimized, original bytes which can be
* overwritten by jump destination address. In this case, original
* bytes must be recovered from op->optinsn.copied_insn buffer.
*/
if (copy_from_kernel_nofault(buf, (void *)addr,
MAX_INSN_SIZE * sizeof(kprobe_opcode_t)))
return 0UL;
if (addr == (unsigned long)kp->addr) {
buf[0] = kp->opcode;
memcpy(buf + 1, op->optinsn.copied_insn, DISP32_SIZE);
} else {
offs = addr - (unsigned long)kp->addr - 1;
memcpy(buf, op->optinsn.copied_insn + offs, DISP32_SIZE - offs);
}
return (unsigned long)buf;
}
static void synthesize_clac(kprobe_opcode_t *addr)
{
/*
* Can't be static_cpu_has() due to how objtool treats this feature bit.
* This isn't a fast path anyway.
*/
if (!boot_cpu_has(X86_FEATURE_SMAP))
return;
/* Replace the NOP3 with CLAC */
addr[0] = 0x0f;
addr[1] = 0x01;
addr[2] = 0xca;
}
/* Insert a move instruction which sets a pointer to eax/rdi (1st arg). */
static void synthesize_set_arg1(kprobe_opcode_t *addr, unsigned long val)
{
#ifdef CONFIG_X86_64
*addr++ = 0x48;
*addr++ = 0xbf;
#else
*addr++ = 0xb8;
#endif
*(unsigned long *)addr = val;
}
asm (
".pushsection .rodata\n"
"optprobe_template_func:\n"
".global optprobe_template_entry\n"
"optprobe_template_entry:\n"
#ifdef CONFIG_X86_64
/* We don't bother saving the ss register */
" pushq %rsp\n"
" pushfq\n"
".global optprobe_template_clac\n"
"optprobe_template_clac:\n"
ASM_NOP3
SAVE_REGS_STRING
" movq %rsp, %rsi\n"
".global optprobe_template_val\n"
"optprobe_template_val:\n"
ASM_NOP5
ASM_NOP5
".global optprobe_template_call\n"
"optprobe_template_call:\n"
ASM_NOP5
/* Move flags to rsp */
" movq 18*8(%rsp), %rdx\n"
" movq %rdx, 19*8(%rsp)\n"
RESTORE_REGS_STRING
/* Skip flags entry */
" addq $8, %rsp\n"
" popfq\n"
#else /* CONFIG_X86_32 */
" pushl %esp\n"
" pushfl\n"
".global optprobe_template_clac\n"
"optprobe_template_clac:\n"
ASM_NOP3
SAVE_REGS_STRING
" movl %esp, %edx\n"
".global optprobe_template_val\n"
"optprobe_template_val:\n"
ASM_NOP5
".global optprobe_template_call\n"
"optprobe_template_call:\n"
ASM_NOP5
/* Move flags into esp */
" movl 14*4(%esp), %edx\n"
" movl %edx, 15*4(%esp)\n"
RESTORE_REGS_STRING
/* Skip flags entry */
" addl $4, %esp\n"
" popfl\n"
#endif
".global optprobe_template_end\n"
"optprobe_template_end:\n"
".popsection\n");
void optprobe_template_func(void);
STACK_FRAME_NON_STANDARD(optprobe_template_func);
#define TMPL_CLAC_IDX \
((long)optprobe_template_clac - (long)optprobe_template_entry)
#define TMPL_MOVE_IDX \
((long)optprobe_template_val - (long)optprobe_template_entry)
#define TMPL_CALL_IDX \
((long)optprobe_template_call - (long)optprobe_template_entry)
#define TMPL_END_IDX \
((long)optprobe_template_end - (long)optprobe_template_entry)
/* Optimized kprobe call back function: called from optinsn */
static void
optimized_callback(struct optimized_kprobe *op, struct pt_regs *regs)
{
/* This is possible if op is under delayed unoptimizing */
if (kprobe_disabled(&op->kp))
return;
preempt_disable();
if (kprobe_running()) {
kprobes_inc_nmissed_count(&op->kp);
} else {
struct kprobe_ctlblk *kcb = get_kprobe_ctlblk();
/* Save skipped registers */
regs->cs = __KERNEL_CS;
#ifdef CONFIG_X86_32
regs->gs = 0;
#endif
regs->ip = (unsigned long)op->kp.addr + INT3_INSN_SIZE;
regs->orig_ax = ~0UL;
__this_cpu_write(current_kprobe, &op->kp);
kcb->kprobe_status = KPROBE_HIT_ACTIVE;
opt_pre_handler(&op->kp, regs);
__this_cpu_write(current_kprobe, NULL);
}
preempt_enable();
}
NOKPROBE_SYMBOL(optimized_callback);
static int copy_optimized_instructions(u8 *dest, u8 *src, u8 *real)
{
struct insn insn;
int len = 0, ret;
while (len < JMP32_INSN_SIZE) {
ret = __copy_instruction(dest + len, src + len, real + len, &insn);
if (!ret || !can_boost(&insn, src + len))
return -EINVAL;
len += ret;
}
/* Check whether the address range is reserved */
if (ftrace_text_reserved(src, src + len - 1) ||
alternatives_text_reserved(src, src + len - 1) ||
jump_label_text_reserved(src, src + len - 1))
return -EBUSY;
return len;
}
/* Check whether insn is indirect jump */
static int __insn_is_indirect_jump(struct insn *insn)
{
return ((insn->opcode.bytes[0] == 0xff &&
(X86_MODRM_REG(insn->modrm.value) & 6) == 4) || /* Jump */
insn->opcode.bytes[0] == 0xea); /* Segment based jump */
}
/* Check whether insn jumps into specified address range */
static int insn_jump_into_range(struct insn *insn, unsigned long start, int len)
{
unsigned long target = 0;
switch (insn->opcode.bytes[0]) {
case 0xe0: /* loopne */
case 0xe1: /* loope */
case 0xe2: /* loop */
case 0xe3: /* jcxz */
case 0xe9: /* near relative jump */
case 0xeb: /* short relative jump */
break;
case 0x0f:
if ((insn->opcode.bytes[1] & 0xf0) == 0x80) /* jcc near */
break;
return 0;
default:
if ((insn->opcode.bytes[0] & 0xf0) == 0x70) /* jcc short */
break;
return 0;
}
target = (unsigned long)insn->next_byte + insn->immediate.value;
return (start <= target && target <= start + len);
}
static int insn_is_indirect_jump(struct insn *insn)
{
int ret = __insn_is_indirect_jump(insn);
#ifdef CONFIG_RETPOLINE
/*
* Jump to x86_indirect_thunk_* is treated as an indirect jump.
* Note that even with CONFIG_RETPOLINE=y, the kernel compiled with
* older gcc may use indirect jump. So we add this check instead of
* replace indirect-jump check.
*/
if (!ret)
ret = insn_jump_into_range(insn,
(unsigned long)__indirect_thunk_start,
(unsigned long)__indirect_thunk_end -
(unsigned long)__indirect_thunk_start);
#endif
return ret;
}
/* Decode whole function to ensure any instructions don't jump into target */
static int can_optimize(unsigned long paddr)
{
unsigned long addr, size = 0, offset = 0;
struct insn insn;
kprobe_opcode_t buf[MAX_INSN_SIZE];
/* Lookup symbol including addr */
if (!kallsyms_lookup_size_offset(paddr, &size, &offset))
return 0;
/*
* Do not optimize in the entry code due to the unstable
* stack handling and registers setup.
*/
if (((paddr >= (unsigned long)__entry_text_start) &&
(paddr < (unsigned long)__entry_text_end)))
return 0;
/* Check there is enough space for a relative jump. */
if (size - offset < JMP32_INSN_SIZE)
return 0;
/* Decode instructions */
addr = paddr - offset;
while (addr < paddr - offset + size) { /* Decode until function end */
unsigned long recovered_insn;
if (search_exception_tables(addr))
/*
* Since some fixup code will jumps into this function,
* we can't optimize kprobe in this function.
*/
return 0;
recovered_insn = recover_probed_instruction(buf, addr);
if (!recovered_insn)
return 0;
kernel_insn_init(&insn, (void *)recovered_insn, MAX_INSN_SIZE);
insn_get_length(&insn);
/* Another subsystem puts a breakpoint */
if (insn.opcode.bytes[0] == INT3_INSN_OPCODE)
return 0;
/* Recover address */
insn.kaddr = (void *)addr;
insn.next_byte = (void *)(addr + insn.length);
/* Check any instructions don't jump into target */
if (insn_is_indirect_jump(&insn) ||
insn_jump_into_range(&insn, paddr + INT3_INSN_SIZE,
DISP32_SIZE))
return 0;
addr += insn.length;
}
return 1;
}
/* Check optimized_kprobe can actually be optimized. */
int arch_check_optimized_kprobe(struct optimized_kprobe *op)
{
int i;
struct kprobe *p;
for (i = 1; i < op->optinsn.size; i++) {
p = get_kprobe(op->kp.addr + i);
if (p && !kprobe_disabled(p))
return -EEXIST;
}
return 0;
}
/* Check the addr is within the optimized instructions. */
int arch_within_optimized_kprobe(struct optimized_kprobe *op,
unsigned long addr)
{
return ((unsigned long)op->kp.addr <= addr &&
(unsigned long)op->kp.addr + op->optinsn.size > addr);
}
/* Free optimized instruction slot */
static
void __arch_remove_optimized_kprobe(struct optimized_kprobe *op, int dirty)
{
u8 *slot = op->optinsn.insn;
if (slot) {
int len = TMPL_END_IDX + op->optinsn.size + JMP32_INSN_SIZE;
/* Record the perf event before freeing the slot */
if (dirty)
perf_event_text_poke(slot, slot, len, NULL, 0);
free_optinsn_slot(slot, dirty);
op->optinsn.insn = NULL;
op->optinsn.size = 0;
}
}
void arch_remove_optimized_kprobe(struct optimized_kprobe *op)
{
__arch_remove_optimized_kprobe(op, 1);
}
/*
* Copy replacing target instructions
* Target instructions MUST be relocatable (checked inside)
* This is called when new aggr(opt)probe is allocated or reused.
*/
int arch_prepare_optimized_kprobe(struct optimized_kprobe *op,
struct kprobe *__unused)
{
u8 *buf = NULL, *slot;
int ret, len;
long rel;
if (!can_optimize((unsigned long)op->kp.addr))
return -EILSEQ;
buf = kzalloc(MAX_OPTINSN_SIZE, GFP_KERNEL);
if (!buf)
return -ENOMEM;
op->optinsn.insn = slot = get_optinsn_slot();
if (!slot) {
ret = -ENOMEM;
goto out;
}
/*
* Verify if the address gap is in 2GB range, because this uses
* a relative jump.
*/
rel = (long)slot - (long)op->kp.addr + JMP32_INSN_SIZE;
if (abs(rel) > 0x7fffffff) {
ret = -ERANGE;
goto err;
}
/* Copy arch-dep-instance from template */
memcpy(buf, optprobe_template_entry, TMPL_END_IDX);
/* Copy instructions into the out-of-line buffer */
ret = copy_optimized_instructions(buf + TMPL_END_IDX, op->kp.addr,
slot + TMPL_END_IDX);
if (ret < 0)
goto err;
op->optinsn.size = ret;
len = TMPL_END_IDX + op->optinsn.size;
synthesize_clac(buf + TMPL_CLAC_IDX);
/* Set probe information */
synthesize_set_arg1(buf + TMPL_MOVE_IDX, (unsigned long)op);
/* Set probe function call */
synthesize_relcall(buf + TMPL_CALL_IDX,
slot + TMPL_CALL_IDX, optimized_callback);
/* Set returning jmp instruction at the tail of out-of-line buffer */
synthesize_reljump(buf + len, slot + len,
(u8 *)op->kp.addr + op->optinsn.size);
len += JMP32_INSN_SIZE;
/*
* Note len = TMPL_END_IDX + op->optinsn.size + JMP32_INSN_SIZE is also
* used in __arch_remove_optimized_kprobe().
*/
/* We have to use text_poke() for instruction buffer because it is RO */
perf_event_text_poke(slot, NULL, 0, buf, len);
text_poke(slot, buf, len);
ret = 0;
out:
kfree(buf);
return ret;
err:
__arch_remove_optimized_kprobe(op, 0);
goto out;
}
/*
* Replace breakpoints (INT3) with relative jumps (JMP.d32).
* Caller must call with locking kprobe_mutex and text_mutex.
*
* The caller will have installed a regular kprobe and after that issued
* syncrhonize_rcu_tasks(), this ensures that the instruction(s) that live in
* the 4 bytes after the INT3 are unused and can now be overwritten.
*/
void arch_optimize_kprobes(struct list_head *oplist)
{
struct optimized_kprobe *op, *tmp;
u8 insn_buff[JMP32_INSN_SIZE];
list_for_each_entry_safe(op, tmp, oplist, list) {
s32 rel = (s32)((long)op->optinsn.insn -
((long)op->kp.addr + JMP32_INSN_SIZE));
WARN_ON(kprobe_disabled(&op->kp));
/* Backup instructions which will be replaced by jump address */
memcpy(op->optinsn.copied_insn, op->kp.addr + INT3_INSN_SIZE,
DISP32_SIZE);
insn_buff[0] = JMP32_INSN_OPCODE;
*(s32 *)(&insn_buff[1]) = rel;
text_poke_bp(op->kp.addr, insn_buff, JMP32_INSN_SIZE, NULL);
list_del_init(&op->list);
}
}
/*
* Replace a relative jump (JMP.d32) with a breakpoint (INT3).
*
* After that, we can restore the 4 bytes after the INT3 to undo what
* arch_optimize_kprobes() scribbled. This is safe since those bytes will be
* unused once the INT3 lands.
*/
void arch_unoptimize_kprobe(struct optimized_kprobe *op)
{
u8 new[JMP32_INSN_SIZE] = { INT3_INSN_OPCODE, };
u8 old[JMP32_INSN_SIZE];
u8 *addr = op->kp.addr;
memcpy(old, op->kp.addr, JMP32_INSN_SIZE);
memcpy(new + INT3_INSN_SIZE,
op->optinsn.copied_insn,
JMP32_INSN_SIZE - INT3_INSN_SIZE);
text_poke(addr, new, INT3_INSN_SIZE);
text_poke_sync();
text_poke(addr + INT3_INSN_SIZE,
new + INT3_INSN_SIZE,
JMP32_INSN_SIZE - INT3_INSN_SIZE);
text_poke_sync();
perf_event_text_poke(op->kp.addr, old, JMP32_INSN_SIZE, new, JMP32_INSN_SIZE);
}
/*
* Recover original instructions and breakpoints from relative jumps.
* Caller must call with locking kprobe_mutex.
*/
extern void arch_unoptimize_kprobes(struct list_head *oplist,
struct list_head *done_list)
{
struct optimized_kprobe *op, *tmp;
list_for_each_entry_safe(op, tmp, oplist, list) {
arch_unoptimize_kprobe(op);
list_move(&op->list, done_list);
}
}
int setup_detour_execution(struct kprobe *p, struct pt_regs *regs, int reenter)
{
struct optimized_kprobe *op;
if (p->flags & KPROBE_FLAG_OPTIMIZED) {
/* This kprobe is really able to run optimized path. */
op = container_of(p, struct optimized_kprobe, kp);
/* Detour through copied instructions */
regs->ip = (unsigned long)op->optinsn.insn + TMPL_END_IDX;
if (!reenter)
reset_current_kprobe();
return 1;
}
return 0;
}
NOKPROBE_SYMBOL(setup_detour_execution);
|