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 */
42static DEFINE_PER_CPU(struct perf_event *, bp_per_reg);
43
44/*
45 * Returns total number of data or instruction breakpoints available.
46 */
47int 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 */
63int 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 */
89void 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 */
106void 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 */
120int 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
127int 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 */
142int 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 >> 10) !=
178		    ((bp->attr.bp_addr + bp->attr.bp_len - 1) >> 10))
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 */
192void 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 */
208int __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		goto out;
232	info = counter_arch_bp(bp);
233
234	/*
235	 * Return early after invoking user-callback function without restoring
236	 * DABR if the breakpoint is from ptrace which always operates in
237	 * one-shot mode. The ptrace-ed process will receive the SIGTRAP signal
238	 * generated in do_dabr().
239	 */
240	if (bp->overflow_handler == ptrace_triggered) {
241		perf_bp_event(bp, regs);
242		rc = NOTIFY_DONE;
243		goto out;
244	}
245
246	/*
247	 * Verify if dar lies within the address range occupied by the symbol
248	 * being watched to filter extraneous exceptions.  If it doesn't,
249	 * we still need to single-step the instruction, but we don't
250	 * generate an event.
251	 */
252	info->type &= ~HW_BRK_TYPE_EXTRANEOUS_IRQ;
253	if (!((bp->attr.bp_addr <= dar) &&
254	      (dar - bp->attr.bp_addr < bp->attr.bp_len)))
255		info->type |= HW_BRK_TYPE_EXTRANEOUS_IRQ;
256
257	/* Do not emulate user-space instructions, instead single-step them */
258	if (user_mode(regs)) {
259		current->thread.last_hit_ubp = bp;
260		regs->msr |= MSR_SE;
261		goto out;
262	}
263
264	stepped = 0;
265	instr = 0;
266	if (!__get_user_inatomic(instr, (unsigned int *) regs->nip))
267		stepped = emulate_step(regs, instr);
268
269	/*
270	 * emulate_step() could not execute it. We've failed in reliably
271	 * handling the hw-breakpoint. Unregister it and throw a warning
272	 * message to let the user know about it.
273	 */
274	if (!stepped) {
275		WARN(1, "Unable to handle hardware breakpoint. Breakpoint at "
276			"0x%lx will be disabled.", info->address);
277		perf_event_disable(bp);
278		goto out;
279	}
280	/*
281	 * As a policy, the callback is invoked in a 'trigger-after-execute'
282	 * fashion
283	 */
284	if (!(info->type & HW_BRK_TYPE_EXTRANEOUS_IRQ))
285		perf_bp_event(bp, regs);
286
287	__set_breakpoint(info);
288out:
289	rcu_read_unlock();
290	return rc;
291}
292
293/*
294 * Handle single-step exceptions following a DABR hit.
295 */
296static int __kprobes single_step_dabr_instruction(struct die_args *args)
297{
298	struct pt_regs *regs = args->regs;
299	struct perf_event *bp = NULL;
300	struct arch_hw_breakpoint *info;
301
302	bp = current->thread.last_hit_ubp;
303	/*
304	 * Check if we are single-stepping as a result of a
305	 * previous HW Breakpoint exception
306	 */
307	if (!bp)
308		return NOTIFY_DONE;
309
310	info = counter_arch_bp(bp);
311
312	/*
313	 * We shall invoke the user-defined callback function in the single
314	 * stepping handler to confirm to 'trigger-after-execute' semantics
315	 */
316	if (!(info->type & HW_BRK_TYPE_EXTRANEOUS_IRQ))
317		perf_bp_event(bp, regs);
318
319	__set_breakpoint(info);
320	current->thread.last_hit_ubp = NULL;
321
322	/*
323	 * If the process was being single-stepped by ptrace, let the
324	 * other single-step actions occur (e.g. generate SIGTRAP).
325	 */
326	if (test_thread_flag(TIF_SINGLESTEP))
327		return NOTIFY_DONE;
328
329	return NOTIFY_STOP;
330}
331
332/*
333 * Handle debug exception notifications.
334 */
335int __kprobes hw_breakpoint_exceptions_notify(
336		struct notifier_block *unused, unsigned long val, void *data)
337{
338	int ret = NOTIFY_DONE;
339
340	switch (val) {
341	case DIE_DABR_MATCH:
342		ret = hw_breakpoint_handler(data);
343		break;
344	case DIE_SSTEP:
345		ret = single_step_dabr_instruction(data);
346		break;
347	}
348
349	return ret;
350}
351
352/*
353 * Release the user breakpoints used by ptrace
354 */
355void flush_ptrace_hw_breakpoint(struct task_struct *tsk)
356{
357	struct thread_struct *t = &tsk->thread;
358
359	unregister_hw_breakpoint(t->ptrace_bps[0]);
360	t->ptrace_bps[0] = NULL;
361}
362
363void hw_breakpoint_pmu_read(struct perf_event *bp)
364{
365	/* TODO */
366}
367