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"
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.
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.
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.
20 * Copyright 2010 IBM Corporation
21 * Author: K.Prasad <prasad@linux.vnet.ibm.com>
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/module.h>
31 #include <linux/sched.h>
32 #include <linux/init.h>
33 #include <linux/smp.h>
35 #include <asm/hw_breakpoint.h>
36 #include <asm/processor.h>
37 #include <asm/sstep.h>
38 #include <asm/uaccess.h>
41 * Stores the breakpoints currently in use on each breakpoint address
42 * register for every cpu
44 static DEFINE_PER_CPU(struct perf_event *, bp_per_reg);
47 * Install a perf counter breakpoint.
49 * We seek a free debug address register and use it for this
52 * Atomic: we hold the counter->ctx->lock and we only handle variables
53 * and registers local to this cpu.
55 int arch_install_hw_breakpoint(struct perf_event *bp)
57 struct arch_hw_breakpoint *info = counter_arch_bp(bp);
58 struct perf_event **slot = &__get_cpu_var(bp_per_reg);
63 * Do not install DABR values if the instruction must be single-stepped.
64 * If so, DABR will be populated in single_step_dabr_instruction().
66 if (current->thread.last_hit_ubp != bp)
67 set_dabr(info->address | info->type | DABR_TRANSLATION);
73 * Uninstall the breakpoint contained in the given counter.
75 * First we search the debug address register it uses and then we disable
78 * Atomic: we hold the counter->ctx->lock and we only handle variables
79 * and registers local to this cpu.
81 void arch_uninstall_hw_breakpoint(struct perf_event *bp)
83 struct perf_event **slot = &__get_cpu_var(bp_per_reg);
86 WARN_ONCE(1, "Can't find the breakpoint");
95 * Perform cleanup of arch-specific counters during unregistration
98 void arch_unregister_hw_breakpoint(struct perf_event *bp)
101 * If the breakpoint is unregistered between a hw_breakpoint_handler()
102 * and the single_step_dabr_instruction(), then cleanup the breakpoint
103 * restoration variables to prevent dangling pointers.
106 bp->ctx->task->thread.last_hit_ubp = NULL;
110 * Check for virtual address in kernel space.
112 int arch_check_bp_in_kernelspace(struct perf_event *bp)
114 struct arch_hw_breakpoint *info = counter_arch_bp(bp);
116 return is_kernel_addr(info->address);
119 int arch_bp_generic_fields(int type, int *gen_bp_type)
123 *gen_bp_type = HW_BREAKPOINT_R;
125 case DABR_DATA_WRITE:
126 *gen_bp_type = HW_BREAKPOINT_W;
128 case (DABR_DATA_WRITE | DABR_DATA_READ):
129 *gen_bp_type = (HW_BREAKPOINT_W | HW_BREAKPOINT_R);
138 * Validate the arch-specific HW Breakpoint register settings
140 int arch_validate_hwbkpt_settings(struct perf_event *bp)
143 struct arch_hw_breakpoint *info = counter_arch_bp(bp);
148 switch (bp->attr.bp_type) {
149 case HW_BREAKPOINT_R:
150 info->type = DABR_DATA_READ;
152 case HW_BREAKPOINT_W:
153 info->type = DABR_DATA_WRITE;
155 case HW_BREAKPOINT_R | HW_BREAKPOINT_W:
156 info->type = (DABR_DATA_READ | DABR_DATA_WRITE);
162 info->address = bp->attr.bp_addr;
163 info->len = bp->attr.bp_len;
166 * Since breakpoint length can be a maximum of HW_BREAKPOINT_LEN(8)
167 * and breakpoint addresses are aligned to nearest double-word
168 * HW_BREAKPOINT_ALIGN by rounding off to the lower address, the
169 * 'symbolsize' should satisfy the check below.
172 (HW_BREAKPOINT_LEN - (info->address & HW_BREAKPOINT_ALIGN)))
178 * Restores the breakpoint on the debug registers.
179 * Invoke this function if it is known that the execution context is
180 * about to change to cause loss of MSR_SE settings.
182 void thread_change_pc(struct task_struct *tsk, struct pt_regs *regs)
184 struct arch_hw_breakpoint *info;
186 if (likely(!tsk->thread.last_hit_ubp))
189 info = counter_arch_bp(tsk->thread.last_hit_ubp);
190 regs->msr &= ~MSR_SE;
191 set_dabr(info->address | info->type | DABR_TRANSLATION);
192 tsk->thread.last_hit_ubp = NULL;
196 * Handle debug exception notifications.
198 int __kprobes hw_breakpoint_handler(struct die_args *args)
200 bool is_ptrace_bp = false;
201 int rc = NOTIFY_STOP;
202 struct perf_event *bp;
203 struct pt_regs *regs = args->regs;
205 struct arch_hw_breakpoint *info;
207 unsigned long dar = regs->dar;
209 /* Disable breakpoints during exception handling */
212 * The counter may be concurrently released but that can only
213 * occur from a call_rcu() path. We can then safely fetch
214 * the breakpoint, use its callback, touch its counter
215 * while we are in an rcu_read_lock() path.
219 bp = __get_cpu_var(bp_per_reg);
222 info = counter_arch_bp(bp);
223 is_ptrace_bp = (bp->overflow_handler == ptrace_triggered) ?
227 * Return early after invoking user-callback function without restoring
228 * DABR if the breakpoint is from ptrace which always operates in
229 * one-shot mode. The ptrace-ed process will receive the SIGTRAP signal
230 * generated in do_dabr().
233 perf_bp_event(bp, regs);
239 * Verify if dar lies within the address range occupied by the symbol
240 * being watched to filter extraneous exceptions.
242 if (!((bp->attr.bp_addr <= dar) &&
243 (dar <= (bp->attr.bp_addr + bp->attr.bp_len)))) {
245 * This exception is triggered not because of a memory access
246 * on the monitored variable but in the double-word address
247 * range in which it is contained. We will consume this
248 * exception, considering it as 'noise'.
250 info->extraneous_interrupt = true;
252 info->extraneous_interrupt = false;
254 /* Do not emulate user-space instructions, instead single-step them */
255 if (user_mode(regs)) {
256 bp->ctx->task->thread.last_hit_ubp = bp;
263 if (!__get_user_inatomic(instr, (unsigned int *) regs->nip))
264 stepped = emulate_step(regs, instr);
267 * emulate_step() could not execute it. We've failed in reliably
268 * handling the hw-breakpoint. Unregister it and throw a warning
269 * message to let the user know about it.
272 WARN(1, "Unable to handle hardware breakpoint. Breakpoint at "
273 "0x%lx will be disabled.", info->address);
274 perf_event_disable(bp);
278 * As a policy, the callback is invoked in a 'trigger-after-execute'
281 if (!info->extraneous_interrupt)
282 perf_bp_event(bp, regs);
284 set_dabr(info->address | info->type | DABR_TRANSLATION);
291 * Handle single-step exceptions following a DABR hit.
293 int __kprobes single_step_dabr_instruction(struct die_args *args)
295 struct pt_regs *regs = args->regs;
296 struct perf_event *bp = NULL;
297 struct arch_hw_breakpoint *bp_info;
299 bp = current->thread.last_hit_ubp;
301 * Check if we are single-stepping as a result of a
302 * previous HW Breakpoint exception
307 bp_info = counter_arch_bp(bp);
310 * We shall invoke the user-defined callback function in the single
311 * stepping handler to confirm to 'trigger-after-execute' semantics
313 if (!bp_info->extraneous_interrupt)
314 perf_bp_event(bp, regs);
317 * Do not disable MSR_SE if the process was already in
318 * single-stepping mode.
320 if (!test_thread_flag(TIF_SINGLESTEP))
321 regs->msr &= ~MSR_SE;
323 set_dabr(bp_info->address | bp_info->type | DABR_TRANSLATION);
324 current->thread.last_hit_ubp = NULL;
329 * Handle debug exception notifications.
331 int __kprobes hw_breakpoint_exceptions_notify(
332 struct notifier_block *unused, unsigned long val, void *data)
334 int ret = NOTIFY_DONE;
338 ret = hw_breakpoint_handler(data);
341 ret = single_step_dabr_instruction(data);
349 * Release the user breakpoints used by ptrace
351 void flush_ptrace_hw_breakpoint(struct task_struct *tsk)
353 struct thread_struct *t = &tsk->thread;
355 unregister_hw_breakpoint(t->ptrace_bps[0]);
356 t->ptrace_bps[0] = NULL;
359 void hw_breakpoint_pmu_read(struct perf_event *bp)