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Linux/arch/powerpc/kernel/hw_breakpoint.c

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  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          * FIXME, this should not be using bp->ctx at all! Sayeth peterz.
113          */
114         if (bp->ctx && bp->ctx->task && bp->ctx->task != ((void *)-1L))
115                 bp->ctx->task->thread.last_hit_ubp = NULL;
116 }
117 
118 /*
119  * Check for virtual address in kernel space.
120  */
121 int arch_check_bp_in_kernelspace(struct perf_event *bp)
122 {
123         struct arch_hw_breakpoint *info = counter_arch_bp(bp);
124 
125         return is_kernel_addr(info->address);
126 }
127 
128 int arch_bp_generic_fields(int type, int *gen_bp_type)
129 {
130         *gen_bp_type = 0;
131         if (type & HW_BRK_TYPE_READ)
132                 *gen_bp_type |= HW_BREAKPOINT_R;
133         if (type & HW_BRK_TYPE_WRITE)
134                 *gen_bp_type |= HW_BREAKPOINT_W;
135         if (*gen_bp_type == 0)
136                 return -EINVAL;
137         return 0;
138 }
139 
140 /*
141  * Validate the arch-specific HW Breakpoint register settings
142  */
143 int arch_validate_hwbkpt_settings(struct perf_event *bp)
144 {
145         int ret = -EINVAL, length_max;
146         struct arch_hw_breakpoint *info = counter_arch_bp(bp);
147 
148         if (!bp)
149                 return ret;
150 
151         info->type = HW_BRK_TYPE_TRANSLATE;
152         if (bp->attr.bp_type & HW_BREAKPOINT_R)
153                 info->type |= HW_BRK_TYPE_READ;
154         if (bp->attr.bp_type & HW_BREAKPOINT_W)
155                 info->type |= HW_BRK_TYPE_WRITE;
156         if (info->type == HW_BRK_TYPE_TRANSLATE)
157                 /* must set alteast read or write */
158                 return ret;
159         if (!(bp->attr.exclude_user))
160                 info->type |= HW_BRK_TYPE_USER;
161         if (!(bp->attr.exclude_kernel))
162                 info->type |= HW_BRK_TYPE_KERNEL;
163         if (!(bp->attr.exclude_hv))
164                 info->type |= HW_BRK_TYPE_HYP;
165         info->address = bp->attr.bp_addr;
166         info->len = bp->attr.bp_len;
167 
168         /*
169          * Since breakpoint length can be a maximum of HW_BREAKPOINT_LEN(8)
170          * and breakpoint addresses are aligned to nearest double-word
171          * HW_BREAKPOINT_ALIGN by rounding off to the lower address, the
172          * 'symbolsize' should satisfy the check below.
173          */
174         length_max = 8; /* DABR */
175         if (cpu_has_feature(CPU_FTR_DAWR)) {
176                 length_max = 512 ; /* 64 doublewords */
177                 /* DAWR region can't cross 512 boundary */
178                 if ((bp->attr.bp_addr >> 10) != 
179                     ((bp->attr.bp_addr + bp->attr.bp_len - 1) >> 10))
180                         return -EINVAL;
181         }
182         if (info->len >
183             (length_max - (info->address & HW_BREAKPOINT_ALIGN)))
184                 return -EINVAL;
185         return 0;
186 }
187 
188 /*
189  * Restores the breakpoint on the debug registers.
190  * Invoke this function if it is known that the execution context is
191  * about to change to cause loss of MSR_SE settings.
192  */
193 void thread_change_pc(struct task_struct *tsk, struct pt_regs *regs)
194 {
195         struct arch_hw_breakpoint *info;
196 
197         if (likely(!tsk->thread.last_hit_ubp))
198                 return;
199 
200         info = counter_arch_bp(tsk->thread.last_hit_ubp);
201         regs->msr &= ~MSR_SE;
202         __set_breakpoint(info);
203         tsk->thread.last_hit_ubp = NULL;
204 }
205 
206 /*
207  * Handle debug exception notifications.
208  */
209 int __kprobes hw_breakpoint_handler(struct die_args *args)
210 {
211         int rc = NOTIFY_STOP;
212         struct perf_event *bp;
213         struct pt_regs *regs = args->regs;
214         int stepped = 1;
215         struct arch_hw_breakpoint *info;
216         unsigned int instr;
217         unsigned long dar = regs->dar;
218 
219         /* Disable breakpoints during exception handling */
220         hw_breakpoint_disable();
221 
222         /*
223          * The counter may be concurrently released but that can only
224          * occur from a call_rcu() path. We can then safely fetch
225          * the breakpoint, use its callback, touch its counter
226          * while we are in an rcu_read_lock() path.
227          */
228         rcu_read_lock();
229 
230         bp = __this_cpu_read(bp_per_reg);
231         if (!bp)
232                 goto out;
233         info = counter_arch_bp(bp);
234 
235         /*
236          * Return early after invoking user-callback function without restoring
237          * DABR if the breakpoint is from ptrace which always operates in
238          * one-shot mode. The ptrace-ed process will receive the SIGTRAP signal
239          * generated in do_dabr().
240          */
241         if (bp->overflow_handler == ptrace_triggered) {
242                 perf_bp_event(bp, regs);
243                 rc = NOTIFY_DONE;
244                 goto out;
245         }
246 
247         /*
248          * Verify if dar lies within the address range occupied by the symbol
249          * being watched to filter extraneous exceptions.  If it doesn't,
250          * we still need to single-step the instruction, but we don't
251          * generate an event.
252          */
253         info->type &= ~HW_BRK_TYPE_EXTRANEOUS_IRQ;
254         if (!((bp->attr.bp_addr <= dar) &&
255               (dar - bp->attr.bp_addr < bp->attr.bp_len)))
256                 info->type |= HW_BRK_TYPE_EXTRANEOUS_IRQ;
257 
258         /* Do not emulate user-space instructions, instead single-step them */
259         if (user_mode(regs)) {
260                 current->thread.last_hit_ubp = bp;
261                 regs->msr |= MSR_SE;
262                 goto out;
263         }
264 
265         stepped = 0;
266         instr = 0;
267         if (!__get_user_inatomic(instr, (unsigned int *) regs->nip))
268                 stepped = emulate_step(regs, instr);
269 
270         /*
271          * emulate_step() could not execute it. We've failed in reliably
272          * handling the hw-breakpoint. Unregister it and throw a warning
273          * message to let the user know about it.
274          */
275         if (!stepped) {
276                 WARN(1, "Unable to handle hardware breakpoint. Breakpoint at "
277                         "0x%lx will be disabled.", info->address);
278                 perf_event_disable(bp);
279                 goto out;
280         }
281         /*
282          * As a policy, the callback is invoked in a 'trigger-after-execute'
283          * fashion
284          */
285         if (!(info->type & HW_BRK_TYPE_EXTRANEOUS_IRQ))
286                 perf_bp_event(bp, regs);
287 
288         __set_breakpoint(info);
289 out:
290         rcu_read_unlock();
291         return rc;
292 }
293 
294 /*
295  * Handle single-step exceptions following a DABR hit.
296  */
297 static int __kprobes single_step_dabr_instruction(struct die_args *args)
298 {
299         struct pt_regs *regs = args->regs;
300         struct perf_event *bp = NULL;
301         struct arch_hw_breakpoint *info;
302 
303         bp = current->thread.last_hit_ubp;
304         /*
305          * Check if we are single-stepping as a result of a
306          * previous HW Breakpoint exception
307          */
308         if (!bp)
309                 return NOTIFY_DONE;
310 
311         info = counter_arch_bp(bp);
312 
313         /*
314          * We shall invoke the user-defined callback function in the single
315          * stepping handler to confirm to 'trigger-after-execute' semantics
316          */
317         if (!(info->type & HW_BRK_TYPE_EXTRANEOUS_IRQ))
318                 perf_bp_event(bp, regs);
319 
320         __set_breakpoint(info);
321         current->thread.last_hit_ubp = NULL;
322 
323         /*
324          * If the process was being single-stepped by ptrace, let the
325          * other single-step actions occur (e.g. generate SIGTRAP).
326          */
327         if (test_thread_flag(TIF_SINGLESTEP))
328                 return NOTIFY_DONE;
329 
330         return NOTIFY_STOP;
331 }
332 
333 /*
334  * Handle debug exception notifications.
335  */
336 int __kprobes hw_breakpoint_exceptions_notify(
337                 struct notifier_block *unused, unsigned long val, void *data)
338 {
339         int ret = NOTIFY_DONE;
340 
341         switch (val) {
342         case DIE_DABR_MATCH:
343                 ret = hw_breakpoint_handler(data);
344                 break;
345         case DIE_SSTEP:
346                 ret = single_step_dabr_instruction(data);
347                 break;
348         }
349 
350         return ret;
351 }
352 
353 /*
354  * Release the user breakpoints used by ptrace
355  */
356 void flush_ptrace_hw_breakpoint(struct task_struct *tsk)
357 {
358         struct thread_struct *t = &tsk->thread;
359 
360         unregister_hw_breakpoint(t->ptrace_bps[0]);
361         t->ptrace_bps[0] = NULL;
362 }
363 
364 void hw_breakpoint_pmu_read(struct perf_event *bp)
365 {
366         /* TODO */
367 }
368 

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