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_unsigned_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 write_sysreg(mdscr, mdscr_el1);
50 local_dbg_restore(flags);
52 NOKPROBE_SYMBOL(mdscr_write);
54 static u32 mdscr_read(void)
56 return read_sysreg(mdscr_el1);
58 NOKPROBE_SYMBOL(mdscr_read);
61 * Allow root to disable self-hosted debug from userspace.
62 * This is useful if you want to connect an external JTAG debugger.
64 static bool debug_enabled = true;
66 static int create_debug_debugfs_entry(void)
68 debugfs_create_bool("debug_enabled", 0644, NULL, &debug_enabled);
71 fs_initcall(create_debug_debugfs_entry);
73 static int __init early_debug_disable(char *buf)
75 debug_enabled = false;
79 early_param("nodebugmon", early_debug_disable);
82 * Keep track of debug users on each core.
83 * The ref counts are per-cpu so we use a local_t type.
85 static DEFINE_PER_CPU(int, mde_ref_count);
86 static DEFINE_PER_CPU(int, kde_ref_count);
88 void enable_debug_monitors(enum dbg_active_el el)
90 u32 mdscr, enable = 0;
92 WARN_ON(preemptible());
94 if (this_cpu_inc_return(mde_ref_count) == 1)
95 enable = DBG_MDSCR_MDE;
97 if (el == DBG_ACTIVE_EL1 &&
98 this_cpu_inc_return(kde_ref_count) == 1)
99 enable |= DBG_MDSCR_KDE;
101 if (enable && debug_enabled) {
102 mdscr = mdscr_read();
107 NOKPROBE_SYMBOL(enable_debug_monitors);
109 void disable_debug_monitors(enum dbg_active_el el)
111 u32 mdscr, disable = 0;
113 WARN_ON(preemptible());
115 if (this_cpu_dec_return(mde_ref_count) == 0)
116 disable = ~DBG_MDSCR_MDE;
118 if (el == DBG_ACTIVE_EL1 &&
119 this_cpu_dec_return(kde_ref_count) == 0)
120 disable &= ~DBG_MDSCR_KDE;
123 mdscr = mdscr_read();
128 NOKPROBE_SYMBOL(disable_debug_monitors);
133 static int clear_os_lock(unsigned int cpu)
135 write_sysreg(0, oslar_el1);
140 static int debug_monitors_init(void)
142 return cpuhp_setup_state(CPUHP_AP_ARM64_DEBUG_MONITORS_STARTING,
143 "arm64/debug_monitors:starting",
144 clear_os_lock, NULL);
146 postcore_initcall(debug_monitors_init);
149 * Single step API and exception handling.
151 static void set_regs_spsr_ss(struct pt_regs *regs)
153 regs->pstate |= DBG_SPSR_SS;
155 NOKPROBE_SYMBOL(set_regs_spsr_ss);
157 static void clear_regs_spsr_ss(struct pt_regs *regs)
159 regs->pstate &= ~DBG_SPSR_SS;
161 NOKPROBE_SYMBOL(clear_regs_spsr_ss);
163 /* EL1 Single Step Handler hooks */
164 static LIST_HEAD(step_hook);
165 static DEFINE_SPINLOCK(step_hook_lock);
167 void register_step_hook(struct step_hook *hook)
169 spin_lock(&step_hook_lock);
170 list_add_rcu(&hook->node, &step_hook);
171 spin_unlock(&step_hook_lock);
174 void unregister_step_hook(struct step_hook *hook)
176 spin_lock(&step_hook_lock);
177 list_del_rcu(&hook->node);
178 spin_unlock(&step_hook_lock);
183 * Call registered single step handlers
184 * There is no Syndrome info to check for determining the handler.
185 * So we call all the registered handlers, until the right handler is
186 * found which returns zero.
188 static int call_step_hook(struct pt_regs *regs, unsigned int esr)
190 struct step_hook *hook;
191 int retval = DBG_HOOK_ERROR;
195 list_for_each_entry_rcu(hook, &step_hook, node) {
196 retval = hook->fn(regs, esr);
197 if (retval == DBG_HOOK_HANDLED)
205 NOKPROBE_SYMBOL(call_step_hook);
207 static void send_user_sigtrap(int si_code)
209 struct pt_regs *regs = current_pt_regs();
214 .si_addr = (void __user *)instruction_pointer(regs),
217 if (WARN_ON(!user_mode(regs)))
220 if (interrupts_enabled(regs))
223 force_sig_info(SIGTRAP, &info, current);
226 static int single_step_handler(unsigned long addr, unsigned int esr,
227 struct pt_regs *regs)
229 bool handler_found = false;
232 * If we are stepping a pending breakpoint, call the hw_breakpoint
235 if (!reinstall_suspended_bps(regs))
238 #ifdef CONFIG_KPROBES
239 if (kprobe_single_step_handler(regs, esr) == DBG_HOOK_HANDLED)
240 handler_found = true;
242 if (!handler_found && call_step_hook(regs, esr) == DBG_HOOK_HANDLED)
243 handler_found = true;
245 if (!handler_found && user_mode(regs)) {
246 send_user_sigtrap(TRAP_TRACE);
249 * ptrace will disable single step unless explicitly
250 * asked to re-enable it. For other clients, it makes
251 * sense to leave it enabled (i.e. rewind the controls
252 * to the active-not-pending state).
254 user_rewind_single_step(current);
255 } else if (!handler_found) {
256 pr_warn("Unexpected kernel single-step exception at EL1\n");
258 * Re-enable stepping since we know that we will be
261 set_regs_spsr_ss(regs);
266 NOKPROBE_SYMBOL(single_step_handler);
269 * Breakpoint handler is re-entrant as another breakpoint can
270 * hit within breakpoint handler, especically in kprobes.
271 * Use reader/writer locks instead of plain spinlock.
273 static LIST_HEAD(break_hook);
274 static DEFINE_SPINLOCK(break_hook_lock);
276 void register_break_hook(struct break_hook *hook)
278 spin_lock(&break_hook_lock);
279 list_add_rcu(&hook->node, &break_hook);
280 spin_unlock(&break_hook_lock);
283 void unregister_break_hook(struct break_hook *hook)
285 spin_lock(&break_hook_lock);
286 list_del_rcu(&hook->node);
287 spin_unlock(&break_hook_lock);
291 static int call_break_hook(struct pt_regs *regs, unsigned int esr)
293 struct break_hook *hook;
294 int (*fn)(struct pt_regs *regs, unsigned int esr) = NULL;
297 list_for_each_entry_rcu(hook, &break_hook, node)
298 if ((esr & hook->esr_mask) == hook->esr_val)
302 return fn ? fn(regs, esr) : DBG_HOOK_ERROR;
304 NOKPROBE_SYMBOL(call_break_hook);
306 static int brk_handler(unsigned long addr, unsigned int esr,
307 struct pt_regs *regs)
309 bool handler_found = false;
311 #ifdef CONFIG_KPROBES
312 if ((esr & BRK64_ESR_MASK) == BRK64_ESR_KPROBES) {
313 if (kprobe_breakpoint_handler(regs, esr) == DBG_HOOK_HANDLED)
314 handler_found = true;
317 if (!handler_found && call_break_hook(regs, esr) == DBG_HOOK_HANDLED)
318 handler_found = true;
320 if (!handler_found && user_mode(regs)) {
321 send_user_sigtrap(TRAP_BRKPT);
322 } else if (!handler_found) {
323 pr_warn("Unexpected kernel BRK exception at EL1\n");
329 NOKPROBE_SYMBOL(brk_handler);
331 int aarch32_break_handler(struct pt_regs *regs)
336 void __user *pc = (void __user *)instruction_pointer(regs);
338 if (!compat_user_mode(regs))
341 if (compat_thumb_mode(regs)) {
342 /* get 16-bit Thumb instruction */
343 get_user(thumb_instr, (u16 __user *)pc);
344 thumb_instr = le16_to_cpu(thumb_instr);
345 if (thumb_instr == AARCH32_BREAK_THUMB2_LO) {
346 /* get second half of 32-bit Thumb-2 instruction */
347 get_user(thumb_instr, (u16 __user *)(pc + 2));
348 thumb_instr = le16_to_cpu(thumb_instr);
349 bp = thumb_instr == AARCH32_BREAK_THUMB2_HI;
351 bp = thumb_instr == AARCH32_BREAK_THUMB;
354 /* 32-bit ARM instruction */
355 get_user(arm_instr, (u32 __user *)pc);
356 arm_instr = le32_to_cpu(arm_instr);
357 bp = (arm_instr & ~0xf0000000) == AARCH32_BREAK_ARM;
363 send_user_sigtrap(TRAP_BRKPT);
366 NOKPROBE_SYMBOL(aarch32_break_handler);
368 static int __init debug_traps_init(void)
370 hook_debug_fault_code(DBG_ESR_EVT_HWSS, single_step_handler, SIGTRAP,
371 TRAP_TRACE, "single-step handler");
372 hook_debug_fault_code(DBG_ESR_EVT_BRK, brk_handler, SIGTRAP,
373 TRAP_BRKPT, "ptrace BRK handler");
376 arch_initcall(debug_traps_init);
378 /* Re-enable single step for syscall restarting. */
379 void user_rewind_single_step(struct task_struct *task)
382 * If single step is active for this thread, then set SPSR.SS
383 * to 1 to avoid returning to the active-pending state.
385 if (test_ti_thread_flag(task_thread_info(task), TIF_SINGLESTEP))
386 set_regs_spsr_ss(task_pt_regs(task));
388 NOKPROBE_SYMBOL(user_rewind_single_step);
390 void user_fastforward_single_step(struct task_struct *task)
392 if (test_ti_thread_flag(task_thread_info(task), TIF_SINGLESTEP))
393 clear_regs_spsr_ss(task_pt_regs(task));
397 void kernel_enable_single_step(struct pt_regs *regs)
399 WARN_ON(!irqs_disabled());
400 set_regs_spsr_ss(regs);
401 mdscr_write(mdscr_read() | DBG_MDSCR_SS);
402 enable_debug_monitors(DBG_ACTIVE_EL1);
404 NOKPROBE_SYMBOL(kernel_enable_single_step);
406 void kernel_disable_single_step(void)
408 WARN_ON(!irqs_disabled());
409 mdscr_write(mdscr_read() & ~DBG_MDSCR_SS);
410 disable_debug_monitors(DBG_ACTIVE_EL1);
412 NOKPROBE_SYMBOL(kernel_disable_single_step);
414 int kernel_active_single_step(void)
416 WARN_ON(!irqs_disabled());
417 return mdscr_read() & DBG_MDSCR_SS;
419 NOKPROBE_SYMBOL(kernel_active_single_step);
422 void user_enable_single_step(struct task_struct *task)
424 struct thread_info *ti = task_thread_info(task);
426 if (!test_and_set_ti_thread_flag(ti, TIF_SINGLESTEP))
427 set_regs_spsr_ss(task_pt_regs(task));
429 NOKPROBE_SYMBOL(user_enable_single_step);
431 void user_disable_single_step(struct task_struct *task)
433 clear_ti_thread_flag(task_thread_info(task), TIF_SINGLESTEP);
435 NOKPROBE_SYMBOL(user_disable_single_step);