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1 | /* |
2 | * This program is free software; you can redistribute it and/or modify | |
3 | * it under the terms of the GNU General Public License as published by | |
4 | * the Free Software Foundation; either version 2 of the License, or | |
5 | * (at your option) any later version. | |
6 | * | |
7 | * This program is distributed in the hope that it will be useful, | |
8 | * but WITHOUT ANY WARRANTY; without even the implied warranty of | |
9 | * MERCHANTABILITY or FITNESS FOR A PARTICULAR PURPOSE. See the | |
10 | * GNU General Public License for more details. | |
11 | * | |
12 | * You should have received a copy of the GNU General Public License | |
13 | * along with this program; if not, write to the Free Software | |
14 | * Foundation, Inc., 59 Temple Place - Suite 330, Boston, MA 02111-1307, USA. | |
15 | * | |
16 | * Copyright (C) 2007 Alan Stern | |
17 | * Copyright (C) IBM Corporation, 2009 | |
18 | */ | |
19 | ||
20 | /* | |
21 | * HW_breakpoint: a unified kernel/user-space hardware breakpoint facility, | |
22 | * using the CPU's debug registers. | |
23 | * This file contains the arch-independent routines. | |
24 | */ | |
25 | ||
26 | #include <linux/irqflags.h> | |
27 | #include <linux/kallsyms.h> | |
28 | #include <linux/notifier.h> | |
29 | #include <linux/kprobes.h> | |
30 | #include <linux/kdebug.h> | |
31 | #include <linux/kernel.h> | |
32 | #include <linux/module.h> | |
33 | #include <linux/percpu.h> | |
34 | #include <linux/sched.h> | |
35 | #include <linux/init.h> | |
36 | #include <linux/smp.h> | |
37 | ||
38 | #include <asm/hw_breakpoint.h> | |
39 | #include <asm/processor.h> | |
40 | ||
41 | #ifdef CONFIG_X86 | |
42 | #include <asm/debugreg.h> | |
43 | #endif | |
44 | /* | |
45 | * Spinlock that protects all (un)register operations over kernel/user-space | |
46 | * breakpoint requests | |
47 | */ | |
48 | static DEFINE_SPINLOCK(hw_breakpoint_lock); | |
49 | ||
50 | /* Array of kernel-space breakpoint structures */ | |
51 | struct hw_breakpoint *hbp_kernel[HBP_NUM]; | |
52 | ||
53 | /* | |
54 | * Per-processor copy of hbp_kernel[]. Used only when hbp_kernel is being | |
55 | * modified but we need the older copy to handle any hbp exceptions. It will | |
56 | * sync with hbp_kernel[] value after updation is done through IPIs. | |
57 | */ | |
58 | DEFINE_PER_CPU(struct hw_breakpoint*, this_hbp_kernel[HBP_NUM]); | |
59 | ||
60 | /* | |
61 | * Kernel breakpoints grow downwards, starting from HBP_NUM | |
62 | * 'hbp_kernel_pos' denotes lowest numbered breakpoint register occupied for | |
63 | * kernel-space request. We will initialise it here and not in an __init | |
64 | * routine because load_debug_registers(), which uses this variable can be | |
65 | * called very early during CPU initialisation. | |
66 | */ | |
67 | unsigned int hbp_kernel_pos = HBP_NUM; | |
68 | ||
69 | /* | |
70 | * An array containing refcount of threads using a given bkpt register | |
71 | * Accesses are synchronised by acquiring hw_breakpoint_lock | |
72 | */ | |
73 | unsigned int hbp_user_refcount[HBP_NUM]; | |
74 | ||
75 | /* | |
76 | * Load the debug registers during startup of a CPU. | |
77 | */ | |
78 | void load_debug_registers(void) | |
79 | { | |
80 | unsigned long flags; | |
81 | struct task_struct *tsk = current; | |
82 | ||
83 | spin_lock_bh(&hw_breakpoint_lock); | |
84 | ||
85 | /* Prevent IPIs for new kernel breakpoint updates */ | |
86 | local_irq_save(flags); | |
87 | arch_update_kernel_hw_breakpoint(NULL); | |
88 | local_irq_restore(flags); | |
89 | ||
90 | if (test_tsk_thread_flag(tsk, TIF_DEBUG)) | |
91 | arch_install_thread_hw_breakpoint(tsk); | |
92 | ||
93 | spin_unlock_bh(&hw_breakpoint_lock); | |
94 | } | |
95 | ||
96 | /* | |
97 | * Erase all the hardware breakpoint info associated with a thread. | |
98 | * | |
99 | * If tsk != current then tsk must not be usable (for example, a | |
100 | * child being cleaned up from a failed fork). | |
101 | */ | |
102 | void flush_thread_hw_breakpoint(struct task_struct *tsk) | |
103 | { | |
104 | int i; | |
105 | struct thread_struct *thread = &(tsk->thread); | |
106 | ||
107 | spin_lock_bh(&hw_breakpoint_lock); | |
108 | ||
109 | /* The thread no longer has any breakpoints associated with it */ | |
110 | clear_tsk_thread_flag(tsk, TIF_DEBUG); | |
111 | for (i = 0; i < HBP_NUM; i++) { | |
112 | if (thread->hbp[i]) { | |
113 | hbp_user_refcount[i]--; | |
114 | kfree(thread->hbp[i]); | |
115 | thread->hbp[i] = NULL; | |
116 | } | |
117 | } | |
118 | ||
119 | arch_flush_thread_hw_breakpoint(tsk); | |
120 | ||
121 | /* Actually uninstall the breakpoints if necessary */ | |
122 | if (tsk == current) | |
123 | arch_uninstall_thread_hw_breakpoint(); | |
124 | spin_unlock_bh(&hw_breakpoint_lock); | |
125 | } | |
126 | ||
127 | /* | |
128 | * Copy the hardware breakpoint info from a thread to its cloned child. | |
129 | */ | |
130 | int copy_thread_hw_breakpoint(struct task_struct *tsk, | |
131 | struct task_struct *child, unsigned long clone_flags) | |
132 | { | |
133 | /* | |
134 | * We will assume that breakpoint settings are not inherited | |
135 | * and the child starts out with no debug registers set. | |
136 | * But what about CLONE_PTRACE? | |
137 | */ | |
138 | clear_tsk_thread_flag(child, TIF_DEBUG); | |
139 | ||
140 | /* We will call flush routine since the debugregs are not inherited */ | |
141 | arch_flush_thread_hw_breakpoint(child); | |
142 | ||
143 | return 0; | |
144 | } | |
145 | ||
146 | static int __register_user_hw_breakpoint(int pos, struct task_struct *tsk, | |
147 | struct hw_breakpoint *bp) | |
148 | { | |
149 | struct thread_struct *thread = &(tsk->thread); | |
150 | int rc; | |
151 | ||
152 | /* Do not overcommit. Fail if kernel has used the hbp registers */ | |
153 | if (pos >= hbp_kernel_pos) | |
154 | return -ENOSPC; | |
155 | ||
156 | rc = arch_validate_hwbkpt_settings(bp, tsk); | |
157 | if (rc) | |
158 | return rc; | |
159 | ||
160 | thread->hbp[pos] = bp; | |
161 | hbp_user_refcount[pos]++; | |
162 | ||
163 | arch_update_user_hw_breakpoint(pos, tsk); | |
164 | /* | |
165 | * Does it need to be installed right now? | |
166 | * Otherwise it will get installed the next time tsk runs | |
167 | */ | |
168 | if (tsk == current) | |
169 | arch_install_thread_hw_breakpoint(tsk); | |
170 | ||
171 | return rc; | |
172 | } | |
173 | ||
174 | /* | |
175 | * Modify the address of a hbp register already in use by the task | |
176 | * Do not invoke this in-lieu of a __unregister_user_hw_breakpoint() | |
177 | */ | |
178 | static int __modify_user_hw_breakpoint(int pos, struct task_struct *tsk, | |
179 | struct hw_breakpoint *bp) | |
180 | { | |
181 | struct thread_struct *thread = &(tsk->thread); | |
182 | ||
183 | if ((pos >= hbp_kernel_pos) || (arch_validate_hwbkpt_settings(bp, tsk))) | |
184 | return -EINVAL; | |
185 | ||
186 | if (thread->hbp[pos] == NULL) | |
187 | return -EINVAL; | |
188 | ||
189 | thread->hbp[pos] = bp; | |
190 | /* | |
191 | * 'pos' must be that of a hbp register already used by 'tsk' | |
192 | * Otherwise arch_modify_user_hw_breakpoint() will fail | |
193 | */ | |
194 | arch_update_user_hw_breakpoint(pos, tsk); | |
195 | ||
196 | if (tsk == current) | |
197 | arch_install_thread_hw_breakpoint(tsk); | |
198 | ||
199 | return 0; | |
200 | } | |
201 | ||
202 | static void __unregister_user_hw_breakpoint(int pos, struct task_struct *tsk) | |
203 | { | |
204 | hbp_user_refcount[pos]--; | |
205 | tsk->thread.hbp[pos] = NULL; | |
206 | ||
207 | arch_update_user_hw_breakpoint(pos, tsk); | |
208 | ||
209 | if (tsk == current) | |
210 | arch_install_thread_hw_breakpoint(tsk); | |
211 | } | |
212 | ||
213 | /** | |
214 | * register_user_hw_breakpoint - register a hardware breakpoint for user space | |
215 | * @tsk: pointer to 'task_struct' of the process to which the address belongs | |
216 | * @bp: the breakpoint structure to register | |
217 | * | |
218 | * @bp.info->name or @bp.info->address, @bp.info->len, @bp.info->type and | |
219 | * @bp->triggered must be set properly before invocation | |
220 | * | |
221 | */ | |
222 | int register_user_hw_breakpoint(struct task_struct *tsk, | |
223 | struct hw_breakpoint *bp) | |
224 | { | |
225 | struct thread_struct *thread = &(tsk->thread); | |
226 | int i, rc = -ENOSPC; | |
227 | ||
228 | spin_lock_bh(&hw_breakpoint_lock); | |
229 | ||
230 | for (i = 0; i < hbp_kernel_pos; i++) { | |
231 | if (!thread->hbp[i]) { | |
232 | rc = __register_user_hw_breakpoint(i, tsk, bp); | |
233 | break; | |
234 | } | |
235 | } | |
236 | if (!rc) | |
237 | set_tsk_thread_flag(tsk, TIF_DEBUG); | |
238 | ||
239 | spin_unlock_bh(&hw_breakpoint_lock); | |
240 | return rc; | |
241 | } | |
242 | EXPORT_SYMBOL_GPL(register_user_hw_breakpoint); | |
243 | ||
244 | /** | |
245 | * modify_user_hw_breakpoint - modify a user-space hardware breakpoint | |
246 | * @tsk: pointer to 'task_struct' of the process to which the address belongs | |
247 | * @bp: the breakpoint structure to unregister | |
248 | * | |
249 | */ | |
250 | int modify_user_hw_breakpoint(struct task_struct *tsk, struct hw_breakpoint *bp) | |
251 | { | |
252 | struct thread_struct *thread = &(tsk->thread); | |
253 | int i, ret = -ENOENT; | |
254 | ||
255 | spin_lock_bh(&hw_breakpoint_lock); | |
256 | for (i = 0; i < hbp_kernel_pos; i++) { | |
257 | if (bp == thread->hbp[i]) { | |
258 | ret = __modify_user_hw_breakpoint(i, tsk, bp); | |
259 | break; | |
260 | } | |
261 | } | |
262 | spin_unlock_bh(&hw_breakpoint_lock); | |
263 | return ret; | |
264 | } | |
265 | EXPORT_SYMBOL_GPL(modify_user_hw_breakpoint); | |
266 | ||
267 | /** | |
268 | * unregister_user_hw_breakpoint - unregister a user-space hardware breakpoint | |
269 | * @tsk: pointer to 'task_struct' of the process to which the address belongs | |
270 | * @bp: the breakpoint structure to unregister | |
271 | * | |
272 | */ | |
273 | void unregister_user_hw_breakpoint(struct task_struct *tsk, | |
274 | struct hw_breakpoint *bp) | |
275 | { | |
276 | struct thread_struct *thread = &(tsk->thread); | |
277 | int i, pos = -1, hbp_counter = 0; | |
278 | ||
279 | spin_lock_bh(&hw_breakpoint_lock); | |
280 | for (i = 0; i < hbp_kernel_pos; i++) { | |
281 | if (thread->hbp[i]) | |
282 | hbp_counter++; | |
283 | if (bp == thread->hbp[i]) | |
284 | pos = i; | |
285 | } | |
286 | if (pos >= 0) { | |
287 | __unregister_user_hw_breakpoint(pos, tsk); | |
288 | hbp_counter--; | |
289 | } | |
290 | if (!hbp_counter) | |
291 | clear_tsk_thread_flag(tsk, TIF_DEBUG); | |
292 | ||
293 | spin_unlock_bh(&hw_breakpoint_lock); | |
294 | } | |
295 | EXPORT_SYMBOL_GPL(unregister_user_hw_breakpoint); | |
296 | ||
297 | /** | |
298 | * register_kernel_hw_breakpoint - register a hardware breakpoint for kernel space | |
299 | * @bp: the breakpoint structure to register | |
300 | * | |
301 | * @bp.info->name or @bp.info->address, @bp.info->len, @bp.info->type and | |
302 | * @bp->triggered must be set properly before invocation | |
303 | * | |
304 | */ | |
305 | int register_kernel_hw_breakpoint(struct hw_breakpoint *bp) | |
306 | { | |
307 | int rc; | |
308 | ||
309 | rc = arch_validate_hwbkpt_settings(bp, NULL); | |
310 | if (rc) | |
311 | return rc; | |
312 | ||
313 | spin_lock_bh(&hw_breakpoint_lock); | |
314 | ||
315 | rc = -ENOSPC; | |
316 | /* Check if we are over-committing */ | |
317 | if ((hbp_kernel_pos > 0) && (!hbp_user_refcount[hbp_kernel_pos-1])) { | |
318 | hbp_kernel_pos--; | |
319 | hbp_kernel[hbp_kernel_pos] = bp; | |
320 | on_each_cpu(arch_update_kernel_hw_breakpoint, NULL, 1); | |
321 | rc = 0; | |
322 | } | |
323 | ||
324 | spin_unlock_bh(&hw_breakpoint_lock); | |
325 | return rc; | |
326 | } | |
327 | EXPORT_SYMBOL_GPL(register_kernel_hw_breakpoint); | |
328 | ||
329 | /** | |
330 | * unregister_kernel_hw_breakpoint - unregister a HW breakpoint for kernel space | |
331 | * @bp: the breakpoint structure to unregister | |
332 | * | |
333 | * Uninstalls and unregisters @bp. | |
334 | */ | |
335 | void unregister_kernel_hw_breakpoint(struct hw_breakpoint *bp) | |
336 | { | |
337 | int i, j; | |
338 | ||
339 | spin_lock_bh(&hw_breakpoint_lock); | |
340 | ||
341 | /* Find the 'bp' in our list of breakpoints for kernel */ | |
342 | for (i = hbp_kernel_pos; i < HBP_NUM; i++) | |
343 | if (bp == hbp_kernel[i]) | |
344 | break; | |
345 | ||
346 | /* Check if we did not find a match for 'bp'. If so return early */ | |
347 | if (i == HBP_NUM) { | |
348 | spin_unlock_bh(&hw_breakpoint_lock); | |
349 | return; | |
350 | } | |
351 | ||
352 | /* | |
353 | * We'll shift the breakpoints one-level above to compact if | |
354 | * unregistration creates a hole | |
355 | */ | |
356 | for (j = i; j > hbp_kernel_pos; j--) | |
357 | hbp_kernel[j] = hbp_kernel[j-1]; | |
358 | ||
359 | hbp_kernel[hbp_kernel_pos] = NULL; | |
360 | on_each_cpu(arch_update_kernel_hw_breakpoint, NULL, 1); | |
361 | hbp_kernel_pos++; | |
362 | ||
363 | spin_unlock_bh(&hw_breakpoint_lock); | |
364 | } | |
365 | EXPORT_SYMBOL_GPL(unregister_kernel_hw_breakpoint); | |
366 | ||
367 | static struct notifier_block hw_breakpoint_exceptions_nb = { | |
368 | .notifier_call = hw_breakpoint_exceptions_notify, | |
369 | /* we need to be notified first */ | |
370 | .priority = 0x7fffffff | |
371 | }; | |
372 | ||
373 | static int __init init_hw_breakpoint(void) | |
374 | { | |
375 | return register_die_notifier(&hw_breakpoint_exceptions_nb); | |
376 | } | |
377 | ||
378 | core_initcall(init_hw_breakpoint); |