1 /*
2 * ARMv8 single-step debug support and mdscr context switching.
3 *
4 * Copyright (C) 2012 ARM Limited
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 version 2 as
8 * published by the Free Software Foundation.
9 *
10 * This program is distributed in the hope that it will be useful,
11 * but WITHOUT ANY WARRANTY; without even the implied warranty of
12 * MERCHANTABILITY or FITNESS FOR A PARTICULAR PURPOSE. See the
13 * GNU General Public License for more details.
14 *
15 * You should have received a copy of the GNU General Public License
16 * along with this program. If not, see <http://www.gnu.org/licenses/>.
17 *
18 * Author: Will Deacon <will.deacon@arm.com>
19 */
20
21 #include <linux/cpu.h>
22 #include <linux/debugfs.h>
23 #include <linux/hardirq.h>
24 #include <linux/init.h>
25 #include <linux/ptrace.h>
26 #include <linux/stat.h>
27 #include <linux/uaccess.h>
28
29 #include <asm/debug-monitors.h>
30 #include <asm/cputype.h>
31 #include <asm/system_misc.h>
32
33 /* Determine debug architecture. */
debug_monitors_arch(void)34 u8 debug_monitors_arch(void)
35 {
36 return read_cpuid(ID_AA64DFR0_EL1) & 0xf;
37 }
38
39 /*
40 * MDSCR access routines.
41 */
mdscr_write(u32 mdscr)42 static void mdscr_write(u32 mdscr)
43 {
44 unsigned long flags;
45 local_dbg_save(flags);
46 asm volatile("msr mdscr_el1, %0" :: "r" (mdscr));
47 local_dbg_restore(flags);
48 }
49
mdscr_read(void)50 static u32 mdscr_read(void)
51 {
52 u32 mdscr;
53 asm volatile("mrs %0, mdscr_el1" : "=r" (mdscr));
54 return mdscr;
55 }
56
57 /*
58 * Allow root to disable self-hosted debug from userspace.
59 * This is useful if you want to connect an external JTAG debugger.
60 */
61 static u32 debug_enabled = 1;
62
create_debug_debugfs_entry(void)63 static int create_debug_debugfs_entry(void)
64 {
65 debugfs_create_bool("debug_enabled", 0644, NULL, &debug_enabled);
66 return 0;
67 }
68 fs_initcall(create_debug_debugfs_entry);
69
early_debug_disable(char * buf)70 static int __init early_debug_disable(char *buf)
71 {
72 debug_enabled = 0;
73 return 0;
74 }
75
76 early_param("nodebugmon", early_debug_disable);
77
78 /*
79 * Keep track of debug users on each core.
80 * The ref counts are per-cpu so we use a local_t type.
81 */
82 static DEFINE_PER_CPU(int, mde_ref_count);
83 static DEFINE_PER_CPU(int, kde_ref_count);
84
enable_debug_monitors(enum debug_el el)85 void enable_debug_monitors(enum debug_el el)
86 {
87 u32 mdscr, enable = 0;
88
89 WARN_ON(preemptible());
90
91 if (this_cpu_inc_return(mde_ref_count) == 1)
92 enable = DBG_MDSCR_MDE;
93
94 if (el == DBG_ACTIVE_EL1 &&
95 this_cpu_inc_return(kde_ref_count) == 1)
96 enable |= DBG_MDSCR_KDE;
97
98 if (enable && debug_enabled) {
99 mdscr = mdscr_read();
100 mdscr |= enable;
101 mdscr_write(mdscr);
102 }
103 }
104
disable_debug_monitors(enum debug_el el)105 void disable_debug_monitors(enum debug_el el)
106 {
107 u32 mdscr, disable = 0;
108
109 WARN_ON(preemptible());
110
111 if (this_cpu_dec_return(mde_ref_count) == 0)
112 disable = ~DBG_MDSCR_MDE;
113
114 if (el == DBG_ACTIVE_EL1 &&
115 this_cpu_dec_return(kde_ref_count) == 0)
116 disable &= ~DBG_MDSCR_KDE;
117
118 if (disable) {
119 mdscr = mdscr_read();
120 mdscr &= disable;
121 mdscr_write(mdscr);
122 }
123 }
124
125 /*
126 * OS lock clearing.
127 */
clear_os_lock(void * unused)128 static void clear_os_lock(void *unused)
129 {
130 asm volatile("msr oslar_el1, %0" : : "r" (0));
131 }
132
os_lock_notify(struct notifier_block * self,unsigned long action,void * data)133 static int os_lock_notify(struct notifier_block *self,
134 unsigned long action, void *data)
135 {
136 int cpu = (unsigned long)data;
137 if (action == CPU_ONLINE)
138 smp_call_function_single(cpu, clear_os_lock, NULL, 1);
139 return NOTIFY_OK;
140 }
141
142 static struct notifier_block os_lock_nb = {
143 .notifier_call = os_lock_notify,
144 };
145
debug_monitors_init(void)146 static int debug_monitors_init(void)
147 {
148 cpu_notifier_register_begin();
149
150 /* Clear the OS lock. */
151 on_each_cpu(clear_os_lock, NULL, 1);
152 isb();
153 local_dbg_enable();
154
155 /* Register hotplug handler. */
156 __register_cpu_notifier(&os_lock_nb);
157
158 cpu_notifier_register_done();
159 return 0;
160 }
161 postcore_initcall(debug_monitors_init);
162
163 /*
164 * Single step API and exception handling.
165 */
set_regs_spsr_ss(struct pt_regs * regs)166 static void set_regs_spsr_ss(struct pt_regs *regs)
167 {
168 unsigned long spsr;
169
170 spsr = regs->pstate;
171 spsr &= ~DBG_SPSR_SS;
172 spsr |= DBG_SPSR_SS;
173 regs->pstate = spsr;
174 }
175
clear_regs_spsr_ss(struct pt_regs * regs)176 static void clear_regs_spsr_ss(struct pt_regs *regs)
177 {
178 unsigned long spsr;
179
180 spsr = regs->pstate;
181 spsr &= ~DBG_SPSR_SS;
182 regs->pstate = spsr;
183 }
184
185 /* EL1 Single Step Handler hooks */
186 static LIST_HEAD(step_hook);
187 static DEFINE_SPINLOCK(step_hook_lock);
188
register_step_hook(struct step_hook * hook)189 void register_step_hook(struct step_hook *hook)
190 {
191 spin_lock(&step_hook_lock);
192 list_add_rcu(&hook->node, &step_hook);
193 spin_unlock(&step_hook_lock);
194 }
195
unregister_step_hook(struct step_hook * hook)196 void unregister_step_hook(struct step_hook *hook)
197 {
198 spin_lock(&step_hook_lock);
199 list_del_rcu(&hook->node);
200 spin_unlock(&step_hook_lock);
201 synchronize_rcu();
202 }
203
204 /*
205 * Call registered single step handers
206 * There is no Syndrome info to check for determining the handler.
207 * So we call all the registered handlers, until the right handler is
208 * found which returns zero.
209 */
call_step_hook(struct pt_regs * regs,unsigned int esr)210 static int call_step_hook(struct pt_regs *regs, unsigned int esr)
211 {
212 struct step_hook *hook;
213 int retval = DBG_HOOK_ERROR;
214
215 rcu_read_lock();
216
217 list_for_each_entry_rcu(hook, &step_hook, node) {
218 retval = hook->fn(regs, esr);
219 if (retval == DBG_HOOK_HANDLED)
220 break;
221 }
222
223 rcu_read_unlock();
224
225 return retval;
226 }
227
single_step_handler(unsigned long addr,unsigned int esr,struct pt_regs * regs)228 static int single_step_handler(unsigned long addr, unsigned int esr,
229 struct pt_regs *regs)
230 {
231 siginfo_t info;
232
233 /*
234 * If we are stepping a pending breakpoint, call the hw_breakpoint
235 * handler first.
236 */
237 if (!reinstall_suspended_bps(regs))
238 return 0;
239
240 if (user_mode(regs)) {
241 info.si_signo = SIGTRAP;
242 info.si_errno = 0;
243 info.si_code = TRAP_HWBKPT;
244 info.si_addr = (void __user *)instruction_pointer(regs);
245 force_sig_info(SIGTRAP, &info, current);
246
247 /*
248 * ptrace will disable single step unless explicitly
249 * asked to re-enable it. For other clients, it makes
250 * sense to leave it enabled (i.e. rewind the controls
251 * to the active-not-pending state).
252 */
253 user_rewind_single_step(current);
254 } else {
255 if (call_step_hook(regs, esr) == DBG_HOOK_HANDLED)
256 return 0;
257
258 pr_warning("Unexpected kernel single-step exception at EL1\n");
259 /*
260 * Re-enable stepping since we know that we will be
261 * returning to regs.
262 */
263 set_regs_spsr_ss(regs);
264 }
265
266 return 0;
267 }
268
269 /*
270 * Breakpoint handler is re-entrant as another breakpoint can
271 * hit within breakpoint handler, especically in kprobes.
272 * Use reader/writer locks instead of plain spinlock.
273 */
274 static LIST_HEAD(break_hook);
275 static DEFINE_SPINLOCK(break_hook_lock);
276
register_break_hook(struct break_hook * hook)277 void register_break_hook(struct break_hook *hook)
278 {
279 spin_lock(&break_hook_lock);
280 list_add_rcu(&hook->node, &break_hook);
281 spin_unlock(&break_hook_lock);
282 }
283
unregister_break_hook(struct break_hook * hook)284 void unregister_break_hook(struct break_hook *hook)
285 {
286 spin_lock(&break_hook_lock);
287 list_del_rcu(&hook->node);
288 spin_unlock(&break_hook_lock);
289 synchronize_rcu();
290 }
291
call_break_hook(struct pt_regs * regs,unsigned int esr)292 static int call_break_hook(struct pt_regs *regs, unsigned int esr)
293 {
294 struct break_hook *hook;
295 int (*fn)(struct pt_regs *regs, unsigned int esr) = NULL;
296
297 rcu_read_lock();
298 list_for_each_entry_rcu(hook, &break_hook, node)
299 if ((esr & hook->esr_mask) == hook->esr_val)
300 fn = hook->fn;
301 rcu_read_unlock();
302
303 return fn ? fn(regs, esr) : DBG_HOOK_ERROR;
304 }
305
brk_handler(unsigned long addr,unsigned int esr,struct pt_regs * regs)306 static int brk_handler(unsigned long addr, unsigned int esr,
307 struct pt_regs *regs)
308 {
309 siginfo_t info;
310
311 if (user_mode(regs)) {
312 info = (siginfo_t) {
313 .si_signo = SIGTRAP,
314 .si_errno = 0,
315 .si_code = TRAP_BRKPT,
316 .si_addr = (void __user *)instruction_pointer(regs),
317 };
318
319 force_sig_info(SIGTRAP, &info, current);
320 } else if (call_break_hook(regs, esr) != DBG_HOOK_HANDLED) {
321 pr_warning("Unexpected kernel BRK exception at EL1\n");
322 return -EFAULT;
323 }
324
325 return 0;
326 }
327
aarch32_break_handler(struct pt_regs * regs)328 int aarch32_break_handler(struct pt_regs *regs)
329 {
330 siginfo_t info;
331 u32 arm_instr;
332 u16 thumb_instr;
333 bool bp = false;
334 void __user *pc = (void __user *)instruction_pointer(regs);
335
336 if (!compat_user_mode(regs))
337 return -EFAULT;
338
339 if (compat_thumb_mode(regs)) {
340 /* get 16-bit Thumb instruction */
341 get_user(thumb_instr, (u16 __user *)pc);
342 thumb_instr = le16_to_cpu(thumb_instr);
343 if (thumb_instr == AARCH32_BREAK_THUMB2_LO) {
344 /* get second half of 32-bit Thumb-2 instruction */
345 get_user(thumb_instr, (u16 __user *)(pc + 2));
346 thumb_instr = le16_to_cpu(thumb_instr);
347 bp = thumb_instr == AARCH32_BREAK_THUMB2_HI;
348 } else {
349 bp = thumb_instr == AARCH32_BREAK_THUMB;
350 }
351 } else {
352 /* 32-bit ARM instruction */
353 get_user(arm_instr, (u32 __user *)pc);
354 arm_instr = le32_to_cpu(arm_instr);
355 bp = (arm_instr & ~0xf0000000) == AARCH32_BREAK_ARM;
356 }
357
358 if (!bp)
359 return -EFAULT;
360
361 info = (siginfo_t) {
362 .si_signo = SIGTRAP,
363 .si_errno = 0,
364 .si_code = TRAP_BRKPT,
365 .si_addr = pc,
366 };
367
368 force_sig_info(SIGTRAP, &info, current);
369 return 0;
370 }
371
debug_traps_init(void)372 static int __init debug_traps_init(void)
373 {
374 hook_debug_fault_code(DBG_ESR_EVT_HWSS, single_step_handler, SIGTRAP,
375 TRAP_HWBKPT, "single-step handler");
376 hook_debug_fault_code(DBG_ESR_EVT_BRK, brk_handler, SIGTRAP,
377 TRAP_BRKPT, "ptrace BRK handler");
378 return 0;
379 }
380 arch_initcall(debug_traps_init);
381
382 /* Re-enable single step for syscall restarting. */
user_rewind_single_step(struct task_struct * task)383 void user_rewind_single_step(struct task_struct *task)
384 {
385 /*
386 * If single step is active for this thread, then set SPSR.SS
387 * to 1 to avoid returning to the active-pending state.
388 */
389 if (test_ti_thread_flag(task_thread_info(task), TIF_SINGLESTEP))
390 set_regs_spsr_ss(task_pt_regs(task));
391 }
392
user_fastforward_single_step(struct task_struct * task)393 void user_fastforward_single_step(struct task_struct *task)
394 {
395 if (test_ti_thread_flag(task_thread_info(task), TIF_SINGLESTEP))
396 clear_regs_spsr_ss(task_pt_regs(task));
397 }
398
399 /* Kernel API */
kernel_enable_single_step(struct pt_regs * regs)400 void kernel_enable_single_step(struct pt_regs *regs)
401 {
402 WARN_ON(!irqs_disabled());
403 set_regs_spsr_ss(regs);
404 mdscr_write(mdscr_read() | DBG_MDSCR_SS);
405 enable_debug_monitors(DBG_ACTIVE_EL1);
406 }
407
kernel_disable_single_step(void)408 void kernel_disable_single_step(void)
409 {
410 WARN_ON(!irqs_disabled());
411 mdscr_write(mdscr_read() & ~DBG_MDSCR_SS);
412 disable_debug_monitors(DBG_ACTIVE_EL1);
413 }
414
kernel_active_single_step(void)415 int kernel_active_single_step(void)
416 {
417 WARN_ON(!irqs_disabled());
418 return mdscr_read() & DBG_MDSCR_SS;
419 }
420
421 /* ptrace API */
user_enable_single_step(struct task_struct * task)422 void user_enable_single_step(struct task_struct *task)
423 {
424 set_ti_thread_flag(task_thread_info(task), TIF_SINGLESTEP);
425 set_regs_spsr_ss(task_pt_regs(task));
426 }
427
user_disable_single_step(struct task_struct * task)428 void user_disable_single_step(struct task_struct *task)
429 {
430 clear_ti_thread_flag(task_thread_info(task), TIF_SINGLESTEP);
431 }
432