1// SPDX-License-Identifier: GPL-2.0-or-later
2/*
3 * Kernel Probes (KProbes)
4 *
5 * Copyright (C) IBM Corporation, 2002, 2004
6 *
7 * 2002-Oct Created by Vamsi Krishna S <vamsi_krishna@in.ibm.com> Kernel
8 * Probes initial implementation ( includes contributions from
9 * Rusty Russell).
10 * 2004-July Suparna Bhattacharya <suparna@in.ibm.com> added jumper probes
11 * interface to access function arguments.
12 * 2004-Oct Jim Keniston <jkenisto@us.ibm.com> and Prasanna S Panchamukhi
13 * <prasanna@in.ibm.com> adapted for x86_64 from i386.
14 * 2005-Mar Roland McGrath <roland@redhat.com>
15 * Fixed to handle %rip-relative addressing mode correctly.
16 * 2005-May Hien Nguyen <hien@us.ibm.com>, Jim Keniston
17 * <jkenisto@us.ibm.com> and Prasanna S Panchamukhi
18 * <prasanna@in.ibm.com> added function-return probes.
19 * 2005-May Rusty Lynch <rusty.lynch@intel.com>
20 * Added function return probes functionality
21 * 2006-Feb Masami Hiramatsu <hiramatu@sdl.hitachi.co.jp> added
22 * kprobe-booster and kretprobe-booster for i386.
23 * 2007-Dec Masami Hiramatsu <mhiramat@redhat.com> added kprobe-booster
24 * and kretprobe-booster for x86-64
25 * 2007-Dec Masami Hiramatsu <mhiramat@redhat.com>, Arjan van de Ven
26 * <arjan@infradead.org> and Jim Keniston <jkenisto@us.ibm.com>
27 * unified x86 kprobes code.
28 */
29#include <linux/kprobes.h>
30#include <linux/ptrace.h>
31#include <linux/string.h>
32#include <linux/slab.h>
33#include <linux/hardirq.h>
34#include <linux/preempt.h>
35#include <linux/sched/debug.h>
36#include <linux/perf_event.h>
37#include <linux/extable.h>
38#include <linux/kdebug.h>
39#include <linux/kallsyms.h>
40#include <linux/kgdb.h>
41#include <linux/ftrace.h>
42#include <linux/kasan.h>
43#include <linux/moduleloader.h>
44#include <linux/objtool.h>
45#include <linux/vmalloc.h>
46#include <linux/pgtable.h>
47#include <linux/set_memory.h>
48#include <linux/cfi.h>
49
50#include <asm/text-patching.h>
51#include <asm/cacheflush.h>
52#include <asm/desc.h>
53#include <linux/uaccess.h>
54#include <asm/alternative.h>
55#include <asm/insn.h>
56#include <asm/debugreg.h>
57#include <asm/ibt.h>
58
59#include "common.h"
60
61DEFINE_PER_CPU(struct kprobe *, current_kprobe) = NULL;
62DEFINE_PER_CPU(struct kprobe_ctlblk, kprobe_ctlblk);
63
64#define W(row, b0, b1, b2, b3, b4, b5, b6, b7, b8, b9, ba, bb, bc, bd, be, bf)\
65 (((b0##UL << 0x0)|(b1##UL << 0x1)|(b2##UL << 0x2)|(b3##UL << 0x3) | \
66 (b4##UL << 0x4)|(b5##UL << 0x5)|(b6##UL << 0x6)|(b7##UL << 0x7) | \
67 (b8##UL << 0x8)|(b9##UL << 0x9)|(ba##UL << 0xa)|(bb##UL << 0xb) | \
68 (bc##UL << 0xc)|(bd##UL << 0xd)|(be##UL << 0xe)|(bf##UL << 0xf)) \
69 << (row % 32))
70 /*
71 * Undefined/reserved opcodes, conditional jump, Opcode Extension
72 * Groups, and some special opcodes can not boost.
73 * This is non-const and volatile to keep gcc from statically
74 * optimizing it out, as variable_test_bit makes gcc think only
75 * *(unsigned long*) is used.
76 */
77static volatile u32 twobyte_is_boostable[256 / 32] = {
78 /* 0 1 2 3 4 5 6 7 8 9 a b c d e f */
79 /* ---------------------------------------------- */
80 W(0x00, 0, 0, 1, 1, 0, 0, 1, 0, 1, 1, 0, 0, 0, 0, 0, 0) | /* 00 */
81 W(0x10, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 1) , /* 10 */
82 W(0x20, 1, 1, 1, 1, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0) | /* 20 */
83 W(0x30, 0, 1, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0) , /* 30 */
84 W(0x40, 1, 1, 1, 1, 1, 1, 1, 1, 1, 1, 1, 1, 1, 1, 1, 1) | /* 40 */
85 W(0x50, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0) , /* 50 */
86 W(0x60, 1, 1, 1, 1, 1, 1, 1, 1, 1, 1, 1, 1, 0, 0, 1, 1) | /* 60 */
87 W(0x70, 0, 0, 0, 0, 1, 1, 1, 1, 0, 0, 0, 0, 0, 0, 1, 1) , /* 70 */
88 W(0x80, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0) | /* 80 */
89 W(0x90, 1, 1, 1, 1, 1, 1, 1, 1, 1, 1, 1, 1, 1, 1, 1, 1) , /* 90 */
90 W(0xa0, 1, 1, 0, 1, 1, 1, 0, 0, 1, 1, 0, 1, 1, 1, 0, 1) | /* a0 */
91 W(0xb0, 1, 1, 1, 1, 1, 1, 1, 1, 0, 0, 0, 1, 1, 1, 1, 1) , /* b0 */
92 W(0xc0, 1, 1, 0, 0, 0, 0, 0, 0, 1, 1, 1, 1, 1, 1, 1, 1) | /* c0 */
93 W(0xd0, 0, 1, 1, 1, 0, 1, 0, 0, 1, 1, 0, 1, 1, 1, 0, 1) , /* d0 */
94 W(0xe0, 0, 1, 1, 0, 0, 1, 0, 0, 1, 1, 0, 1, 1, 1, 0, 1) | /* e0 */
95 W(0xf0, 0, 1, 1, 1, 0, 1, 0, 0, 1, 1, 1, 0, 1, 1, 1, 0) /* f0 */
96 /* ----------------------------------------------- */
97 /* 0 1 2 3 4 5 6 7 8 9 a b c d e f */
98};
99#undef W
100
101struct kretprobe_blackpoint kretprobe_blacklist[] = {
102 {"__switch_to", }, /* This function switches only current task, but
103 doesn't switch kernel stack.*/
104 {NULL, NULL} /* Terminator */
105};
106
107const int kretprobe_blacklist_size = ARRAY_SIZE(kretprobe_blacklist);
108
109static nokprobe_inline void
110__synthesize_relative_insn(void *dest, void *from, void *to, u8 op)
111{
112 struct __arch_relative_insn {
113 u8 op;
114 s32 raddr;
115 } __packed *insn;
116
117 insn = (struct __arch_relative_insn *)dest;
118 insn->raddr = (s32)((long)(to) - ((long)(from) + 5));
119 insn->op = op;
120}
121
122/* Insert a jump instruction at address 'from', which jumps to address 'to'.*/
123void synthesize_reljump(void *dest, void *from, void *to)
124{
125 __synthesize_relative_insn(dest, from, to, JMP32_INSN_OPCODE);
126}
127NOKPROBE_SYMBOL(synthesize_reljump);
128
129/* Insert a call instruction at address 'from', which calls address 'to'.*/
130void synthesize_relcall(void *dest, void *from, void *to)
131{
132 __synthesize_relative_insn(dest, from, to, CALL_INSN_OPCODE);
133}
134NOKPROBE_SYMBOL(synthesize_relcall);
135
136/*
137 * Returns non-zero if INSN is boostable.
138 * RIP relative instructions are adjusted at copying time in 64 bits mode
139 */
140int can_boost(struct insn *insn, void *addr)
141{
142 kprobe_opcode_t opcode;
143 insn_byte_t prefix;
144 int i;
145
146 if (search_exception_tables(add: (unsigned long)addr))
147 return 0; /* Page fault may occur on this address. */
148
149 /* 2nd-byte opcode */
150 if (insn->opcode.nbytes == 2)
151 return test_bit(insn->opcode.bytes[1],
152 (unsigned long *)twobyte_is_boostable);
153
154 if (insn->opcode.nbytes != 1)
155 return 0;
156
157 for_each_insn_prefix(insn, i, prefix) {
158 insn_attr_t attr;
159
160 attr = inat_get_opcode_attribute(opcode: prefix);
161 /* Can't boost Address-size override prefix and CS override prefix */
162 if (prefix == 0x2e || inat_is_address_size_prefix(attr))
163 return 0;
164 }
165
166 opcode = insn->opcode.bytes[0];
167
168 switch (opcode) {
169 case 0x62: /* bound */
170 case 0x70 ... 0x7f: /* Conditional jumps */
171 case 0x9a: /* Call far */
172 case 0xc0 ... 0xc1: /* Grp2 */
173 case 0xcc ... 0xce: /* software exceptions */
174 case 0xd0 ... 0xd3: /* Grp2 */
175 case 0xd6: /* (UD) */
176 case 0xd8 ... 0xdf: /* ESC */
177 case 0xe0 ... 0xe3: /* LOOP*, JCXZ */
178 case 0xe8 ... 0xe9: /* near Call, JMP */
179 case 0xeb: /* Short JMP */
180 case 0xf0 ... 0xf4: /* LOCK/REP, HLT */
181 case 0xf6 ... 0xf7: /* Grp3 */
182 case 0xfe: /* Grp4 */
183 /* ... are not boostable */
184 return 0;
185 case 0xff: /* Grp5 */
186 /* Only indirect jmp is boostable */
187 return X86_MODRM_REG(insn->modrm.bytes[0]) == 4;
188 default:
189 return 1;
190 }
191}
192
193static unsigned long
194__recover_probed_insn(kprobe_opcode_t *buf, unsigned long addr)
195{
196 struct kprobe *kp;
197 bool faddr;
198
199 kp = get_kprobe(addr: (void *)addr);
200 faddr = ftrace_location(ip: addr) == addr;
201 /*
202 * Use the current code if it is not modified by Kprobe
203 * and it cannot be modified by ftrace.
204 */
205 if (!kp && !faddr)
206 return addr;
207
208 /*
209 * Basically, kp->ainsn.insn has an original instruction.
210 * However, RIP-relative instruction can not do single-stepping
211 * at different place, __copy_instruction() tweaks the displacement of
212 * that instruction. In that case, we can't recover the instruction
213 * from the kp->ainsn.insn.
214 *
215 * On the other hand, in case on normal Kprobe, kp->opcode has a copy
216 * of the first byte of the probed instruction, which is overwritten
217 * by int3. And the instruction at kp->addr is not modified by kprobes
218 * except for the first byte, we can recover the original instruction
219 * from it and kp->opcode.
220 *
221 * In case of Kprobes using ftrace, we do not have a copy of
222 * the original instruction. In fact, the ftrace location might
223 * be modified at anytime and even could be in an inconsistent state.
224 * Fortunately, we know that the original code is the ideal 5-byte
225 * long NOP.
226 */
227 if (copy_from_kernel_nofault(dst: buf, src: (void *)addr,
228 MAX_INSN_SIZE * sizeof(kprobe_opcode_t)))
229 return 0UL;
230
231 if (faddr)
232 memcpy(buf, x86_nops[5], 5);
233 else
234 buf[0] = kp->opcode;
235 return (unsigned long)buf;
236}
237
238/*
239 * Recover the probed instruction at addr for further analysis.
240 * Caller must lock kprobes by kprobe_mutex, or disable preemption
241 * for preventing to release referencing kprobes.
242 * Returns zero if the instruction can not get recovered (or access failed).
243 */
244unsigned long recover_probed_instruction(kprobe_opcode_t *buf, unsigned long addr)
245{
246 unsigned long __addr;
247
248 __addr = __recover_optprobed_insn(buf, addr);
249 if (__addr != addr)
250 return __addr;
251
252 return __recover_probed_insn(buf, addr);
253}
254
255/* Check if paddr is at an instruction boundary */
256static int can_probe(unsigned long paddr)
257{
258 unsigned long addr, __addr, offset = 0;
259 struct insn insn;
260 kprobe_opcode_t buf[MAX_INSN_SIZE];
261
262 if (!kallsyms_lookup_size_offset(addr: paddr, NULL, offset: &offset))
263 return 0;
264
265 /* Decode instructions */
266 addr = paddr - offset;
267 while (addr < paddr) {
268 int ret;
269
270 /*
271 * Check if the instruction has been modified by another
272 * kprobe, in which case we replace the breakpoint by the
273 * original instruction in our buffer.
274 * Also, jump optimization will change the breakpoint to
275 * relative-jump. Since the relative-jump itself is
276 * normally used, we just go through if there is no kprobe.
277 */
278 __addr = recover_probed_instruction(buf, addr);
279 if (!__addr)
280 return 0;
281
282 ret = insn_decode_kernel(&insn, (void *)__addr);
283 if (ret < 0)
284 return 0;
285
286#ifdef CONFIG_KGDB
287 /*
288 * If there is a dynamically installed kgdb sw breakpoint,
289 * this function should not be probed.
290 */
291 if (insn.opcode.bytes[0] == INT3_INSN_OPCODE &&
292 kgdb_has_hit_break(addr))
293 return 0;
294#endif
295 addr += insn.length;
296 }
297 if (IS_ENABLED(CONFIG_CFI_CLANG)) {
298 /*
299 * The compiler generates the following instruction sequence
300 * for indirect call checks and cfi.c decodes this;
301 *
302 *  movl -<id>, %r10d ; 6 bytes
303 * addl -4(%reg), %r10d ; 4 bytes
304 * je .Ltmp1 ; 2 bytes
305 * ud2 ; <- regs->ip
306 * .Ltmp1:
307 *
308 * Also, these movl and addl are used for showing expected
309 * type. So those must not be touched.
310 */
311 __addr = recover_probed_instruction(buf, addr);
312 if (!__addr)
313 return 0;
314
315 if (insn_decode_kernel(&insn, (void *)__addr) < 0)
316 return 0;
317
318 if (insn.opcode.value == 0xBA)
319 offset = 12;
320 else if (insn.opcode.value == 0x3)
321 offset = 6;
322 else
323 goto out;
324
325 /* This movl/addl is used for decoding CFI. */
326 if (is_cfi_trap(addr: addr + offset))
327 return 0;
328 }
329
330out:
331 return (addr == paddr);
332}
333
334/* If x86 supports IBT (ENDBR) it must be skipped. */
335kprobe_opcode_t *arch_adjust_kprobe_addr(unsigned long addr, unsigned long offset,
336 bool *on_func_entry)
337{
338 if (is_endbr(val: *(u32 *)addr)) {
339 *on_func_entry = !offset || offset == 4;
340 if (*on_func_entry)
341 offset = 4;
342
343 } else {
344 *on_func_entry = !offset;
345 }
346
347 return (kprobe_opcode_t *)(addr + offset);
348}
349
350/*
351 * Copy an instruction with recovering modified instruction by kprobes
352 * and adjust the displacement if the instruction uses the %rip-relative
353 * addressing mode. Note that since @real will be the final place of copied
354 * instruction, displacement must be adjust by @real, not @dest.
355 * This returns the length of copied instruction, or 0 if it has an error.
356 */
357int __copy_instruction(u8 *dest, u8 *src, u8 *real, struct insn *insn)
358{
359 kprobe_opcode_t buf[MAX_INSN_SIZE];
360 unsigned long recovered_insn = recover_probed_instruction(buf, addr: (unsigned long)src);
361 int ret;
362
363 if (!recovered_insn || !insn)
364 return 0;
365
366 /* This can access kernel text if given address is not recovered */
367 if (copy_from_kernel_nofault(dst: dest, src: (void *)recovered_insn,
368 MAX_INSN_SIZE))
369 return 0;
370
371 ret = insn_decode_kernel(insn, dest);
372 if (ret < 0)
373 return 0;
374
375 /* We can not probe force emulate prefixed instruction */
376 if (insn_has_emulate_prefix(insn))
377 return 0;
378
379 /* Another subsystem puts a breakpoint, failed to recover */
380 if (insn->opcode.bytes[0] == INT3_INSN_OPCODE)
381 return 0;
382
383 /* We should not singlestep on the exception masking instructions */
384 if (insn_masking_exception(insn))
385 return 0;
386
387#ifdef CONFIG_X86_64
388 /* Only x86_64 has RIP relative instructions */
389 if (insn_rip_relative(insn)) {
390 s64 newdisp;
391 u8 *disp;
392 /*
393 * The copied instruction uses the %rip-relative addressing
394 * mode. Adjust the displacement for the difference between
395 * the original location of this instruction and the location
396 * of the copy that will actually be run. The tricky bit here
397 * is making sure that the sign extension happens correctly in
398 * this calculation, since we need a signed 32-bit result to
399 * be sign-extended to 64 bits when it's added to the %rip
400 * value and yield the same 64-bit result that the sign-
401 * extension of the original signed 32-bit displacement would
402 * have given.
403 */
404 newdisp = (u8 *) src + (s64) insn->displacement.value
405 - (u8 *) real;
406 if ((s64) (s32) newdisp != newdisp) {
407 pr_err("Kprobes error: new displacement does not fit into s32 (%llx)\n", newdisp);
408 return 0;
409 }
410 disp = (u8 *) dest + insn_offset_displacement(insn);
411 *(s32 *) disp = (s32) newdisp;
412 }
413#endif
414 return insn->length;
415}
416
417/* Prepare reljump or int3 right after instruction */
418static int prepare_singlestep(kprobe_opcode_t *buf, struct kprobe *p,
419 struct insn *insn)
420{
421 int len = insn->length;
422
423 if (!IS_ENABLED(CONFIG_PREEMPTION) &&
424 !p->post_handler && can_boost(insn, addr: p->addr) &&
425 MAX_INSN_SIZE - len >= JMP32_INSN_SIZE) {
426 /*
427 * These instructions can be executed directly if it
428 * jumps back to correct address.
429 */
430 synthesize_reljump(dest: buf + len, from: p->ainsn.insn + len,
431 to: p->addr + insn->length);
432 len += JMP32_INSN_SIZE;
433 p->ainsn.boostable = 1;
434 } else {
435 /* Otherwise, put an int3 for trapping singlestep */
436 if (MAX_INSN_SIZE - len < INT3_INSN_SIZE)
437 return -ENOSPC;
438
439 buf[len] = INT3_INSN_OPCODE;
440 len += INT3_INSN_SIZE;
441 }
442
443 return len;
444}
445
446/* Make page to RO mode when allocate it */
447void *alloc_insn_page(void)
448{
449 void *page;
450
451 page = module_alloc(PAGE_SIZE);
452 if (!page)
453 return NULL;
454
455 /*
456 * TODO: Once additional kernel code protection mechanisms are set, ensure
457 * that the page was not maliciously altered and it is still zeroed.
458 */
459 set_memory_rox(addr: (unsigned long)page, numpages: 1);
460
461 return page;
462}
463
464/* Kprobe x86 instruction emulation - only regs->ip or IF flag modifiers */
465
466static void kprobe_emulate_ifmodifiers(struct kprobe *p, struct pt_regs *regs)
467{
468 switch (p->ainsn.opcode) {
469 case 0xfa: /* cli */
470 regs->flags &= ~(X86_EFLAGS_IF);
471 break;
472 case 0xfb: /* sti */
473 regs->flags |= X86_EFLAGS_IF;
474 break;
475 case 0x9c: /* pushf */
476 int3_emulate_push(regs, val: regs->flags);
477 break;
478 case 0x9d: /* popf */
479 regs->flags = int3_emulate_pop(regs);
480 break;
481 }
482 regs->ip = regs->ip - INT3_INSN_SIZE + p->ainsn.size;
483}
484NOKPROBE_SYMBOL(kprobe_emulate_ifmodifiers);
485
486static void kprobe_emulate_ret(struct kprobe *p, struct pt_regs *regs)
487{
488 int3_emulate_ret(regs);
489}
490NOKPROBE_SYMBOL(kprobe_emulate_ret);
491
492static void kprobe_emulate_call(struct kprobe *p, struct pt_regs *regs)
493{
494 unsigned long func = regs->ip - INT3_INSN_SIZE + p->ainsn.size;
495
496 func += p->ainsn.rel32;
497 int3_emulate_call(regs, func);
498}
499NOKPROBE_SYMBOL(kprobe_emulate_call);
500
501static void kprobe_emulate_jmp(struct kprobe *p, struct pt_regs *regs)
502{
503 unsigned long ip = regs->ip - INT3_INSN_SIZE + p->ainsn.size;
504
505 ip += p->ainsn.rel32;
506 int3_emulate_jmp(regs, ip);
507}
508NOKPROBE_SYMBOL(kprobe_emulate_jmp);
509
510static void kprobe_emulate_jcc(struct kprobe *p, struct pt_regs *regs)
511{
512 unsigned long ip = regs->ip - INT3_INSN_SIZE + p->ainsn.size;
513
514 int3_emulate_jcc(regs, cc: p->ainsn.jcc.type, ip, disp: p->ainsn.rel32);
515}
516NOKPROBE_SYMBOL(kprobe_emulate_jcc);
517
518static void kprobe_emulate_loop(struct kprobe *p, struct pt_regs *regs)
519{
520 unsigned long ip = regs->ip - INT3_INSN_SIZE + p->ainsn.size;
521 bool match;
522
523 if (p->ainsn.loop.type != 3) { /* LOOP* */
524 if (p->ainsn.loop.asize == 32)
525 match = ((*(u32 *)&regs->cx)--) != 0;
526#ifdef CONFIG_X86_64
527 else if (p->ainsn.loop.asize == 64)
528 match = ((*(u64 *)&regs->cx)--) != 0;
529#endif
530 else
531 match = ((*(u16 *)&regs->cx)--) != 0;
532 } else { /* JCXZ */
533 if (p->ainsn.loop.asize == 32)
534 match = *(u32 *)(&regs->cx) == 0;
535#ifdef CONFIG_X86_64
536 else if (p->ainsn.loop.asize == 64)
537 match = *(u64 *)(&regs->cx) == 0;
538#endif
539 else
540 match = *(u16 *)(&regs->cx) == 0;
541 }
542
543 if (p->ainsn.loop.type == 0) /* LOOPNE */
544 match = match && !(regs->flags & X86_EFLAGS_ZF);
545 else if (p->ainsn.loop.type == 1) /* LOOPE */
546 match = match && (regs->flags & X86_EFLAGS_ZF);
547
548 if (match)
549 ip += p->ainsn.rel32;
550 int3_emulate_jmp(regs, ip);
551}
552NOKPROBE_SYMBOL(kprobe_emulate_loop);
553
554static const int addrmode_regoffs[] = {
555 offsetof(struct pt_regs, ax),
556 offsetof(struct pt_regs, cx),
557 offsetof(struct pt_regs, dx),
558 offsetof(struct pt_regs, bx),
559 offsetof(struct pt_regs, sp),
560 offsetof(struct pt_regs, bp),
561 offsetof(struct pt_regs, si),
562 offsetof(struct pt_regs, di),
563#ifdef CONFIG_X86_64
564 offsetof(struct pt_regs, r8),
565 offsetof(struct pt_regs, r9),
566 offsetof(struct pt_regs, r10),
567 offsetof(struct pt_regs, r11),
568 offsetof(struct pt_regs, r12),
569 offsetof(struct pt_regs, r13),
570 offsetof(struct pt_regs, r14),
571 offsetof(struct pt_regs, r15),
572#endif
573};
574
575static void kprobe_emulate_call_indirect(struct kprobe *p, struct pt_regs *regs)
576{
577 unsigned long offs = addrmode_regoffs[p->ainsn.indirect.reg];
578
579 int3_emulate_call(regs, func: regs_get_register(regs, offset: offs));
580}
581NOKPROBE_SYMBOL(kprobe_emulate_call_indirect);
582
583static void kprobe_emulate_jmp_indirect(struct kprobe *p, struct pt_regs *regs)
584{
585 unsigned long offs = addrmode_regoffs[p->ainsn.indirect.reg];
586
587 int3_emulate_jmp(regs, ip: regs_get_register(regs, offset: offs));
588}
589NOKPROBE_SYMBOL(kprobe_emulate_jmp_indirect);
590
591static int prepare_emulation(struct kprobe *p, struct insn *insn)
592{
593 insn_byte_t opcode = insn->opcode.bytes[0];
594
595 switch (opcode) {
596 case 0xfa: /* cli */
597 case 0xfb: /* sti */
598 case 0x9c: /* pushfl */
599 case 0x9d: /* popf/popfd */
600 /*
601 * IF modifiers must be emulated since it will enable interrupt while
602 * int3 single stepping.
603 */
604 p->ainsn.emulate_op = kprobe_emulate_ifmodifiers;
605 p->ainsn.opcode = opcode;
606 break;
607 case 0xc2: /* ret/lret */
608 case 0xc3:
609 case 0xca:
610 case 0xcb:
611 p->ainsn.emulate_op = kprobe_emulate_ret;
612 break;
613 case 0x9a: /* far call absolute -- segment is not supported */
614 case 0xea: /* far jmp absolute -- segment is not supported */
615 case 0xcc: /* int3 */
616 case 0xcf: /* iret -- in-kernel IRET is not supported */
617 return -EOPNOTSUPP;
618 break;
619 case 0xe8: /* near call relative */
620 p->ainsn.emulate_op = kprobe_emulate_call;
621 if (insn->immediate.nbytes == 2)
622 p->ainsn.rel32 = *(s16 *)&insn->immediate.value;
623 else
624 p->ainsn.rel32 = *(s32 *)&insn->immediate.value;
625 break;
626 case 0xeb: /* short jump relative */
627 case 0xe9: /* near jump relative */
628 p->ainsn.emulate_op = kprobe_emulate_jmp;
629 if (insn->immediate.nbytes == 1)
630 p->ainsn.rel32 = *(s8 *)&insn->immediate.value;
631 else if (insn->immediate.nbytes == 2)
632 p->ainsn.rel32 = *(s16 *)&insn->immediate.value;
633 else
634 p->ainsn.rel32 = *(s32 *)&insn->immediate.value;
635 break;
636 case 0x70 ... 0x7f:
637 /* 1 byte conditional jump */
638 p->ainsn.emulate_op = kprobe_emulate_jcc;
639 p->ainsn.jcc.type = opcode & 0xf;
640 p->ainsn.rel32 = insn->immediate.value;
641 break;
642 case 0x0f:
643 opcode = insn->opcode.bytes[1];
644 if ((opcode & 0xf0) == 0x80) {
645 /* 2 bytes Conditional Jump */
646 p->ainsn.emulate_op = kprobe_emulate_jcc;
647 p->ainsn.jcc.type = opcode & 0xf;
648 if (insn->immediate.nbytes == 2)
649 p->ainsn.rel32 = *(s16 *)&insn->immediate.value;
650 else
651 p->ainsn.rel32 = *(s32 *)&insn->immediate.value;
652 } else if (opcode == 0x01 &&
653 X86_MODRM_REG(insn->modrm.bytes[0]) == 0 &&
654 X86_MODRM_MOD(insn->modrm.bytes[0]) == 3) {
655 /* VM extensions - not supported */
656 return -EOPNOTSUPP;
657 }
658 break;
659 case 0xe0: /* Loop NZ */
660 case 0xe1: /* Loop */
661 case 0xe2: /* Loop */
662 case 0xe3: /* J*CXZ */
663 p->ainsn.emulate_op = kprobe_emulate_loop;
664 p->ainsn.loop.type = opcode & 0x3;
665 p->ainsn.loop.asize = insn->addr_bytes * 8;
666 p->ainsn.rel32 = *(s8 *)&insn->immediate.value;
667 break;
668 case 0xff:
669 /*
670 * Since the 0xff is an extended group opcode, the instruction
671 * is determined by the MOD/RM byte.
672 */
673 opcode = insn->modrm.bytes[0];
674 switch (X86_MODRM_REG(opcode)) {
675 case 0b010: /* FF /2, call near, absolute indirect */
676 p->ainsn.emulate_op = kprobe_emulate_call_indirect;
677 break;
678 case 0b100: /* FF /4, jmp near, absolute indirect */
679 p->ainsn.emulate_op = kprobe_emulate_jmp_indirect;
680 break;
681 case 0b011: /* FF /3, call far, absolute indirect */
682 case 0b101: /* FF /5, jmp far, absolute indirect */
683 return -EOPNOTSUPP;
684 }
685
686 if (!p->ainsn.emulate_op)
687 break;
688
689 if (insn->addr_bytes != sizeof(unsigned long))
690 return -EOPNOTSUPP; /* Don't support different size */
691 if (X86_MODRM_MOD(opcode) != 3)
692 return -EOPNOTSUPP; /* TODO: support memory addressing */
693
694 p->ainsn.indirect.reg = X86_MODRM_RM(opcode);
695#ifdef CONFIG_X86_64
696 if (X86_REX_B(insn->rex_prefix.value))
697 p->ainsn.indirect.reg += 8;
698#endif
699 break;
700 default:
701 break;
702 }
703 p->ainsn.size = insn->length;
704
705 return 0;
706}
707
708static int arch_copy_kprobe(struct kprobe *p)
709{
710 struct insn insn;
711 kprobe_opcode_t buf[MAX_INSN_SIZE];
712 int ret, len;
713
714 /* Copy an instruction with recovering if other optprobe modifies it.*/
715 len = __copy_instruction(dest: buf, src: p->addr, real: p->ainsn.insn, insn: &insn);
716 if (!len)
717 return -EINVAL;
718
719 /* Analyze the opcode and setup emulate functions */
720 ret = prepare_emulation(p, insn: &insn);
721 if (ret < 0)
722 return ret;
723
724 /* Add int3 for single-step or booster jmp */
725 len = prepare_singlestep(buf, p, insn: &insn);
726 if (len < 0)
727 return len;
728
729 /* Also, displacement change doesn't affect the first byte */
730 p->opcode = buf[0];
731
732 p->ainsn.tp_len = len;
733 perf_event_text_poke(addr: p->ainsn.insn, NULL, old_len: 0, new_bytes: buf, new_len: len);
734
735 /* OK, write back the instruction(s) into ROX insn buffer */
736 text_poke(addr: p->ainsn.insn, opcode: buf, len);
737
738 return 0;
739}
740
741int arch_prepare_kprobe(struct kprobe *p)
742{
743 int ret;
744
745 if (alternatives_text_reserved(start: p->addr, end: p->addr))
746 return -EINVAL;
747
748 if (!can_probe(paddr: (unsigned long)p->addr))
749 return -EILSEQ;
750
751 memset(&p->ainsn, 0, sizeof(p->ainsn));
752
753 /* insn: must be on special executable page on x86. */
754 p->ainsn.insn = get_insn_slot();
755 if (!p->ainsn.insn)
756 return -ENOMEM;
757
758 ret = arch_copy_kprobe(p);
759 if (ret) {
760 free_insn_slot(slot: p->ainsn.insn, dirty: 0);
761 p->ainsn.insn = NULL;
762 }
763
764 return ret;
765}
766
767void arch_arm_kprobe(struct kprobe *p)
768{
769 u8 int3 = INT3_INSN_OPCODE;
770
771 text_poke(addr: p->addr, opcode: &int3, len: 1);
772 text_poke_sync();
773 perf_event_text_poke(addr: p->addr, old_bytes: &p->opcode, old_len: 1, new_bytes: &int3, new_len: 1);
774}
775
776void arch_disarm_kprobe(struct kprobe *p)
777{
778 u8 int3 = INT3_INSN_OPCODE;
779
780 perf_event_text_poke(addr: p->addr, old_bytes: &int3, old_len: 1, new_bytes: &p->opcode, new_len: 1);
781 text_poke(addr: p->addr, opcode: &p->opcode, len: 1);
782 text_poke_sync();
783}
784
785void arch_remove_kprobe(struct kprobe *p)
786{
787 if (p->ainsn.insn) {
788 /* Record the perf event before freeing the slot */
789 perf_event_text_poke(addr: p->ainsn.insn, old_bytes: p->ainsn.insn,
790 old_len: p->ainsn.tp_len, NULL, new_len: 0);
791 free_insn_slot(slot: p->ainsn.insn, dirty: p->ainsn.boostable);
792 p->ainsn.insn = NULL;
793 }
794}
795
796static nokprobe_inline void
797save_previous_kprobe(struct kprobe_ctlblk *kcb)
798{
799 kcb->prev_kprobe.kp = kprobe_running();
800 kcb->prev_kprobe.status = kcb->kprobe_status;
801 kcb->prev_kprobe.old_flags = kcb->kprobe_old_flags;
802 kcb->prev_kprobe.saved_flags = kcb->kprobe_saved_flags;
803}
804
805static nokprobe_inline void
806restore_previous_kprobe(struct kprobe_ctlblk *kcb)
807{
808 __this_cpu_write(current_kprobe, kcb->prev_kprobe.kp);
809 kcb->kprobe_status = kcb->prev_kprobe.status;
810 kcb->kprobe_old_flags = kcb->prev_kprobe.old_flags;
811 kcb->kprobe_saved_flags = kcb->prev_kprobe.saved_flags;
812}
813
814static nokprobe_inline void
815set_current_kprobe(struct kprobe *p, struct pt_regs *regs,
816 struct kprobe_ctlblk *kcb)
817{
818 __this_cpu_write(current_kprobe, p);
819 kcb->kprobe_saved_flags = kcb->kprobe_old_flags
820 = (regs->flags & X86_EFLAGS_IF);
821}
822
823static void kprobe_post_process(struct kprobe *cur, struct pt_regs *regs,
824 struct kprobe_ctlblk *kcb)
825{
826 /* Restore back the original saved kprobes variables and continue. */
827 if (kcb->kprobe_status == KPROBE_REENTER) {
828 /* This will restore both kcb and current_kprobe */
829 restore_previous_kprobe(kcb);
830 } else {
831 /*
832 * Always update the kcb status because
833 * reset_curent_kprobe() doesn't update kcb.
834 */
835 kcb->kprobe_status = KPROBE_HIT_SSDONE;
836 if (cur->post_handler)
837 cur->post_handler(cur, regs, 0);
838 reset_current_kprobe();
839 }
840}
841NOKPROBE_SYMBOL(kprobe_post_process);
842
843static void setup_singlestep(struct kprobe *p, struct pt_regs *regs,
844 struct kprobe_ctlblk *kcb, int reenter)
845{
846 if (setup_detour_execution(p, regs, reenter))
847 return;
848
849#if !defined(CONFIG_PREEMPTION)
850 if (p->ainsn.boostable) {
851 /* Boost up -- we can execute copied instructions directly */
852 if (!reenter)
853 reset_current_kprobe();
854 /*
855 * Reentering boosted probe doesn't reset current_kprobe,
856 * nor set current_kprobe, because it doesn't use single
857 * stepping.
858 */
859 regs->ip = (unsigned long)p->ainsn.insn;
860 return;
861 }
862#endif
863 if (reenter) {
864 save_previous_kprobe(kcb);
865 set_current_kprobe(p, regs, kcb);
866 kcb->kprobe_status = KPROBE_REENTER;
867 } else
868 kcb->kprobe_status = KPROBE_HIT_SS;
869
870 if (p->ainsn.emulate_op) {
871 p->ainsn.emulate_op(p, regs);
872 kprobe_post_process(cur: p, regs, kcb);
873 return;
874 }
875
876 /* Disable interrupt, and set ip register on trampoline */
877 regs->flags &= ~X86_EFLAGS_IF;
878 regs->ip = (unsigned long)p->ainsn.insn;
879}
880NOKPROBE_SYMBOL(setup_singlestep);
881
882/*
883 * Called after single-stepping. p->addr is the address of the
884 * instruction whose first byte has been replaced by the "int3"
885 * instruction. To avoid the SMP problems that can occur when we
886 * temporarily put back the original opcode to single-step, we
887 * single-stepped a copy of the instruction. The address of this
888 * copy is p->ainsn.insn. We also doesn't use trap, but "int3" again
889 * right after the copied instruction.
890 * Different from the trap single-step, "int3" single-step can not
891 * handle the instruction which changes the ip register, e.g. jmp,
892 * call, conditional jmp, and the instructions which changes the IF
893 * flags because interrupt must be disabled around the single-stepping.
894 * Such instructions are software emulated, but others are single-stepped
895 * using "int3".
896 *
897 * When the 2nd "int3" handled, the regs->ip and regs->flags needs to
898 * be adjusted, so that we can resume execution on correct code.
899 */
900static void resume_singlestep(struct kprobe *p, struct pt_regs *regs,
901 struct kprobe_ctlblk *kcb)
902{
903 unsigned long copy_ip = (unsigned long)p->ainsn.insn;
904 unsigned long orig_ip = (unsigned long)p->addr;
905
906 /* Restore saved interrupt flag and ip register */
907 regs->flags |= kcb->kprobe_saved_flags;
908 /* Note that regs->ip is executed int3 so must be a step back */
909 regs->ip += (orig_ip - copy_ip) - INT3_INSN_SIZE;
910}
911NOKPROBE_SYMBOL(resume_singlestep);
912
913/*
914 * We have reentered the kprobe_handler(), since another probe was hit while
915 * within the handler. We save the original kprobes variables and just single
916 * step on the instruction of the new probe without calling any user handlers.
917 */
918static int reenter_kprobe(struct kprobe *p, struct pt_regs *regs,
919 struct kprobe_ctlblk *kcb)
920{
921 switch (kcb->kprobe_status) {
922 case KPROBE_HIT_SSDONE:
923 case KPROBE_HIT_ACTIVE:
924 case KPROBE_HIT_SS:
925 kprobes_inc_nmissed_count(p);
926 setup_singlestep(p, regs, kcb, reenter: 1);
927 break;
928 case KPROBE_REENTER:
929 /* A probe has been hit in the codepath leading up to, or just
930 * after, single-stepping of a probed instruction. This entire
931 * codepath should strictly reside in .kprobes.text section.
932 * Raise a BUG or we'll continue in an endless reentering loop
933 * and eventually a stack overflow.
934 */
935 pr_err("Unrecoverable kprobe detected.\n");
936 dump_kprobe(kp: p);
937 BUG();
938 default:
939 /* impossible cases */
940 WARN_ON(1);
941 return 0;
942 }
943
944 return 1;
945}
946NOKPROBE_SYMBOL(reenter_kprobe);
947
948static nokprobe_inline int kprobe_is_ss(struct kprobe_ctlblk *kcb)
949{
950 return (kcb->kprobe_status == KPROBE_HIT_SS ||
951 kcb->kprobe_status == KPROBE_REENTER);
952}
953
954/*
955 * Interrupts are disabled on entry as trap3 is an interrupt gate and they
956 * remain disabled throughout this function.
957 */
958int kprobe_int3_handler(struct pt_regs *regs)
959{
960 kprobe_opcode_t *addr;
961 struct kprobe *p;
962 struct kprobe_ctlblk *kcb;
963
964 if (user_mode(regs))
965 return 0;
966
967 addr = (kprobe_opcode_t *)(regs->ip - sizeof(kprobe_opcode_t));
968 /*
969 * We don't want to be preempted for the entire duration of kprobe
970 * processing. Since int3 and debug trap disables irqs and we clear
971 * IF while singlestepping, it must be no preemptible.
972 */
973
974 kcb = get_kprobe_ctlblk();
975 p = get_kprobe(addr);
976
977 if (p) {
978 if (kprobe_running()) {
979 if (reenter_kprobe(p, regs, kcb))
980 return 1;
981 } else {
982 set_current_kprobe(p, regs, kcb);
983 kcb->kprobe_status = KPROBE_HIT_ACTIVE;
984
985 /*
986 * If we have no pre-handler or it returned 0, we
987 * continue with normal processing. If we have a
988 * pre-handler and it returned non-zero, that means
989 * user handler setup registers to exit to another
990 * instruction, we must skip the single stepping.
991 */
992 if (!p->pre_handler || !p->pre_handler(p, regs))
993 setup_singlestep(p, regs, kcb, reenter: 0);
994 else
995 reset_current_kprobe();
996 return 1;
997 }
998 } else if (kprobe_is_ss(kcb)) {
999 p = kprobe_running();
1000 if ((unsigned long)p->ainsn.insn < regs->ip &&
1001 (unsigned long)p->ainsn.insn + MAX_INSN_SIZE > regs->ip) {
1002 /* Most provably this is the second int3 for singlestep */
1003 resume_singlestep(p, regs, kcb);
1004 kprobe_post_process(cur: p, regs, kcb);
1005 return 1;
1006 }
1007 } /* else: not a kprobe fault; let the kernel handle it */
1008
1009 return 0;
1010}
1011NOKPROBE_SYMBOL(kprobe_int3_handler);
1012
1013int kprobe_fault_handler(struct pt_regs *regs, int trapnr)
1014{
1015 struct kprobe *cur = kprobe_running();
1016 struct kprobe_ctlblk *kcb = get_kprobe_ctlblk();
1017
1018 if (unlikely(regs->ip == (unsigned long)cur->ainsn.insn)) {
1019 /* This must happen on single-stepping */
1020 WARN_ON(kcb->kprobe_status != KPROBE_HIT_SS &&
1021 kcb->kprobe_status != KPROBE_REENTER);
1022 /*
1023 * We are here because the instruction being single
1024 * stepped caused a page fault. We reset the current
1025 * kprobe and the ip points back to the probe address
1026 * and allow the page fault handler to continue as a
1027 * normal page fault.
1028 */
1029 regs->ip = (unsigned long)cur->addr;
1030
1031 /*
1032 * If the IF flag was set before the kprobe hit,
1033 * don't touch it:
1034 */
1035 regs->flags |= kcb->kprobe_old_flags;
1036
1037 if (kcb->kprobe_status == KPROBE_REENTER)
1038 restore_previous_kprobe(kcb);
1039 else
1040 reset_current_kprobe();
1041 }
1042
1043 return 0;
1044}
1045NOKPROBE_SYMBOL(kprobe_fault_handler);
1046
1047int __init arch_populate_kprobe_blacklist(void)
1048{
1049 return kprobe_add_area_blacklist(start: (unsigned long)__entry_text_start,
1050 end: (unsigned long)__entry_text_end);
1051}
1052
1053int __init arch_init_kprobes(void)
1054{
1055 return 0;
1056}
1057
1058int arch_trampoline_kprobe(struct kprobe *p)
1059{
1060 return 0;
1061}
1062

source code of linux/arch/x86/kernel/kprobes/core.c