Merge branch 'x86-pti-for-linus' of git://git.kernel.org/pub/scm/linux/kernel/git...
[muen/linux.git] / arch / x86 / kernel / kprobes / opt.c
1 /*
2  *  Kernel Probes Jump Optimization (Optprobes)
3  *
4  * This program is free software; you can redistribute it and/or modify
5  * it under the terms of the GNU General Public License as published by
6  * the Free Software Foundation; either version 2 of the License, or
7  * (at your option) any later version.
8  *
9  * This program is distributed in the hope that it will be useful,
10  * but WITHOUT ANY WARRANTY; without even the implied warranty of
11  * MERCHANTABILITY or FITNESS FOR A PARTICULAR PURPOSE.  See the
12  * GNU General Public License for more details.
13  *
14  * You should have received a copy of the GNU General Public License
15  * along with this program; if not, write to the Free Software
16  * Foundation, Inc., 59 Temple Place - Suite 330, Boston, MA 02111-1307, USA.
17  *
18  * Copyright (C) IBM Corporation, 2002, 2004
19  * Copyright (C) Hitachi Ltd., 2012
20  */
21 #include <linux/kprobes.h>
22 #include <linux/ptrace.h>
23 #include <linux/string.h>
24 #include <linux/slab.h>
25 #include <linux/hardirq.h>
26 #include <linux/preempt.h>
27 #include <linux/extable.h>
28 #include <linux/kdebug.h>
29 #include <linux/kallsyms.h>
30 #include <linux/ftrace.h>
31 #include <linux/frame.h>
32
33 #include <asm/text-patching.h>
34 #include <asm/cacheflush.h>
35 #include <asm/desc.h>
36 #include <asm/pgtable.h>
37 #include <linux/uaccess.h>
38 #include <asm/alternative.h>
39 #include <asm/insn.h>
40 #include <asm/debugreg.h>
41 #include <asm/set_memory.h>
42 #include <asm/sections.h>
43 #include <asm/nospec-branch.h>
44
45 #include "common.h"
46
47 unsigned long __recover_optprobed_insn(kprobe_opcode_t *buf, unsigned long addr)
48 {
49         struct optimized_kprobe *op;
50         struct kprobe *kp;
51         long offs;
52         int i;
53
54         for (i = 0; i < RELATIVEJUMP_SIZE; i++) {
55                 kp = get_kprobe((void *)addr - i);
56                 /* This function only handles jump-optimized kprobe */
57                 if (kp && kprobe_optimized(kp)) {
58                         op = container_of(kp, struct optimized_kprobe, kp);
59                         /* If op->list is not empty, op is under optimizing */
60                         if (list_empty(&op->list))
61                                 goto found;
62                 }
63         }
64
65         return addr;
66 found:
67         /*
68          * If the kprobe can be optimized, original bytes which can be
69          * overwritten by jump destination address. In this case, original
70          * bytes must be recovered from op->optinsn.copied_insn buffer.
71          */
72         if (probe_kernel_read(buf, (void *)addr,
73                 MAX_INSN_SIZE * sizeof(kprobe_opcode_t)))
74                 return 0UL;
75
76         if (addr == (unsigned long)kp->addr) {
77                 buf[0] = kp->opcode;
78                 memcpy(buf + 1, op->optinsn.copied_insn, RELATIVE_ADDR_SIZE);
79         } else {
80                 offs = addr - (unsigned long)kp->addr - 1;
81                 memcpy(buf, op->optinsn.copied_insn + offs, RELATIVE_ADDR_SIZE - offs);
82         }
83
84         return (unsigned long)buf;
85 }
86
87 /* Insert a move instruction which sets a pointer to eax/rdi (1st arg). */
88 static void synthesize_set_arg1(kprobe_opcode_t *addr, unsigned long val)
89 {
90 #ifdef CONFIG_X86_64
91         *addr++ = 0x48;
92         *addr++ = 0xbf;
93 #else
94         *addr++ = 0xb8;
95 #endif
96         *(unsigned long *)addr = val;
97 }
98
99 asm (
100                         "optprobe_template_func:\n"
101                         ".global optprobe_template_entry\n"
102                         "optprobe_template_entry:\n"
103 #ifdef CONFIG_X86_64
104                         /* We don't bother saving the ss register */
105                         "       pushq %rsp\n"
106                         "       pushfq\n"
107                         SAVE_REGS_STRING
108                         "       movq %rsp, %rsi\n"
109                         ".global optprobe_template_val\n"
110                         "optprobe_template_val:\n"
111                         ASM_NOP5
112                         ASM_NOP5
113                         ".global optprobe_template_call\n"
114                         "optprobe_template_call:\n"
115                         ASM_NOP5
116                         /* Move flags to rsp */
117                         "       movq 144(%rsp), %rdx\n"
118                         "       movq %rdx, 152(%rsp)\n"
119                         RESTORE_REGS_STRING
120                         /* Skip flags entry */
121                         "       addq $8, %rsp\n"
122                         "       popfq\n"
123 #else /* CONFIG_X86_32 */
124                         "       pushf\n"
125                         SAVE_REGS_STRING
126                         "       movl %esp, %edx\n"
127                         ".global optprobe_template_val\n"
128                         "optprobe_template_val:\n"
129                         ASM_NOP5
130                         ".global optprobe_template_call\n"
131                         "optprobe_template_call:\n"
132                         ASM_NOP5
133                         RESTORE_REGS_STRING
134                         "       addl $4, %esp\n"        /* skip cs */
135                         "       popf\n"
136 #endif
137                         ".global optprobe_template_end\n"
138                         "optprobe_template_end:\n"
139                         ".type optprobe_template_func, @function\n"
140                         ".size optprobe_template_func, .-optprobe_template_func\n");
141
142 void optprobe_template_func(void);
143 STACK_FRAME_NON_STANDARD(optprobe_template_func);
144
145 #define TMPL_MOVE_IDX \
146         ((long)optprobe_template_val - (long)optprobe_template_entry)
147 #define TMPL_CALL_IDX \
148         ((long)optprobe_template_call - (long)optprobe_template_entry)
149 #define TMPL_END_IDX \
150         ((long)optprobe_template_end - (long)optprobe_template_entry)
151
152 #define INT3_SIZE sizeof(kprobe_opcode_t)
153
154 /* Optimized kprobe call back function: called from optinsn */
155 static void
156 optimized_callback(struct optimized_kprobe *op, struct pt_regs *regs)
157 {
158         /* This is possible if op is under delayed unoptimizing */
159         if (kprobe_disabled(&op->kp))
160                 return;
161
162         preempt_disable();
163         if (kprobe_running()) {
164                 kprobes_inc_nmissed_count(&op->kp);
165         } else {
166                 struct kprobe_ctlblk *kcb = get_kprobe_ctlblk();
167                 /* Save skipped registers */
168 #ifdef CONFIG_X86_64
169                 regs->cs = __KERNEL_CS;
170 #else
171                 regs->cs = __KERNEL_CS | get_kernel_rpl();
172                 regs->gs = 0;
173 #endif
174                 regs->ip = (unsigned long)op->kp.addr + INT3_SIZE;
175                 regs->orig_ax = ~0UL;
176
177                 __this_cpu_write(current_kprobe, &op->kp);
178                 kcb->kprobe_status = KPROBE_HIT_ACTIVE;
179                 opt_pre_handler(&op->kp, regs);
180                 __this_cpu_write(current_kprobe, NULL);
181         }
182         preempt_enable_no_resched();
183 }
184 NOKPROBE_SYMBOL(optimized_callback);
185
186 static int copy_optimized_instructions(u8 *dest, u8 *src, u8 *real)
187 {
188         struct insn insn;
189         int len = 0, ret;
190
191         while (len < RELATIVEJUMP_SIZE) {
192                 ret = __copy_instruction(dest + len, src + len, real, &insn);
193                 if (!ret || !can_boost(&insn, src + len))
194                         return -EINVAL;
195                 len += ret;
196         }
197         /* Check whether the address range is reserved */
198         if (ftrace_text_reserved(src, src + len - 1) ||
199             alternatives_text_reserved(src, src + len - 1) ||
200             jump_label_text_reserved(src, src + len - 1))
201                 return -EBUSY;
202
203         return len;
204 }
205
206 /* Check whether insn is indirect jump */
207 static int __insn_is_indirect_jump(struct insn *insn)
208 {
209         return ((insn->opcode.bytes[0] == 0xff &&
210                 (X86_MODRM_REG(insn->modrm.value) & 6) == 4) || /* Jump */
211                 insn->opcode.bytes[0] == 0xea); /* Segment based jump */
212 }
213
214 /* Check whether insn jumps into specified address range */
215 static int insn_jump_into_range(struct insn *insn, unsigned long start, int len)
216 {
217         unsigned long target = 0;
218
219         switch (insn->opcode.bytes[0]) {
220         case 0xe0:      /* loopne */
221         case 0xe1:      /* loope */
222         case 0xe2:      /* loop */
223         case 0xe3:      /* jcxz */
224         case 0xe9:      /* near relative jump */
225         case 0xeb:      /* short relative jump */
226                 break;
227         case 0x0f:
228                 if ((insn->opcode.bytes[1] & 0xf0) == 0x80) /* jcc near */
229                         break;
230                 return 0;
231         default:
232                 if ((insn->opcode.bytes[0] & 0xf0) == 0x70) /* jcc short */
233                         break;
234                 return 0;
235         }
236         target = (unsigned long)insn->next_byte + insn->immediate.value;
237
238         return (start <= target && target <= start + len);
239 }
240
241 static int insn_is_indirect_jump(struct insn *insn)
242 {
243         int ret = __insn_is_indirect_jump(insn);
244
245 #ifdef CONFIG_RETPOLINE
246         /*
247          * Jump to x86_indirect_thunk_* is treated as an indirect jump.
248          * Note that even with CONFIG_RETPOLINE=y, the kernel compiled with
249          * older gcc may use indirect jump. So we add this check instead of
250          * replace indirect-jump check.
251          */
252         if (!ret)
253                 ret = insn_jump_into_range(insn,
254                                 (unsigned long)__indirect_thunk_start,
255                                 (unsigned long)__indirect_thunk_end -
256                                 (unsigned long)__indirect_thunk_start);
257 #endif
258         return ret;
259 }
260
261 /* Decode whole function to ensure any instructions don't jump into target */
262 static int can_optimize(unsigned long paddr)
263 {
264         unsigned long addr, size = 0, offset = 0;
265         struct insn insn;
266         kprobe_opcode_t buf[MAX_INSN_SIZE];
267
268         /* Lookup symbol including addr */
269         if (!kallsyms_lookup_size_offset(paddr, &size, &offset))
270                 return 0;
271
272         /*
273          * Do not optimize in the entry code due to the unstable
274          * stack handling and registers setup.
275          */
276         if (((paddr >= (unsigned long)__entry_text_start) &&
277              (paddr <  (unsigned long)__entry_text_end)) ||
278             ((paddr >= (unsigned long)__irqentry_text_start) &&
279              (paddr <  (unsigned long)__irqentry_text_end)))
280                 return 0;
281
282         /* Check there is enough space for a relative jump. */
283         if (size - offset < RELATIVEJUMP_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                 if (search_exception_tables(addr))
291                         /*
292                          * Since some fixup code will jumps into this function,
293                          * we can't optimize kprobe in this function.
294                          */
295                         return 0;
296                 recovered_insn = recover_probed_instruction(buf, addr);
297                 if (!recovered_insn)
298                         return 0;
299                 kernel_insn_init(&insn, (void *)recovered_insn, MAX_INSN_SIZE);
300                 insn_get_length(&insn);
301                 /* Another subsystem puts a breakpoint */
302                 if (insn.opcode.bytes[0] == BREAKPOINT_INSTRUCTION)
303                         return 0;
304                 /* Recover address */
305                 insn.kaddr = (void *)addr;
306                 insn.next_byte = (void *)(addr + insn.length);
307                 /* Check any instructions don't jump into target */
308                 if (insn_is_indirect_jump(&insn) ||
309                     insn_jump_into_range(&insn, paddr + INT3_SIZE,
310                                          RELATIVE_ADDR_SIZE))
311                         return 0;
312                 addr += insn.length;
313         }
314
315         return 1;
316 }
317
318 /* Check optimized_kprobe can actually be optimized. */
319 int arch_check_optimized_kprobe(struct optimized_kprobe *op)
320 {
321         int i;
322         struct kprobe *p;
323
324         for (i = 1; i < op->optinsn.size; i++) {
325                 p = get_kprobe(op->kp.addr + i);
326                 if (p && !kprobe_disabled(p))
327                         return -EEXIST;
328         }
329
330         return 0;
331 }
332
333 /* Check the addr is within the optimized instructions. */
334 int arch_within_optimized_kprobe(struct optimized_kprobe *op,
335                                  unsigned long addr)
336 {
337         return ((unsigned long)op->kp.addr <= addr &&
338                 (unsigned long)op->kp.addr + op->optinsn.size > addr);
339 }
340
341 /* Free optimized instruction slot */
342 static
343 void __arch_remove_optimized_kprobe(struct optimized_kprobe *op, int dirty)
344 {
345         if (op->optinsn.insn) {
346                 free_optinsn_slot(op->optinsn.insn, dirty);
347                 op->optinsn.insn = NULL;
348                 op->optinsn.size = 0;
349         }
350 }
351
352 void arch_remove_optimized_kprobe(struct optimized_kprobe *op)
353 {
354         __arch_remove_optimized_kprobe(op, 1);
355 }
356
357 /*
358  * Copy replacing target instructions
359  * Target instructions MUST be relocatable (checked inside)
360  * This is called when new aggr(opt)probe is allocated or reused.
361  */
362 int arch_prepare_optimized_kprobe(struct optimized_kprobe *op,
363                                   struct kprobe *__unused)
364 {
365         u8 *buf = NULL, *slot;
366         int ret, len;
367         long rel;
368
369         if (!can_optimize((unsigned long)op->kp.addr))
370                 return -EILSEQ;
371
372         buf = kzalloc(MAX_OPTINSN_SIZE, GFP_KERNEL);
373         if (!buf)
374                 return -ENOMEM;
375
376         op->optinsn.insn = slot = get_optinsn_slot();
377         if (!slot) {
378                 ret = -ENOMEM;
379                 goto out;
380         }
381
382         /*
383          * Verify if the address gap is in 2GB range, because this uses
384          * a relative jump.
385          */
386         rel = (long)slot - (long)op->kp.addr + RELATIVEJUMP_SIZE;
387         if (abs(rel) > 0x7fffffff) {
388                 ret = -ERANGE;
389                 goto err;
390         }
391
392         /* Copy arch-dep-instance from template */
393         memcpy(buf, optprobe_template_entry, TMPL_END_IDX);
394
395         /* Copy instructions into the out-of-line buffer */
396         ret = copy_optimized_instructions(buf + TMPL_END_IDX, op->kp.addr,
397                                           slot + TMPL_END_IDX);
398         if (ret < 0)
399                 goto err;
400         op->optinsn.size = ret;
401         len = TMPL_END_IDX + op->optinsn.size;
402
403         /* Set probe information */
404         synthesize_set_arg1(buf + TMPL_MOVE_IDX, (unsigned long)op);
405
406         /* Set probe function call */
407         synthesize_relcall(buf + TMPL_CALL_IDX,
408                            slot + TMPL_CALL_IDX, optimized_callback);
409
410         /* Set returning jmp instruction at the tail of out-of-line buffer */
411         synthesize_reljump(buf + len, slot + len,
412                            (u8 *)op->kp.addr + op->optinsn.size);
413         len += RELATIVEJUMP_SIZE;
414
415         /* We have to use text_poke for instuction buffer because it is RO */
416         text_poke(slot, buf, len);
417         ret = 0;
418 out:
419         kfree(buf);
420         return ret;
421
422 err:
423         __arch_remove_optimized_kprobe(op, 0);
424         goto out;
425 }
426
427 /*
428  * Replace breakpoints (int3) with relative jumps.
429  * Caller must call with locking kprobe_mutex and text_mutex.
430  */
431 void arch_optimize_kprobes(struct list_head *oplist)
432 {
433         struct optimized_kprobe *op, *tmp;
434         u8 insn_buf[RELATIVEJUMP_SIZE];
435
436         list_for_each_entry_safe(op, tmp, oplist, list) {
437                 s32 rel = (s32)((long)op->optinsn.insn -
438                         ((long)op->kp.addr + RELATIVEJUMP_SIZE));
439
440                 WARN_ON(kprobe_disabled(&op->kp));
441
442                 /* Backup instructions which will be replaced by jump address */
443                 memcpy(op->optinsn.copied_insn, op->kp.addr + INT3_SIZE,
444                        RELATIVE_ADDR_SIZE);
445
446                 insn_buf[0] = RELATIVEJUMP_OPCODE;
447                 *(s32 *)(&insn_buf[1]) = rel;
448
449                 text_poke_bp(op->kp.addr, insn_buf, RELATIVEJUMP_SIZE,
450                              op->optinsn.insn);
451
452                 list_del_init(&op->list);
453         }
454 }
455
456 /* Replace a relative jump with a breakpoint (int3).  */
457 void arch_unoptimize_kprobe(struct optimized_kprobe *op)
458 {
459         u8 insn_buf[RELATIVEJUMP_SIZE];
460
461         /* Set int3 to first byte for kprobes */
462         insn_buf[0] = BREAKPOINT_INSTRUCTION;
463         memcpy(insn_buf + 1, op->optinsn.copied_insn, RELATIVE_ADDR_SIZE);
464         text_poke_bp(op->kp.addr, insn_buf, RELATIVEJUMP_SIZE,
465                      op->optinsn.insn);
466 }
467
468 /*
469  * Recover original instructions and breakpoints from relative jumps.
470  * Caller must call with locking kprobe_mutex.
471  */
472 extern void arch_unoptimize_kprobes(struct list_head *oplist,
473                                     struct list_head *done_list)
474 {
475         struct optimized_kprobe *op, *tmp;
476
477         list_for_each_entry_safe(op, tmp, oplist, list) {
478                 arch_unoptimize_kprobe(op);
479                 list_move(&op->list, done_list);
480         }
481 }
482
483 int setup_detour_execution(struct kprobe *p, struct pt_regs *regs, int reenter)
484 {
485         struct optimized_kprobe *op;
486
487         if (p->flags & KPROBE_FLAG_OPTIMIZED) {
488                 /* This kprobe is really able to run optimized path. */
489                 op = container_of(p, struct optimized_kprobe, kp);
490                 /* Detour through copied instructions */
491                 regs->ip = (unsigned long)op->optinsn.insn + TMPL_END_IDX;
492                 if (!reenter)
493                         reset_current_kprobe();
494                 preempt_enable_no_resched();
495                 return 1;
496         }
497         return 0;
498 }
499 NOKPROBE_SYMBOL(setup_detour_execution);