2 * ARMv8 single-step debug support and mdscr context switching.
4 * Copyright (C) 2012 ARM Limited
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.
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.
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/>.
18 * Author: Will Deacon <will.deacon@arm.com>
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/kprobes.h>
27 #include <linux/stat.h>
28 #include <linux/uaccess.h>
30 #include <asm/cpufeature.h>
31 #include <asm/cputype.h>
32 #include <asm/debug-monitors.h>
33 #include <asm/system_misc.h>
35 /* Determine debug architecture. */
36 u8 debug_monitors_arch(void)
38 return cpuid_feature_extract_field(read_system_reg(SYS_ID_AA64DFR0_EL1),
39 ID_AA64DFR0_DEBUGVER_SHIFT);
43 * MDSCR access routines.
45 static void mdscr_write(u32 mdscr)
48 local_dbg_save(flags);
49 asm volatile("msr mdscr_el1, %0" :: "r" (mdscr));
50 local_dbg_restore(flags);
52 NOKPROBE_SYMBOL(mdscr_write);
54 static u32 mdscr_read(void)
57 asm volatile("mrs %0, mdscr_el1" : "=r" (mdscr));
60 NOKPROBE_SYMBOL(mdscr_read);
63 * Allow root to disable self-hosted debug from userspace.
64 * This is useful if you want to connect an external JTAG debugger.
66 static bool debug_enabled = true;
68 static int create_debug_debugfs_entry(void)
70 debugfs_create_bool("debug_enabled", 0644, NULL, &debug_enabled);
73 fs_initcall(create_debug_debugfs_entry);
75 static int __init early_debug_disable(char *buf)
77 debug_enabled = false;
81 early_param("nodebugmon", early_debug_disable);
84 * Keep track of debug users on each core.
85 * The ref counts are per-cpu so we use a local_t type.
87 static DEFINE_PER_CPU(int, mde_ref_count);
88 static DEFINE_PER_CPU(int, kde_ref_count);
90 void enable_debug_monitors(enum dbg_active_el el)
92 u32 mdscr, enable = 0;
94 WARN_ON(preemptible());
96 if (this_cpu_inc_return(mde_ref_count) == 1)
97 enable = DBG_MDSCR_MDE;
99 if (el == DBG_ACTIVE_EL1 &&
100 this_cpu_inc_return(kde_ref_count) == 1)
101 enable |= DBG_MDSCR_KDE;
103 if (enable && debug_enabled) {
104 mdscr = mdscr_read();
109 NOKPROBE_SYMBOL(enable_debug_monitors);
111 void disable_debug_monitors(enum dbg_active_el el)
113 u32 mdscr, disable = 0;
115 WARN_ON(preemptible());
117 if (this_cpu_dec_return(mde_ref_count) == 0)
118 disable = ~DBG_MDSCR_MDE;
120 if (el == DBG_ACTIVE_EL1 &&
121 this_cpu_dec_return(kde_ref_count) == 0)
122 disable &= ~DBG_MDSCR_KDE;
125 mdscr = mdscr_read();
130 NOKPROBE_SYMBOL(disable_debug_monitors);
135 static void clear_os_lock(void *unused)
137 asm volatile("msr oslar_el1, %0" : : "r" (0));
140 static int os_lock_notify(struct notifier_block *self,
141 unsigned long action, void *data)
143 int cpu = (unsigned long)data;
144 if ((action & ~CPU_TASKS_FROZEN) == CPU_ONLINE)
145 smp_call_function_single(cpu, clear_os_lock, NULL, 1);
149 static struct notifier_block os_lock_nb = {
150 .notifier_call = os_lock_notify,
153 static int debug_monitors_init(void)
155 cpu_notifier_register_begin();
157 /* Clear the OS lock. */
158 on_each_cpu(clear_os_lock, NULL, 1);
161 /* Register hotplug handler. */
162 __register_cpu_notifier(&os_lock_nb);
164 cpu_notifier_register_done();
167 postcore_initcall(debug_monitors_init);
170 * Single step API and exception handling.
172 static void set_regs_spsr_ss(struct pt_regs *regs)
177 spsr &= ~DBG_SPSR_SS;
181 NOKPROBE_SYMBOL(set_regs_spsr_ss);
183 static void clear_regs_spsr_ss(struct pt_regs *regs)
188 spsr &= ~DBG_SPSR_SS;
191 NOKPROBE_SYMBOL(clear_regs_spsr_ss);
193 /* EL1 Single Step Handler hooks */
194 static LIST_HEAD(step_hook);
195 static DEFINE_SPINLOCK(step_hook_lock);
197 void register_step_hook(struct step_hook *hook)
199 spin_lock(&step_hook_lock);
200 list_add_rcu(&hook->node, &step_hook);
201 spin_unlock(&step_hook_lock);
204 void unregister_step_hook(struct step_hook *hook)
206 spin_lock(&step_hook_lock);
207 list_del_rcu(&hook->node);
208 spin_unlock(&step_hook_lock);
213 * Call registered single step handlers
214 * There is no Syndrome info to check for determining the handler.
215 * So we call all the registered handlers, until the right handler is
216 * found which returns zero.
218 static int call_step_hook(struct pt_regs *regs, unsigned int esr)
220 struct step_hook *hook;
221 int retval = DBG_HOOK_ERROR;
225 list_for_each_entry_rcu(hook, &step_hook, node) {
226 retval = hook->fn(regs, esr);
227 if (retval == DBG_HOOK_HANDLED)
235 NOKPROBE_SYMBOL(call_step_hook);
237 static int single_step_handler(unsigned long addr, unsigned int esr,
238 struct pt_regs *regs)
243 * If we are stepping a pending breakpoint, call the hw_breakpoint
246 if (!reinstall_suspended_bps(regs))
249 if (user_mode(regs)) {
250 info.si_signo = SIGTRAP;
252 info.si_code = TRAP_HWBKPT;
253 info.si_addr = (void __user *)instruction_pointer(regs);
254 force_sig_info(SIGTRAP, &info, current);
257 * ptrace will disable single step unless explicitly
258 * asked to re-enable it. For other clients, it makes
259 * sense to leave it enabled (i.e. rewind the controls
260 * to the active-not-pending state).
262 user_rewind_single_step(current);
264 #ifdef CONFIG_KPROBES
265 if (kprobe_single_step_handler(regs, esr) == DBG_HOOK_HANDLED)
268 if (call_step_hook(regs, esr) == DBG_HOOK_HANDLED)
271 pr_warning("Unexpected kernel single-step exception at EL1\n");
273 * Re-enable stepping since we know that we will be
276 set_regs_spsr_ss(regs);
281 NOKPROBE_SYMBOL(single_step_handler);
284 * Breakpoint handler is re-entrant as another breakpoint can
285 * hit within breakpoint handler, especically in kprobes.
286 * Use reader/writer locks instead of plain spinlock.
288 static LIST_HEAD(break_hook);
289 static DEFINE_SPINLOCK(break_hook_lock);
291 void register_break_hook(struct break_hook *hook)
293 spin_lock(&break_hook_lock);
294 list_add_rcu(&hook->node, &break_hook);
295 spin_unlock(&break_hook_lock);
298 void unregister_break_hook(struct break_hook *hook)
300 spin_lock(&break_hook_lock);
301 list_del_rcu(&hook->node);
302 spin_unlock(&break_hook_lock);
306 static int call_break_hook(struct pt_regs *regs, unsigned int esr)
308 struct break_hook *hook;
309 int (*fn)(struct pt_regs *regs, unsigned int esr) = NULL;
312 list_for_each_entry_rcu(hook, &break_hook, node)
313 if ((esr & hook->esr_mask) == hook->esr_val)
317 return fn ? fn(regs, esr) : DBG_HOOK_ERROR;
319 NOKPROBE_SYMBOL(call_break_hook);
321 static int brk_handler(unsigned long addr, unsigned int esr,
322 struct pt_regs *regs)
326 if (user_mode(regs)) {
330 .si_code = TRAP_BRKPT,
331 .si_addr = (void __user *)instruction_pointer(regs),
334 force_sig_info(SIGTRAP, &info, current);
336 #ifdef CONFIG_KPROBES
337 else if ((esr & BRK64_ESR_MASK) == BRK64_ESR_KPROBES) {
338 if (kprobe_breakpoint_handler(regs, esr) != DBG_HOOK_HANDLED)
342 else if (call_break_hook(regs, esr) != DBG_HOOK_HANDLED) {
343 pr_warn("Unexpected kernel BRK exception at EL1\n");
349 NOKPROBE_SYMBOL(brk_handler);
351 int aarch32_break_handler(struct pt_regs *regs)
357 void __user *pc = (void __user *)instruction_pointer(regs);
359 if (!compat_user_mode(regs))
362 if (compat_thumb_mode(regs)) {
363 /* get 16-bit Thumb instruction */
364 get_user(thumb_instr, (u16 __user *)pc);
365 thumb_instr = le16_to_cpu(thumb_instr);
366 if (thumb_instr == AARCH32_BREAK_THUMB2_LO) {
367 /* get second half of 32-bit Thumb-2 instruction */
368 get_user(thumb_instr, (u16 __user *)(pc + 2));
369 thumb_instr = le16_to_cpu(thumb_instr);
370 bp = thumb_instr == AARCH32_BREAK_THUMB2_HI;
372 bp = thumb_instr == AARCH32_BREAK_THUMB;
375 /* 32-bit ARM instruction */
376 get_user(arm_instr, (u32 __user *)pc);
377 arm_instr = le32_to_cpu(arm_instr);
378 bp = (arm_instr & ~0xf0000000) == AARCH32_BREAK_ARM;
387 .si_code = TRAP_BRKPT,
391 force_sig_info(SIGTRAP, &info, current);
394 NOKPROBE_SYMBOL(aarch32_break_handler);
396 static int __init debug_traps_init(void)
398 hook_debug_fault_code(DBG_ESR_EVT_HWSS, single_step_handler, SIGTRAP,
399 TRAP_HWBKPT, "single-step handler");
400 hook_debug_fault_code(DBG_ESR_EVT_BRK, brk_handler, SIGTRAP,
401 TRAP_BRKPT, "ptrace BRK handler");
404 arch_initcall(debug_traps_init);
406 /* Re-enable single step for syscall restarting. */
407 void user_rewind_single_step(struct task_struct *task)
410 * If single step is active for this thread, then set SPSR.SS
411 * to 1 to avoid returning to the active-pending state.
413 if (test_ti_thread_flag(task_thread_info(task), TIF_SINGLESTEP))
414 set_regs_spsr_ss(task_pt_regs(task));
416 NOKPROBE_SYMBOL(user_rewind_single_step);
418 void user_fastforward_single_step(struct task_struct *task)
420 if (test_ti_thread_flag(task_thread_info(task), TIF_SINGLESTEP))
421 clear_regs_spsr_ss(task_pt_regs(task));
425 void kernel_enable_single_step(struct pt_regs *regs)
427 WARN_ON(!irqs_disabled());
428 set_regs_spsr_ss(regs);
429 mdscr_write(mdscr_read() | DBG_MDSCR_SS);
430 enable_debug_monitors(DBG_ACTIVE_EL1);
432 NOKPROBE_SYMBOL(kernel_enable_single_step);
434 void kernel_disable_single_step(void)
436 WARN_ON(!irqs_disabled());
437 mdscr_write(mdscr_read() & ~DBG_MDSCR_SS);
438 disable_debug_monitors(DBG_ACTIVE_EL1);
440 NOKPROBE_SYMBOL(kernel_disable_single_step);
442 int kernel_active_single_step(void)
444 WARN_ON(!irqs_disabled());
445 return mdscr_read() & DBG_MDSCR_SS;
447 NOKPROBE_SYMBOL(kernel_active_single_step);
450 void user_enable_single_step(struct task_struct *task)
452 struct thread_info *ti = task_thread_info(task);
454 if (!test_and_set_ti_thread_flag(ti, TIF_SINGLESTEP))
455 set_regs_spsr_ss(task_pt_regs(task));
457 NOKPROBE_SYMBOL(user_enable_single_step);
459 void user_disable_single_step(struct task_struct *task)
461 clear_ti_thread_flag(task_thread_info(task), TIF_SINGLESTEP);
463 NOKPROBE_SYMBOL(user_disable_single_step);