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  */
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  */
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  */
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  */
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  */
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 
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  */
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 >> 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  */
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  */
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 		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);
288 out:
289 	rcu_read_unlock();
290 	return rc;
291 }
292 
293 /*
294  * Handle single-step exceptions following a DABR hit.
295  */
296 static 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  */
335 int __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  */
355 void 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 
363 void hw_breakpoint_pmu_read(struct perf_event *bp)
364 {
365 	/* TODO */
366 }
367