1 /*
2 * HW_breakpoint: a unified kernel/user-space hardware breakpoint facility,
3 * using the CPU's debug registers. Derived from
4 * "arch/x86/kernel/hw_breakpoint.c"
5 *
6 * This program is free software; you can redistribute it and/or modify
7 * it under the terms of the GNU General Public License as published by
8 * the Free Software Foundation; either version 2 of the License, or
9 * (at your option) any later version.
10 *
11 * This program is distributed in the hope that it will be useful,
12 * but WITHOUT ANY WARRANTY; without even the implied warranty of
13 * MERCHANTABILITY or FITNESS FOR A PARTICULAR PURPOSE. See the
14 * GNU General Public License for more details.
15 *
16 * You should have received a copy of the GNU General Public License
17 * along with this program; if not, write to the Free Software
18 * Foundation, Inc., 59 Temple Place - Suite 330, Boston, MA 02111-1307, USA.
19 *
20 * Copyright 2010 IBM Corporation
21 * Author: K.Prasad <prasad@linux.vnet.ibm.com>
22 *
23 */
24
25 #include <linux/hw_breakpoint.h>
26 #include <linux/notifier.h>
27 #include <linux/kprobes.h>
28 #include <linux/percpu.h>
29 #include <linux/kernel.h>
30 #include <linux/sched.h>
31 #include <linux/smp.h>
32
33 #include <asm/hw_breakpoint.h>
34 #include <asm/processor.h>
35 #include <asm/sstep.h>
36 #include <asm/uaccess.h>
37
38 /*
39 * Stores the breakpoints currently in use on each breakpoint address
40 * register for every cpu
41 */
42 static DEFINE_PER_CPU(struct perf_event *, bp_per_reg);
43
44 /*
45 * Returns total number of data or instruction breakpoints available.
46 */
hw_breakpoint_slots(int type)47 int hw_breakpoint_slots(int type)
48 {
49 if (type == TYPE_DATA)
50 return HBP_NUM;
51 return 0; /* no instruction breakpoints available */
52 }
53
54 /*
55 * Install a perf counter breakpoint.
56 *
57 * We seek a free debug address register and use it for this
58 * breakpoint.
59 *
60 * Atomic: we hold the counter->ctx->lock and we only handle variables
61 * and registers local to this cpu.
62 */
arch_install_hw_breakpoint(struct perf_event * bp)63 int arch_install_hw_breakpoint(struct perf_event *bp)
64 {
65 struct arch_hw_breakpoint *info = counter_arch_bp(bp);
66 struct perf_event **slot = this_cpu_ptr(&bp_per_reg);
67
68 *slot = bp;
69
70 /*
71 * Do not install DABR values if the instruction must be single-stepped.
72 * If so, DABR will be populated in single_step_dabr_instruction().
73 */
74 if (current->thread.last_hit_ubp != bp)
75 __set_breakpoint(info);
76
77 return 0;
78 }
79
80 /*
81 * Uninstall the breakpoint contained in the given counter.
82 *
83 * First we search the debug address register it uses and then we disable
84 * it.
85 *
86 * Atomic: we hold the counter->ctx->lock and we only handle variables
87 * and registers local to this cpu.
88 */
arch_uninstall_hw_breakpoint(struct perf_event * bp)89 void arch_uninstall_hw_breakpoint(struct perf_event *bp)
90 {
91 struct perf_event **slot = this_cpu_ptr(&bp_per_reg);
92
93 if (*slot != bp) {
94 WARN_ONCE(1, "Can't find the breakpoint");
95 return;
96 }
97
98 *slot = NULL;
99 hw_breakpoint_disable();
100 }
101
102 /*
103 * Perform cleanup of arch-specific counters during unregistration
104 * of the perf-event
105 */
arch_unregister_hw_breakpoint(struct perf_event * bp)106 void arch_unregister_hw_breakpoint(struct perf_event *bp)
107 {
108 /*
109 * If the breakpoint is unregistered between a hw_breakpoint_handler()
110 * and the single_step_dabr_instruction(), then cleanup the breakpoint
111 * restoration variables to prevent dangling pointers.
112 */
113 if (bp->ctx && bp->ctx->task)
114 bp->ctx->task->thread.last_hit_ubp = NULL;
115 }
116
117 /*
118 * Check for virtual address in kernel space.
119 */
arch_check_bp_in_kernelspace(struct perf_event * bp)120 int arch_check_bp_in_kernelspace(struct perf_event *bp)
121 {
122 struct arch_hw_breakpoint *info = counter_arch_bp(bp);
123
124 return is_kernel_addr(info->address);
125 }
126
arch_bp_generic_fields(int type,int * gen_bp_type)127 int arch_bp_generic_fields(int type, int *gen_bp_type)
128 {
129 *gen_bp_type = 0;
130 if (type & HW_BRK_TYPE_READ)
131 *gen_bp_type |= HW_BREAKPOINT_R;
132 if (type & HW_BRK_TYPE_WRITE)
133 *gen_bp_type |= HW_BREAKPOINT_W;
134 if (*gen_bp_type == 0)
135 return -EINVAL;
136 return 0;
137 }
138
139 /*
140 * Validate the arch-specific HW Breakpoint register settings
141 */
arch_validate_hwbkpt_settings(struct perf_event * bp)142 int arch_validate_hwbkpt_settings(struct perf_event *bp)
143 {
144 int ret = -EINVAL, length_max;
145 struct arch_hw_breakpoint *info = counter_arch_bp(bp);
146
147 if (!bp)
148 return ret;
149
150 info->type = HW_BRK_TYPE_TRANSLATE;
151 if (bp->attr.bp_type & HW_BREAKPOINT_R)
152 info->type |= HW_BRK_TYPE_READ;
153 if (bp->attr.bp_type & HW_BREAKPOINT_W)
154 info->type |= HW_BRK_TYPE_WRITE;
155 if (info->type == HW_BRK_TYPE_TRANSLATE)
156 /* must set alteast read or write */
157 return ret;
158 if (!(bp->attr.exclude_user))
159 info->type |= HW_BRK_TYPE_USER;
160 if (!(bp->attr.exclude_kernel))
161 info->type |= HW_BRK_TYPE_KERNEL;
162 if (!(bp->attr.exclude_hv))
163 info->type |= HW_BRK_TYPE_HYP;
164 info->address = bp->attr.bp_addr;
165 info->len = bp->attr.bp_len;
166
167 /*
168 * Since breakpoint length can be a maximum of HW_BREAKPOINT_LEN(8)
169 * and breakpoint addresses are aligned to nearest double-word
170 * HW_BREAKPOINT_ALIGN by rounding off to the lower address, the
171 * 'symbolsize' should satisfy the check below.
172 */
173 length_max = 8; /* DABR */
174 if (cpu_has_feature(CPU_FTR_DAWR)) {
175 length_max = 512 ; /* 64 doublewords */
176 /* DAWR region can't cross 512 boundary */
177 if ((bp->attr.bp_addr >> 9) !=
178 ((bp->attr.bp_addr + bp->attr.bp_len - 1) >> 9))
179 return -EINVAL;
180 }
181 if (info->len >
182 (length_max - (info->address & HW_BREAKPOINT_ALIGN)))
183 return -EINVAL;
184 return 0;
185 }
186
187 /*
188 * Restores the breakpoint on the debug registers.
189 * Invoke this function if it is known that the execution context is
190 * about to change to cause loss of MSR_SE settings.
191 */
thread_change_pc(struct task_struct * tsk,struct pt_regs * regs)192 void thread_change_pc(struct task_struct *tsk, struct pt_regs *regs)
193 {
194 struct arch_hw_breakpoint *info;
195
196 if (likely(!tsk->thread.last_hit_ubp))
197 return;
198
199 info = counter_arch_bp(tsk->thread.last_hit_ubp);
200 regs->msr &= ~MSR_SE;
201 __set_breakpoint(info);
202 tsk->thread.last_hit_ubp = NULL;
203 }
204
205 /*
206 * Handle debug exception notifications.
207 */
hw_breakpoint_handler(struct die_args * args)208 int __kprobes hw_breakpoint_handler(struct die_args *args)
209 {
210 int rc = NOTIFY_STOP;
211 struct perf_event *bp;
212 struct pt_regs *regs = args->regs;
213 int stepped = 1;
214 struct arch_hw_breakpoint *info;
215 unsigned int instr;
216 unsigned long dar = regs->dar;
217
218 /* Disable breakpoints during exception handling */
219 hw_breakpoint_disable();
220
221 /*
222 * The counter may be concurrently released but that can only
223 * occur from a call_rcu() path. We can then safely fetch
224 * the breakpoint, use its callback, touch its counter
225 * while we are in an rcu_read_lock() path.
226 */
227 rcu_read_lock();
228
229 bp = __this_cpu_read(bp_per_reg);
230 if (!bp) {
231 rc = NOTIFY_DONE;
232 goto out;
233 }
234 info = counter_arch_bp(bp);
235
236 /*
237 * Return early after invoking user-callback function without restoring
238 * DABR if the breakpoint is from ptrace which always operates in
239 * one-shot mode. The ptrace-ed process will receive the SIGTRAP signal
240 * generated in do_dabr().
241 */
242 if (bp->overflow_handler == ptrace_triggered) {
243 perf_bp_event(bp, regs);
244 rc = NOTIFY_DONE;
245 goto out;
246 }
247
248 /*
249 * Verify if dar lies within the address range occupied by the symbol
250 * being watched to filter extraneous exceptions. If it doesn't,
251 * we still need to single-step the instruction, but we don't
252 * generate an event.
253 */
254 info->type &= ~HW_BRK_TYPE_EXTRANEOUS_IRQ;
255 if (!((bp->attr.bp_addr <= dar) &&
256 (dar - bp->attr.bp_addr < bp->attr.bp_len)))
257 info->type |= HW_BRK_TYPE_EXTRANEOUS_IRQ;
258
259 /* Do not emulate user-space instructions, instead single-step them */
260 if (user_mode(regs)) {
261 current->thread.last_hit_ubp = bp;
262 regs->msr |= MSR_SE;
263 goto out;
264 }
265
266 stepped = 0;
267 instr = 0;
268 if (!__get_user_inatomic(instr, (unsigned int *) regs->nip))
269 stepped = emulate_step(regs, instr);
270
271 /*
272 * emulate_step() could not execute it. We've failed in reliably
273 * handling the hw-breakpoint. Unregister it and throw a warning
274 * message to let the user know about it.
275 */
276 if (!stepped) {
277 WARN(1, "Unable to handle hardware breakpoint. Breakpoint at "
278 "0x%lx will be disabled.", info->address);
279 perf_event_disable(bp);
280 goto out;
281 }
282 /*
283 * As a policy, the callback is invoked in a 'trigger-after-execute'
284 * fashion
285 */
286 if (!(info->type & HW_BRK_TYPE_EXTRANEOUS_IRQ))
287 perf_bp_event(bp, regs);
288
289 __set_breakpoint(info);
290 out:
291 rcu_read_unlock();
292 return rc;
293 }
294
295 /*
296 * Handle single-step exceptions following a DABR hit.
297 */
single_step_dabr_instruction(struct die_args * args)298 static int __kprobes single_step_dabr_instruction(struct die_args *args)
299 {
300 struct pt_regs *regs = args->regs;
301 struct perf_event *bp = NULL;
302 struct arch_hw_breakpoint *info;
303
304 bp = current->thread.last_hit_ubp;
305 /*
306 * Check if we are single-stepping as a result of a
307 * previous HW Breakpoint exception
308 */
309 if (!bp)
310 return NOTIFY_DONE;
311
312 info = counter_arch_bp(bp);
313
314 /*
315 * We shall invoke the user-defined callback function in the single
316 * stepping handler to confirm to 'trigger-after-execute' semantics
317 */
318 if (!(info->type & HW_BRK_TYPE_EXTRANEOUS_IRQ))
319 perf_bp_event(bp, regs);
320
321 __set_breakpoint(info);
322 current->thread.last_hit_ubp = NULL;
323
324 /*
325 * If the process was being single-stepped by ptrace, let the
326 * other single-step actions occur (e.g. generate SIGTRAP).
327 */
328 if (test_thread_flag(TIF_SINGLESTEP))
329 return NOTIFY_DONE;
330
331 return NOTIFY_STOP;
332 }
333
334 /*
335 * Handle debug exception notifications.
336 */
hw_breakpoint_exceptions_notify(struct notifier_block * unused,unsigned long val,void * data)337 int __kprobes hw_breakpoint_exceptions_notify(
338 struct notifier_block *unused, unsigned long val, void *data)
339 {
340 int ret = NOTIFY_DONE;
341
342 switch (val) {
343 case DIE_DABR_MATCH:
344 ret = hw_breakpoint_handler(data);
345 break;
346 case DIE_SSTEP:
347 ret = single_step_dabr_instruction(data);
348 break;
349 }
350
351 return ret;
352 }
353
354 /*
355 * Release the user breakpoints used by ptrace
356 */
flush_ptrace_hw_breakpoint(struct task_struct * tsk)357 void flush_ptrace_hw_breakpoint(struct task_struct *tsk)
358 {
359 struct thread_struct *t = &tsk->thread;
360
361 unregister_hw_breakpoint(t->ptrace_bps[0]);
362 t->ptrace_bps[0] = NULL;
363 }
364
hw_breakpoint_pmu_read(struct perf_event * bp)365 void hw_breakpoint_pmu_read(struct perf_event *bp)
366 {
367 /* TODO */
368 }
369