K.Prasad | 62a038d | 2009-06-01 23:43:33 +0530 | [diff] [blame^] | 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); |