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1da177e4 LT |
1 | /* |
2 | * Kernel Probes (KProbes) | |
3 | * arch/i386/kernel/kprobes.c | |
4 | * | |
5 | * This program is free software; you can redistribute it and/or modify | |
6 | * it under the terms of the GNU General Public License as published by | |
7 | * the Free Software Foundation; either version 2 of the License, or | |
8 | * (at your option) any later version. | |
9 | * | |
10 | * This program is distributed in the hope that it will be useful, | |
11 | * but WITHOUT ANY WARRANTY; without even the implied warranty of | |
12 | * MERCHANTABILITY or FITNESS FOR A PARTICULAR PURPOSE. See the | |
13 | * GNU General Public License for more details. | |
14 | * | |
15 | * You should have received a copy of the GNU General Public License | |
16 | * along with this program; if not, write to the Free Software | |
17 | * Foundation, Inc., 59 Temple Place - Suite 330, Boston, MA 02111-1307, USA. | |
18 | * | |
19 | * Copyright (C) IBM Corporation, 2002, 2004 | |
20 | * | |
21 | * 2002-Oct Created by Vamsi Krishna S <vamsi_krishna@in.ibm.com> Kernel | |
22 | * Probes initial implementation ( includes contributions from | |
23 | * Rusty Russell). | |
24 | * 2004-July Suparna Bhattacharya <suparna@in.ibm.com> added jumper probes | |
25 | * interface to access function arguments. | |
26 | */ | |
27 | ||
28 | #include <linux/config.h> | |
29 | #include <linux/kprobes.h> | |
30 | #include <linux/ptrace.h> | |
31 | #include <linux/spinlock.h> | |
32 | #include <linux/preempt.h> | |
33 | #include <asm/kdebug.h> | |
34 | #include <asm/desc.h> | |
35 | ||
36 | /* kprobe_status settings */ | |
37 | #define KPROBE_HIT_ACTIVE 0x00000001 | |
38 | #define KPROBE_HIT_SS 0x00000002 | |
39 | ||
40 | static struct kprobe *current_kprobe; | |
41 | static unsigned long kprobe_status, kprobe_old_eflags, kprobe_saved_eflags; | |
42 | static struct pt_regs jprobe_saved_regs; | |
43 | static long *jprobe_saved_esp; | |
44 | /* copy of the kernel stack at the probe fire time */ | |
45 | static kprobe_opcode_t jprobes_stack[MAX_STACK_SIZE]; | |
46 | void jprobe_return_end(void); | |
47 | ||
48 | /* | |
49 | * returns non-zero if opcode modifies the interrupt flag. | |
50 | */ | |
51 | static inline int is_IF_modifier(kprobe_opcode_t opcode) | |
52 | { | |
53 | switch (opcode) { | |
54 | case 0xfa: /* cli */ | |
55 | case 0xfb: /* sti */ | |
56 | case 0xcf: /* iret/iretd */ | |
57 | case 0x9d: /* popf/popfd */ | |
58 | return 1; | |
59 | } | |
60 | return 0; | |
61 | } | |
62 | ||
63 | int arch_prepare_kprobe(struct kprobe *p) | |
64 | { | |
65 | return 0; | |
66 | } | |
67 | ||
68 | void arch_copy_kprobe(struct kprobe *p) | |
69 | { | |
70 | memcpy(p->ainsn.insn, p->addr, MAX_INSN_SIZE * sizeof(kprobe_opcode_t)); | |
71 | } | |
72 | ||
73 | void arch_remove_kprobe(struct kprobe *p) | |
74 | { | |
75 | } | |
76 | ||
77 | static inline void disarm_kprobe(struct kprobe *p, struct pt_regs *regs) | |
78 | { | |
79 | *p->addr = p->opcode; | |
80 | regs->eip = (unsigned long)p->addr; | |
81 | } | |
82 | ||
83 | static inline void prepare_singlestep(struct kprobe *p, struct pt_regs *regs) | |
84 | { | |
85 | regs->eflags |= TF_MASK; | |
86 | regs->eflags &= ~IF_MASK; | |
87 | /*single step inline if the instruction is an int3*/ | |
88 | if (p->opcode == BREAKPOINT_INSTRUCTION) | |
89 | regs->eip = (unsigned long)p->addr; | |
90 | else | |
91 | regs->eip = (unsigned long)&p->ainsn.insn; | |
92 | } | |
93 | ||
94 | /* | |
95 | * Interrupts are disabled on entry as trap3 is an interrupt gate and they | |
96 | * remain disabled thorough out this function. | |
97 | */ | |
98 | static int kprobe_handler(struct pt_regs *regs) | |
99 | { | |
100 | struct kprobe *p; | |
101 | int ret = 0; | |
102 | kprobe_opcode_t *addr = NULL; | |
103 | unsigned long *lp; | |
104 | ||
105 | /* We're in an interrupt, but this is clear and BUG()-safe. */ | |
106 | preempt_disable(); | |
107 | /* Check if the application is using LDT entry for its code segment and | |
108 | * calculate the address by reading the base address from the LDT entry. | |
109 | */ | |
110 | if ((regs->xcs & 4) && (current->mm)) { | |
111 | lp = (unsigned long *) ((unsigned long)((regs->xcs >> 3) * 8) | |
112 | + (char *) current->mm->context.ldt); | |
113 | addr = (kprobe_opcode_t *) (get_desc_base(lp) + regs->eip - | |
114 | sizeof(kprobe_opcode_t)); | |
115 | } else { | |
116 | addr = (kprobe_opcode_t *)(regs->eip - sizeof(kprobe_opcode_t)); | |
117 | } | |
118 | /* Check we're not actually recursing */ | |
119 | if (kprobe_running()) { | |
120 | /* We *are* holding lock here, so this is safe. | |
121 | Disarm the probe we just hit, and ignore it. */ | |
122 | p = get_kprobe(addr); | |
123 | if (p) { | |
124 | if (kprobe_status == KPROBE_HIT_SS) { | |
125 | regs->eflags &= ~TF_MASK; | |
126 | regs->eflags |= kprobe_saved_eflags; | |
127 | unlock_kprobes(); | |
128 | goto no_kprobe; | |
129 | } | |
130 | disarm_kprobe(p, regs); | |
131 | ret = 1; | |
132 | } else { | |
133 | p = current_kprobe; | |
134 | if (p->break_handler && p->break_handler(p, regs)) { | |
135 | goto ss_probe; | |
136 | } | |
137 | } | |
138 | /* If it's not ours, can't be delete race, (we hold lock). */ | |
139 | goto no_kprobe; | |
140 | } | |
141 | ||
142 | lock_kprobes(); | |
143 | p = get_kprobe(addr); | |
144 | if (!p) { | |
145 | unlock_kprobes(); | |
146 | if (regs->eflags & VM_MASK) { | |
147 | /* We are in virtual-8086 mode. Return 0 */ | |
148 | goto no_kprobe; | |
149 | } | |
150 | ||
151 | if (*addr != BREAKPOINT_INSTRUCTION) { | |
152 | /* | |
153 | * The breakpoint instruction was removed right | |
154 | * after we hit it. Another cpu has removed | |
155 | * either a probepoint or a debugger breakpoint | |
156 | * at this address. In either case, no further | |
157 | * handling of this interrupt is appropriate. | |
158 | */ | |
159 | ret = 1; | |
160 | } | |
161 | /* Not one of ours: let kernel handle it */ | |
162 | goto no_kprobe; | |
163 | } | |
164 | ||
165 | kprobe_status = KPROBE_HIT_ACTIVE; | |
166 | current_kprobe = p; | |
167 | kprobe_saved_eflags = kprobe_old_eflags | |
168 | = (regs->eflags & (TF_MASK | IF_MASK)); | |
169 | if (is_IF_modifier(p->opcode)) | |
170 | kprobe_saved_eflags &= ~IF_MASK; | |
171 | ||
172 | if (p->pre_handler && p->pre_handler(p, regs)) | |
173 | /* handler has already set things up, so skip ss setup */ | |
174 | return 1; | |
175 | ||
176 | ss_probe: | |
177 | prepare_singlestep(p, regs); | |
178 | kprobe_status = KPROBE_HIT_SS; | |
179 | return 1; | |
180 | ||
181 | no_kprobe: | |
182 | preempt_enable_no_resched(); | |
183 | return ret; | |
184 | } | |
185 | ||
186 | /* | |
187 | * Called after single-stepping. p->addr is the address of the | |
188 | * instruction whose first byte has been replaced by the "int 3" | |
189 | * instruction. To avoid the SMP problems that can occur when we | |
190 | * temporarily put back the original opcode to single-step, we | |
191 | * single-stepped a copy of the instruction. The address of this | |
192 | * copy is p->ainsn.insn. | |
193 | * | |
194 | * This function prepares to return from the post-single-step | |
195 | * interrupt. We have to fix up the stack as follows: | |
196 | * | |
197 | * 0) Except in the case of absolute or indirect jump or call instructions, | |
198 | * the new eip is relative to the copied instruction. We need to make | |
199 | * it relative to the original instruction. | |
200 | * | |
201 | * 1) If the single-stepped instruction was pushfl, then the TF and IF | |
202 | * flags are set in the just-pushed eflags, and may need to be cleared. | |
203 | * | |
204 | * 2) If the single-stepped instruction was a call, the return address | |
205 | * that is atop the stack is the address following the copied instruction. | |
206 | * We need to make it the address following the original instruction. | |
207 | */ | |
208 | static void resume_execution(struct kprobe *p, struct pt_regs *regs) | |
209 | { | |
210 | unsigned long *tos = (unsigned long *)®s->esp; | |
211 | unsigned long next_eip = 0; | |
212 | unsigned long copy_eip = (unsigned long)&p->ainsn.insn; | |
213 | unsigned long orig_eip = (unsigned long)p->addr; | |
214 | ||
215 | switch (p->ainsn.insn[0]) { | |
216 | case 0x9c: /* pushfl */ | |
217 | *tos &= ~(TF_MASK | IF_MASK); | |
218 | *tos |= kprobe_old_eflags; | |
219 | break; | |
220 | case 0xe8: /* call relative - Fix return addr */ | |
221 | *tos = orig_eip + (*tos - copy_eip); | |
222 | break; | |
223 | case 0xff: | |
224 | if ((p->ainsn.insn[1] & 0x30) == 0x10) { | |
225 | /* call absolute, indirect */ | |
226 | /* Fix return addr; eip is correct. */ | |
227 | next_eip = regs->eip; | |
228 | *tos = orig_eip + (*tos - copy_eip); | |
229 | } else if (((p->ainsn.insn[1] & 0x31) == 0x20) || /* jmp near, absolute indirect */ | |
230 | ((p->ainsn.insn[1] & 0x31) == 0x21)) { /* jmp far, absolute indirect */ | |
231 | /* eip is correct. */ | |
232 | next_eip = regs->eip; | |
233 | } | |
234 | break; | |
235 | case 0xea: /* jmp absolute -- eip is correct */ | |
236 | next_eip = regs->eip; | |
237 | break; | |
238 | default: | |
239 | break; | |
240 | } | |
241 | ||
242 | regs->eflags &= ~TF_MASK; | |
243 | if (next_eip) { | |
244 | regs->eip = next_eip; | |
245 | } else { | |
246 | regs->eip = orig_eip + (regs->eip - copy_eip); | |
247 | } | |
248 | } | |
249 | ||
250 | /* | |
251 | * Interrupts are disabled on entry as trap1 is an interrupt gate and they | |
252 | * remain disabled thoroughout this function. And we hold kprobe lock. | |
253 | */ | |
254 | static inline int post_kprobe_handler(struct pt_regs *regs) | |
255 | { | |
256 | if (!kprobe_running()) | |
257 | return 0; | |
258 | ||
259 | if (current_kprobe->post_handler) | |
260 | current_kprobe->post_handler(current_kprobe, regs, 0); | |
261 | ||
262 | resume_execution(current_kprobe, regs); | |
263 | regs->eflags |= kprobe_saved_eflags; | |
264 | ||
265 | unlock_kprobes(); | |
266 | preempt_enable_no_resched(); | |
267 | ||
268 | /* | |
269 | * if somebody else is singlestepping across a probe point, eflags | |
270 | * will have TF set, in which case, continue the remaining processing | |
271 | * of do_debug, as if this is not a probe hit. | |
272 | */ | |
273 | if (regs->eflags & TF_MASK) | |
274 | return 0; | |
275 | ||
276 | return 1; | |
277 | } | |
278 | ||
279 | /* Interrupts disabled, kprobe_lock held. */ | |
280 | static inline int kprobe_fault_handler(struct pt_regs *regs, int trapnr) | |
281 | { | |
282 | if (current_kprobe->fault_handler | |
283 | && current_kprobe->fault_handler(current_kprobe, regs, trapnr)) | |
284 | return 1; | |
285 | ||
286 | if (kprobe_status & KPROBE_HIT_SS) { | |
287 | resume_execution(current_kprobe, regs); | |
288 | regs->eflags |= kprobe_old_eflags; | |
289 | ||
290 | unlock_kprobes(); | |
291 | preempt_enable_no_resched(); | |
292 | } | |
293 | return 0; | |
294 | } | |
295 | ||
296 | /* | |
297 | * Wrapper routine to for handling exceptions. | |
298 | */ | |
299 | int kprobe_exceptions_notify(struct notifier_block *self, unsigned long val, | |
300 | void *data) | |
301 | { | |
302 | struct die_args *args = (struct die_args *)data; | |
303 | switch (val) { | |
304 | case DIE_INT3: | |
305 | if (kprobe_handler(args->regs)) | |
306 | return NOTIFY_STOP; | |
307 | break; | |
308 | case DIE_DEBUG: | |
309 | if (post_kprobe_handler(args->regs)) | |
310 | return NOTIFY_STOP; | |
311 | break; | |
312 | case DIE_GPF: | |
313 | if (kprobe_running() && | |
314 | kprobe_fault_handler(args->regs, args->trapnr)) | |
315 | return NOTIFY_STOP; | |
316 | break; | |
317 | case DIE_PAGE_FAULT: | |
318 | if (kprobe_running() && | |
319 | kprobe_fault_handler(args->regs, args->trapnr)) | |
320 | return NOTIFY_STOP; | |
321 | break; | |
322 | default: | |
323 | break; | |
324 | } | |
325 | return NOTIFY_DONE; | |
326 | } | |
327 | ||
328 | int setjmp_pre_handler(struct kprobe *p, struct pt_regs *regs) | |
329 | { | |
330 | struct jprobe *jp = container_of(p, struct jprobe, kp); | |
331 | unsigned long addr; | |
332 | ||
333 | jprobe_saved_regs = *regs; | |
334 | jprobe_saved_esp = ®s->esp; | |
335 | addr = (unsigned long)jprobe_saved_esp; | |
336 | ||
337 | /* | |
338 | * TBD: As Linus pointed out, gcc assumes that the callee | |
339 | * owns the argument space and could overwrite it, e.g. | |
340 | * tailcall optimization. So, to be absolutely safe | |
341 | * we also save and restore enough stack bytes to cover | |
342 | * the argument area. | |
343 | */ | |
344 | memcpy(jprobes_stack, (kprobe_opcode_t *) addr, MIN_STACK_SIZE(addr)); | |
345 | regs->eflags &= ~IF_MASK; | |
346 | regs->eip = (unsigned long)(jp->entry); | |
347 | return 1; | |
348 | } | |
349 | ||
350 | void jprobe_return(void) | |
351 | { | |
352 | preempt_enable_no_resched(); | |
353 | asm volatile (" xchgl %%ebx,%%esp \n" | |
354 | " int3 \n" | |
355 | " .globl jprobe_return_end \n" | |
356 | " jprobe_return_end: \n" | |
357 | " nop \n"::"b" | |
358 | (jprobe_saved_esp):"memory"); | |
359 | } | |
360 | ||
361 | int longjmp_break_handler(struct kprobe *p, struct pt_regs *regs) | |
362 | { | |
363 | u8 *addr = (u8 *) (regs->eip - 1); | |
364 | unsigned long stack_addr = (unsigned long)jprobe_saved_esp; | |
365 | struct jprobe *jp = container_of(p, struct jprobe, kp); | |
366 | ||
367 | if ((addr > (u8 *) jprobe_return) && (addr < (u8 *) jprobe_return_end)) { | |
368 | if (®s->esp != jprobe_saved_esp) { | |
369 | struct pt_regs *saved_regs = | |
370 | container_of(jprobe_saved_esp, struct pt_regs, esp); | |
371 | printk("current esp %p does not match saved esp %p\n", | |
372 | ®s->esp, jprobe_saved_esp); | |
373 | printk("Saved registers for jprobe %p\n", jp); | |
374 | show_registers(saved_regs); | |
375 | printk("Current registers\n"); | |
376 | show_registers(regs); | |
377 | BUG(); | |
378 | } | |
379 | *regs = jprobe_saved_regs; | |
380 | memcpy((kprobe_opcode_t *) stack_addr, jprobes_stack, | |
381 | MIN_STACK_SIZE(stack_addr)); | |
382 | return 1; | |
383 | } | |
384 | return 0; | |
385 | } |