1 /*
2 * This program is free software; you can redistribute it and/or modify
3 * it under the terms of the GNU General Public License as published by
4 * the Free Software Foundation; either version 2 of the License, or
5 * (at your option) any later version.
6 *
7 * This program is distributed in the hope that it will be useful,
8 * but WITHOUT ANY WARRANTY; without even the implied warranty of
9 * MERCHANTABILITY or FITNESS FOR A PARTICULAR PURPOSE. See the
10 * GNU General Public License for more details.
11 *
12 * You should have received a copy of the GNU General Public License
13 * along with this program; if not, write to the Free Software
14 * Foundation, Inc., 59 Temple Place - Suite 330, Boston, MA 02111-1307, USA.
15 *
16 * Copyright (C) 2007 Alan Stern
17 * Copyright (C) 2009 IBM Corporation
18 * Copyright (C) 2009 Frederic Weisbecker <fweisbec@gmail.com>
19 *
20 * Authors: Alan Stern <stern@rowland.harvard.edu>
21 * K.Prasad <prasad@linux.vnet.ibm.com>
22 * Frederic Weisbecker <fweisbec@gmail.com>
23 */
24
25 /*
26 * HW_breakpoint: a unified kernel/user-space hardware breakpoint facility,
27 * using the CPU's debug registers.
28 */
29
30 #include <linux/perf_event.h>
31 #include <linux/hw_breakpoint.h>
32 #include <linux/irqflags.h>
33 #include <linux/notifier.h>
34 #include <linux/kallsyms.h>
35 #include <linux/kprobes.h>
36 #include <linux/percpu.h>
37 #include <linux/kdebug.h>
38 #include <linux/kernel.h>
39 #include <linux/module.h>
40 #include <linux/sched.h>
41 #include <linux/init.h>
42 #include <linux/smp.h>
43
44 #include <asm/hw_breakpoint.h>
45 #include <asm/processor.h>
46 #include <asm/debugreg.h>
47
48 /* Per cpu debug control register value */
49 DEFINE_PER_CPU(unsigned long, cpu_dr7);
50 EXPORT_PER_CPU_SYMBOL(cpu_dr7);
51
52 /* Per cpu debug address registers values */
53 static DEFINE_PER_CPU(unsigned long, cpu_debugreg[HBP_NUM]);
54
55 /*
56 * Stores the breakpoints currently in use on each breakpoint address
57 * register for each cpus
58 */
59 static DEFINE_PER_CPU(struct perf_event *, bp_per_reg[HBP_NUM]);
60
61
62 static inline unsigned long
__encode_dr7(int drnum,unsigned int len,unsigned int type)63 __encode_dr7(int drnum, unsigned int len, unsigned int type)
64 {
65 unsigned long bp_info;
66
67 bp_info = (len | type) & 0xf;
68 bp_info <<= (DR_CONTROL_SHIFT + drnum * DR_CONTROL_SIZE);
69 bp_info |= (DR_GLOBAL_ENABLE << (drnum * DR_ENABLE_SIZE));
70
71 return bp_info;
72 }
73
74 /*
75 * Encode the length, type, Exact, and Enable bits for a particular breakpoint
76 * as stored in debug register 7.
77 */
encode_dr7(int drnum,unsigned int len,unsigned int type)78 unsigned long encode_dr7(int drnum, unsigned int len, unsigned int type)
79 {
80 return __encode_dr7(drnum, len, type) | DR_GLOBAL_SLOWDOWN;
81 }
82
83 /*
84 * Decode the length and type bits for a particular breakpoint as
85 * stored in debug register 7. Return the "enabled" status.
86 */
decode_dr7(unsigned long dr7,int bpnum,unsigned * len,unsigned * type)87 int decode_dr7(unsigned long dr7, int bpnum, unsigned *len, unsigned *type)
88 {
89 int bp_info = dr7 >> (DR_CONTROL_SHIFT + bpnum * DR_CONTROL_SIZE);
90
91 *len = (bp_info & 0xc) | 0x40;
92 *type = (bp_info & 0x3) | 0x80;
93
94 return (dr7 >> (bpnum * DR_ENABLE_SIZE)) & 0x3;
95 }
96
97 /*
98 * Install a perf counter breakpoint.
99 *
100 * We seek a free debug address register and use it for this
101 * breakpoint. Eventually we enable it in the debug control register.
102 *
103 * Atomic: we hold the counter->ctx->lock and we only handle variables
104 * and registers local to this cpu.
105 */
arch_install_hw_breakpoint(struct perf_event * bp)106 int arch_install_hw_breakpoint(struct perf_event *bp)
107 {
108 struct arch_hw_breakpoint *info = counter_arch_bp(bp);
109 unsigned long *dr7;
110 int i;
111
112 for (i = 0; i < HBP_NUM; i++) {
113 struct perf_event **slot = &__get_cpu_var(bp_per_reg[i]);
114
115 if (!*slot) {
116 *slot = bp;
117 break;
118 }
119 }
120
121 if (WARN_ONCE(i == HBP_NUM, "Can't find any breakpoint slot"))
122 return -EBUSY;
123
124 set_debugreg(info->address, i);
125 __this_cpu_write(cpu_debugreg[i], info->address);
126
127 dr7 = &__get_cpu_var(cpu_dr7);
128 *dr7 |= encode_dr7(i, info->len, info->type);
129
130 set_debugreg(*dr7, 7);
131
132 return 0;
133 }
134
135 /*
136 * Uninstall the breakpoint contained in the given counter.
137 *
138 * First we search the debug address register it uses and then we disable
139 * it.
140 *
141 * Atomic: we hold the counter->ctx->lock and we only handle variables
142 * and registers local to this cpu.
143 */
arch_uninstall_hw_breakpoint(struct perf_event * bp)144 void arch_uninstall_hw_breakpoint(struct perf_event *bp)
145 {
146 struct arch_hw_breakpoint *info = counter_arch_bp(bp);
147 unsigned long *dr7;
148 int i;
149
150 for (i = 0; i < HBP_NUM; i++) {
151 struct perf_event **slot = &__get_cpu_var(bp_per_reg[i]);
152
153 if (*slot == bp) {
154 *slot = NULL;
155 break;
156 }
157 }
158
159 if (WARN_ONCE(i == HBP_NUM, "Can't find any breakpoint slot"))
160 return;
161
162 dr7 = &__get_cpu_var(cpu_dr7);
163 *dr7 &= ~__encode_dr7(i, info->len, info->type);
164
165 set_debugreg(*dr7, 7);
166 }
167
get_hbp_len(u8 hbp_len)168 static int get_hbp_len(u8 hbp_len)
169 {
170 unsigned int len_in_bytes = 0;
171
172 switch (hbp_len) {
173 case X86_BREAKPOINT_LEN_1:
174 len_in_bytes = 1;
175 break;
176 case X86_BREAKPOINT_LEN_2:
177 len_in_bytes = 2;
178 break;
179 case X86_BREAKPOINT_LEN_4:
180 len_in_bytes = 4;
181 break;
182 #ifdef CONFIG_X86_64
183 case X86_BREAKPOINT_LEN_8:
184 len_in_bytes = 8;
185 break;
186 #endif
187 }
188 return len_in_bytes;
189 }
190
191 /*
192 * Check for virtual address in kernel space.
193 */
arch_check_bp_in_kernelspace(struct perf_event * bp)194 int arch_check_bp_in_kernelspace(struct perf_event *bp)
195 {
196 unsigned int len;
197 unsigned long va;
198 struct arch_hw_breakpoint *info = counter_arch_bp(bp);
199
200 va = info->address;
201 len = get_hbp_len(info->len);
202
203 return (va >= TASK_SIZE) && ((va + len - 1) >= TASK_SIZE);
204 }
205
arch_bp_generic_fields(int x86_len,int x86_type,int * gen_len,int * gen_type)206 int arch_bp_generic_fields(int x86_len, int x86_type,
207 int *gen_len, int *gen_type)
208 {
209 /* Type */
210 switch (x86_type) {
211 case X86_BREAKPOINT_EXECUTE:
212 if (x86_len != X86_BREAKPOINT_LEN_X)
213 return -EINVAL;
214
215 *gen_type = HW_BREAKPOINT_X;
216 *gen_len = sizeof(long);
217 return 0;
218 case X86_BREAKPOINT_WRITE:
219 *gen_type = HW_BREAKPOINT_W;
220 break;
221 case X86_BREAKPOINT_RW:
222 *gen_type = HW_BREAKPOINT_W | HW_BREAKPOINT_R;
223 break;
224 default:
225 return -EINVAL;
226 }
227
228 /* Len */
229 switch (x86_len) {
230 case X86_BREAKPOINT_LEN_1:
231 *gen_len = HW_BREAKPOINT_LEN_1;
232 break;
233 case X86_BREAKPOINT_LEN_2:
234 *gen_len = HW_BREAKPOINT_LEN_2;
235 break;
236 case X86_BREAKPOINT_LEN_4:
237 *gen_len = HW_BREAKPOINT_LEN_4;
238 break;
239 #ifdef CONFIG_X86_64
240 case X86_BREAKPOINT_LEN_8:
241 *gen_len = HW_BREAKPOINT_LEN_8;
242 break;
243 #endif
244 default:
245 return -EINVAL;
246 }
247
248 return 0;
249 }
250
251
arch_build_bp_info(struct perf_event * bp)252 static int arch_build_bp_info(struct perf_event *bp)
253 {
254 struct arch_hw_breakpoint *info = counter_arch_bp(bp);
255
256 info->address = bp->attr.bp_addr;
257
258 /* Type */
259 switch (bp->attr.bp_type) {
260 case HW_BREAKPOINT_W:
261 info->type = X86_BREAKPOINT_WRITE;
262 break;
263 case HW_BREAKPOINT_W | HW_BREAKPOINT_R:
264 info->type = X86_BREAKPOINT_RW;
265 break;
266 case HW_BREAKPOINT_X:
267 info->type = X86_BREAKPOINT_EXECUTE;
268 /*
269 * x86 inst breakpoints need to have a specific undefined len.
270 * But we still need to check userspace is not trying to setup
271 * an unsupported length, to get a range breakpoint for example.
272 */
273 if (bp->attr.bp_len == sizeof(long)) {
274 info->len = X86_BREAKPOINT_LEN_X;
275 return 0;
276 }
277 default:
278 return -EINVAL;
279 }
280
281 /* Len */
282 switch (bp->attr.bp_len) {
283 case HW_BREAKPOINT_LEN_1:
284 info->len = X86_BREAKPOINT_LEN_1;
285 break;
286 case HW_BREAKPOINT_LEN_2:
287 info->len = X86_BREAKPOINT_LEN_2;
288 break;
289 case HW_BREAKPOINT_LEN_4:
290 info->len = X86_BREAKPOINT_LEN_4;
291 break;
292 #ifdef CONFIG_X86_64
293 case HW_BREAKPOINT_LEN_8:
294 info->len = X86_BREAKPOINT_LEN_8;
295 break;
296 #endif
297 default:
298 return -EINVAL;
299 }
300
301 return 0;
302 }
303 /*
304 * Validate the arch-specific HW Breakpoint register settings
305 */
arch_validate_hwbkpt_settings(struct perf_event * bp)306 int arch_validate_hwbkpt_settings(struct perf_event *bp)
307 {
308 struct arch_hw_breakpoint *info = counter_arch_bp(bp);
309 unsigned int align;
310 int ret;
311
312
313 ret = arch_build_bp_info(bp);
314 if (ret)
315 return ret;
316
317 ret = -EINVAL;
318
319 switch (info->len) {
320 case X86_BREAKPOINT_LEN_1:
321 align = 0;
322 break;
323 case X86_BREAKPOINT_LEN_2:
324 align = 1;
325 break;
326 case X86_BREAKPOINT_LEN_4:
327 align = 3;
328 break;
329 #ifdef CONFIG_X86_64
330 case X86_BREAKPOINT_LEN_8:
331 align = 7;
332 break;
333 #endif
334 default:
335 return ret;
336 }
337
338 /*
339 * Check that the low-order bits of the address are appropriate
340 * for the alignment implied by len.
341 */
342 if (info->address & align)
343 return -EINVAL;
344
345 return 0;
346 }
347
348 /*
349 * Dump the debug register contents to the user.
350 * We can't dump our per cpu values because it
351 * may contain cpu wide breakpoint, something that
352 * doesn't belong to the current task.
353 *
354 * TODO: include non-ptrace user breakpoints (perf)
355 */
aout_dump_debugregs(struct user * dump)356 void aout_dump_debugregs(struct user *dump)
357 {
358 int i;
359 int dr7 = 0;
360 struct perf_event *bp;
361 struct arch_hw_breakpoint *info;
362 struct thread_struct *thread = ¤t->thread;
363
364 for (i = 0; i < HBP_NUM; i++) {
365 bp = thread->ptrace_bps[i];
366
367 if (bp && !bp->attr.disabled) {
368 dump->u_debugreg[i] = bp->attr.bp_addr;
369 info = counter_arch_bp(bp);
370 dr7 |= encode_dr7(i, info->len, info->type);
371 } else {
372 dump->u_debugreg[i] = 0;
373 }
374 }
375
376 dump->u_debugreg[4] = 0;
377 dump->u_debugreg[5] = 0;
378 dump->u_debugreg[6] = current->thread.debugreg6;
379
380 dump->u_debugreg[7] = dr7;
381 }
382 EXPORT_SYMBOL_GPL(aout_dump_debugregs);
383
384 /*
385 * Release the user breakpoints used by ptrace
386 */
flush_ptrace_hw_breakpoint(struct task_struct * tsk)387 void flush_ptrace_hw_breakpoint(struct task_struct *tsk)
388 {
389 int i;
390 struct thread_struct *t = &tsk->thread;
391
392 for (i = 0; i < HBP_NUM; i++) {
393 unregister_hw_breakpoint(t->ptrace_bps[i]);
394 t->ptrace_bps[i] = NULL;
395 }
396 }
397
hw_breakpoint_restore(void)398 void hw_breakpoint_restore(void)
399 {
400 set_debugreg(__this_cpu_read(cpu_debugreg[0]), 0);
401 set_debugreg(__this_cpu_read(cpu_debugreg[1]), 1);
402 set_debugreg(__this_cpu_read(cpu_debugreg[2]), 2);
403 set_debugreg(__this_cpu_read(cpu_debugreg[3]), 3);
404 set_debugreg(current->thread.debugreg6, 6);
405 set_debugreg(__this_cpu_read(cpu_dr7), 7);
406 }
407 EXPORT_SYMBOL_GPL(hw_breakpoint_restore);
408
409 /*
410 * Handle debug exception notifications.
411 *
412 * Return value is either NOTIFY_STOP or NOTIFY_DONE as explained below.
413 *
414 * NOTIFY_DONE returned if one of the following conditions is true.
415 * i) When the causative address is from user-space and the exception
416 * is a valid one, i.e. not triggered as a result of lazy debug register
417 * switching
418 * ii) When there are more bits than trap<n> set in DR6 register (such
419 * as BD, BS or BT) indicating that more than one debug condition is
420 * met and requires some more action in do_debug().
421 *
422 * NOTIFY_STOP returned for all other cases
423 *
424 */
hw_breakpoint_handler(struct die_args * args)425 static int __kprobes hw_breakpoint_handler(struct die_args *args)
426 {
427 int i, cpu, rc = NOTIFY_STOP;
428 struct perf_event *bp;
429 unsigned long dr7, dr6;
430 unsigned long *dr6_p;
431
432 /* The DR6 value is pointed by args->err */
433 dr6_p = (unsigned long *)ERR_PTR(args->err);
434 dr6 = *dr6_p;
435
436 /* If it's a single step, TRAP bits are random */
437 if (dr6 & DR_STEP)
438 return NOTIFY_DONE;
439
440 /* Do an early return if no trap bits are set in DR6 */
441 if ((dr6 & DR_TRAP_BITS) == 0)
442 return NOTIFY_DONE;
443
444 get_debugreg(dr7, 7);
445 /* Disable breakpoints during exception handling */
446 set_debugreg(0UL, 7);
447 /*
448 * Assert that local interrupts are disabled
449 * Reset the DRn bits in the virtualized register value.
450 * The ptrace trigger routine will add in whatever is needed.
451 */
452 current->thread.debugreg6 &= ~DR_TRAP_BITS;
453 cpu = get_cpu();
454
455 /* Handle all the breakpoints that were triggered */
456 for (i = 0; i < HBP_NUM; ++i) {
457 if (likely(!(dr6 & (DR_TRAP0 << i))))
458 continue;
459
460 /*
461 * The counter may be concurrently released but that can only
462 * occur from a call_rcu() path. We can then safely fetch
463 * the breakpoint, use its callback, touch its counter
464 * while we are in an rcu_read_lock() path.
465 */
466 rcu_read_lock();
467
468 bp = per_cpu(bp_per_reg[i], cpu);
469 /*
470 * Reset the 'i'th TRAP bit in dr6 to denote completion of
471 * exception handling
472 */
473 (*dr6_p) &= ~(DR_TRAP0 << i);
474 /*
475 * bp can be NULL due to lazy debug register switching
476 * or due to concurrent perf counter removing.
477 */
478 if (!bp) {
479 rcu_read_unlock();
480 break;
481 }
482
483 perf_bp_event(bp, args->regs);
484
485 /*
486 * Set up resume flag to avoid breakpoint recursion when
487 * returning back to origin.
488 */
489 if (bp->hw.info.type == X86_BREAKPOINT_EXECUTE)
490 args->regs->flags |= X86_EFLAGS_RF;
491
492 rcu_read_unlock();
493 }
494 /*
495 * Further processing in do_debug() is needed for a) user-space
496 * breakpoints (to generate signals) and b) when the system has
497 * taken exception due to multiple causes
498 */
499 if ((current->thread.debugreg6 & DR_TRAP_BITS) ||
500 (dr6 & (~DR_TRAP_BITS)))
501 rc = NOTIFY_DONE;
502
503 set_debugreg(dr7, 7);
504 put_cpu();
505
506 return rc;
507 }
508
509 /*
510 * Handle debug exception notifications.
511 */
hw_breakpoint_exceptions_notify(struct notifier_block * unused,unsigned long val,void * data)512 int __kprobes hw_breakpoint_exceptions_notify(
513 struct notifier_block *unused, unsigned long val, void *data)
514 {
515 if (val != DIE_DEBUG)
516 return NOTIFY_DONE;
517
518 return hw_breakpoint_handler(data);
519 }
520
hw_breakpoint_pmu_read(struct perf_event * bp)521 void hw_breakpoint_pmu_read(struct perf_event *bp)
522 {
523 /* TODO */
524 }
525