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>
29 #include <linux/sched/task_stack.h>
31 #include <asm/cpufeature.h>
32 #include <asm/cputype.h>
33 #include <asm/debug-monitors.h>
34 #include <asm/system_misc.h>
36 /* Determine debug architecture. */
37 u8 debug_monitors_arch(void)
39 return cpuid_feature_extract_unsigned_field(read_sanitised_ftr_reg(SYS_ID_AA64DFR0_EL1),
40 ID_AA64DFR0_DEBUGVER_SHIFT);
44 * MDSCR access routines.
46 static void mdscr_write(u32 mdscr)
49 local_dbg_save(flags);
50 write_sysreg(mdscr, mdscr_el1);
51 local_dbg_restore(flags);
53 NOKPROBE_SYMBOL(mdscr_write);
55 static u32 mdscr_read(void)
57 return read_sysreg(mdscr_el1);
59 NOKPROBE_SYMBOL(mdscr_read);
62 * Allow root to disable self-hosted debug from userspace.
63 * This is useful if you want to connect an external JTAG debugger.
65 static bool debug_enabled = true;
67 static int create_debug_debugfs_entry(void)
69 debugfs_create_bool("debug_enabled", 0644, NULL, &debug_enabled);
72 fs_initcall(create_debug_debugfs_entry);
74 static int __init early_debug_disable(char *buf)
76 debug_enabled = false;
80 early_param("nodebugmon", early_debug_disable);
83 * Keep track of debug users on each core.
84 * The ref counts are per-cpu so we use a local_t type.
86 static DEFINE_PER_CPU(int, mde_ref_count);
87 static DEFINE_PER_CPU(int, kde_ref_count);
89 void enable_debug_monitors(enum dbg_active_el el)
91 u32 mdscr, enable = 0;
93 WARN_ON(preemptible());
95 if (this_cpu_inc_return(mde_ref_count) == 1)
96 enable = DBG_MDSCR_MDE;
98 if (el == DBG_ACTIVE_EL1 &&
99 this_cpu_inc_return(kde_ref_count) == 1)
100 enable |= DBG_MDSCR_KDE;
102 if (enable && debug_enabled) {
103 mdscr = mdscr_read();
108 NOKPROBE_SYMBOL(enable_debug_monitors);
110 void disable_debug_monitors(enum dbg_active_el el)
112 u32 mdscr, disable = 0;
114 WARN_ON(preemptible());
116 if (this_cpu_dec_return(mde_ref_count) == 0)
117 disable = ~DBG_MDSCR_MDE;
119 if (el == DBG_ACTIVE_EL1 &&
120 this_cpu_dec_return(kde_ref_count) == 0)
121 disable &= ~DBG_MDSCR_KDE;
124 mdscr = mdscr_read();
129 NOKPROBE_SYMBOL(disable_debug_monitors);
134 static int clear_os_lock(unsigned int cpu)
136 write_sysreg(0, osdlr_el1);
137 write_sysreg(0, oslar_el1);
142 static int debug_monitors_init(void)
144 return cpuhp_setup_state(CPUHP_AP_ARM64_DEBUG_MONITORS_STARTING,
145 "arm64/debug_monitors:starting",
146 clear_os_lock, NULL);
148 postcore_initcall(debug_monitors_init);
151 * Single step API and exception handling.
153 static void set_user_regs_spsr_ss(struct user_pt_regs *regs)
155 regs->pstate |= DBG_SPSR_SS;
157 NOKPROBE_SYMBOL(set_user_regs_spsr_ss);
159 static void clear_user_regs_spsr_ss(struct user_pt_regs *regs)
161 regs->pstate &= ~DBG_SPSR_SS;
163 NOKPROBE_SYMBOL(clear_user_regs_spsr_ss);
165 #define set_regs_spsr_ss(r) set_user_regs_spsr_ss(&(r)->user_regs)
166 #define clear_regs_spsr_ss(r) clear_user_regs_spsr_ss(&(r)->user_regs)
168 /* EL1 Single Step Handler hooks */
169 static LIST_HEAD(step_hook);
170 static DEFINE_SPINLOCK(step_hook_lock);
172 void register_step_hook(struct step_hook *hook)
174 spin_lock(&step_hook_lock);
175 list_add_rcu(&hook->node, &step_hook);
176 spin_unlock(&step_hook_lock);
179 void unregister_step_hook(struct step_hook *hook)
181 spin_lock(&step_hook_lock);
182 list_del_rcu(&hook->node);
183 spin_unlock(&step_hook_lock);
188 * Call registered single step handlers
189 * There is no Syndrome info to check for determining the handler.
190 * So we call all the registered handlers, until the right handler is
191 * found which returns zero.
193 static int call_step_hook(struct pt_regs *regs, unsigned int esr)
195 struct step_hook *hook;
196 int retval = DBG_HOOK_ERROR;
200 list_for_each_entry_rcu(hook, &step_hook, node) {
201 retval = hook->fn(regs, esr);
202 if (retval == DBG_HOOK_HANDLED)
210 NOKPROBE_SYMBOL(call_step_hook);
212 static void send_user_sigtrap(int si_code)
214 struct pt_regs *regs = current_pt_regs();
219 .si_addr = (void __user *)instruction_pointer(regs),
222 if (WARN_ON(!user_mode(regs)))
225 if (interrupts_enabled(regs))
228 force_sig_info(SIGTRAP, &info, current);
231 static int single_step_handler(unsigned long addr, unsigned int esr,
232 struct pt_regs *regs)
234 bool handler_found = false;
237 * If we are stepping a pending breakpoint, call the hw_breakpoint
240 if (!reinstall_suspended_bps(regs))
243 #ifdef CONFIG_KPROBES
244 if (kprobe_single_step_handler(regs, esr) == DBG_HOOK_HANDLED)
245 handler_found = true;
247 if (!handler_found && call_step_hook(regs, esr) == DBG_HOOK_HANDLED)
248 handler_found = true;
250 if (!handler_found && user_mode(regs)) {
251 send_user_sigtrap(TRAP_TRACE);
254 * ptrace will disable single step unless explicitly
255 * asked to re-enable it. For other clients, it makes
256 * sense to leave it enabled (i.e. rewind the controls
257 * to the active-not-pending state).
259 user_rewind_single_step(current);
260 } else if (!handler_found) {
261 pr_warn("Unexpected kernel single-step exception at EL1\n");
263 * Re-enable stepping since we know that we will be
266 set_regs_spsr_ss(regs);
271 NOKPROBE_SYMBOL(single_step_handler);
274 * Breakpoint handler is re-entrant as another breakpoint can
275 * hit within breakpoint handler, especically in kprobes.
276 * Use reader/writer locks instead of plain spinlock.
278 static LIST_HEAD(break_hook);
279 static DEFINE_SPINLOCK(break_hook_lock);
281 void register_break_hook(struct break_hook *hook)
283 spin_lock(&break_hook_lock);
284 list_add_rcu(&hook->node, &break_hook);
285 spin_unlock(&break_hook_lock);
288 void unregister_break_hook(struct break_hook *hook)
290 spin_lock(&break_hook_lock);
291 list_del_rcu(&hook->node);
292 spin_unlock(&break_hook_lock);
296 static int call_break_hook(struct pt_regs *regs, unsigned int esr)
298 struct break_hook *hook;
299 int (*fn)(struct pt_regs *regs, unsigned int esr) = NULL;
302 list_for_each_entry_rcu(hook, &break_hook, node)
303 if ((esr & hook->esr_mask) == hook->esr_val)
307 return fn ? fn(regs, esr) : DBG_HOOK_ERROR;
309 NOKPROBE_SYMBOL(call_break_hook);
311 static int brk_handler(unsigned long addr, unsigned int esr,
312 struct pt_regs *regs)
314 bool handler_found = false;
316 #ifdef CONFIG_KPROBES
317 if ((esr & BRK64_ESR_MASK) == BRK64_ESR_KPROBES) {
318 if (kprobe_breakpoint_handler(regs, esr) == DBG_HOOK_HANDLED)
319 handler_found = true;
322 if (!handler_found && call_break_hook(regs, esr) == DBG_HOOK_HANDLED)
323 handler_found = true;
325 if (!handler_found && user_mode(regs)) {
326 send_user_sigtrap(TRAP_BRKPT);
327 } else if (!handler_found) {
328 pr_warn("Unexpected kernel BRK exception at EL1\n");
334 NOKPROBE_SYMBOL(brk_handler);
336 int aarch32_break_handler(struct pt_regs *regs)
341 void __user *pc = (void __user *)instruction_pointer(regs);
343 if (!compat_user_mode(regs))
346 if (compat_thumb_mode(regs)) {
347 /* get 16-bit Thumb instruction */
349 get_user(instr, (__le16 __user *)pc);
350 thumb_instr = le16_to_cpu(instr);
351 if (thumb_instr == AARCH32_BREAK_THUMB2_LO) {
352 /* get second half of 32-bit Thumb-2 instruction */
353 get_user(instr, (__le16 __user *)(pc + 2));
354 thumb_instr = le16_to_cpu(instr);
355 bp = thumb_instr == AARCH32_BREAK_THUMB2_HI;
357 bp = thumb_instr == AARCH32_BREAK_THUMB;
360 /* 32-bit ARM instruction */
362 get_user(instr, (__le32 __user *)pc);
363 arm_instr = le32_to_cpu(instr);
364 bp = (arm_instr & ~0xf0000000) == AARCH32_BREAK_ARM;
370 send_user_sigtrap(TRAP_BRKPT);
373 NOKPROBE_SYMBOL(aarch32_break_handler);
375 static int __init debug_traps_init(void)
377 hook_debug_fault_code(DBG_ESR_EVT_HWSS, single_step_handler, SIGTRAP,
378 TRAP_TRACE, "single-step handler");
379 hook_debug_fault_code(DBG_ESR_EVT_BRK, brk_handler, SIGTRAP,
380 TRAP_BRKPT, "ptrace BRK handler");
383 arch_initcall(debug_traps_init);
385 /* Re-enable single step for syscall restarting. */
386 void user_rewind_single_step(struct task_struct *task)
389 * If single step is active for this thread, then set SPSR.SS
390 * to 1 to avoid returning to the active-pending state.
392 if (test_tsk_thread_flag(task, TIF_SINGLESTEP))
393 set_regs_spsr_ss(task_pt_regs(task));
395 NOKPROBE_SYMBOL(user_rewind_single_step);
397 void user_fastforward_single_step(struct task_struct *task)
399 if (test_tsk_thread_flag(task, TIF_SINGLESTEP))
400 clear_regs_spsr_ss(task_pt_regs(task));
403 void user_regs_reset_single_step(struct user_pt_regs *regs,
404 struct task_struct *task)
406 if (test_tsk_thread_flag(task, TIF_SINGLESTEP))
407 set_user_regs_spsr_ss(regs);
409 clear_user_regs_spsr_ss(regs);
413 void kernel_enable_single_step(struct pt_regs *regs)
415 WARN_ON(!irqs_disabled());
416 set_regs_spsr_ss(regs);
417 mdscr_write(mdscr_read() | DBG_MDSCR_SS);
418 enable_debug_monitors(DBG_ACTIVE_EL1);
420 NOKPROBE_SYMBOL(kernel_enable_single_step);
422 void kernel_disable_single_step(void)
424 WARN_ON(!irqs_disabled());
425 mdscr_write(mdscr_read() & ~DBG_MDSCR_SS);
426 disable_debug_monitors(DBG_ACTIVE_EL1);
428 NOKPROBE_SYMBOL(kernel_disable_single_step);
430 int kernel_active_single_step(void)
432 WARN_ON(!irqs_disabled());
433 return mdscr_read() & DBG_MDSCR_SS;
435 NOKPROBE_SYMBOL(kernel_active_single_step);
437 void kernel_rewind_single_step(struct pt_regs *regs)
439 set_regs_spsr_ss(regs);
443 void user_enable_single_step(struct task_struct *task)
445 struct thread_info *ti = task_thread_info(task);
447 if (!test_and_set_ti_thread_flag(ti, TIF_SINGLESTEP))
448 set_regs_spsr_ss(task_pt_regs(task));
450 NOKPROBE_SYMBOL(user_enable_single_step);
452 void user_disable_single_step(struct task_struct *task)
454 clear_ti_thread_flag(task_thread_info(task), TIF_SINGLESTEP);
456 NOKPROBE_SYMBOL(user_disable_single_step);