1 // SPDX-License-Identifier: GPL-2.0-only
2 /*
3 * ARMv8 single-step debug support and mdscr context switching.
4 *
5 * Copyright (C) 2012 ARM Limited
6 *
7 * Author: Will Deacon <will.deacon@arm.com>
8 */
9
10 #include <linux/cpu.h>
11 #include <linux/debugfs.h>
12 #include <linux/hardirq.h>
13 #include <linux/init.h>
14 #include <linux/ptrace.h>
15 #include <linux/kprobes.h>
16 #include <linux/stat.h>
17 #include <linux/uaccess.h>
18 #include <linux/sched/task_stack.h>
19
20 #include <asm/cpufeature.h>
21 #include <asm/cputype.h>
22 #include <asm/daifflags.h>
23 #include <asm/debug-monitors.h>
24 #include <asm/system_misc.h>
25 #include <asm/traps.h>
26
27 /* Determine debug architecture. */
28 u8 debug_monitors_arch(void)
29 {
30 return cpuid_feature_extract_unsigned_field(read_sanitised_ftr_reg(SYS_ID_AA64DFR0_EL1),
31 ID_AA64DFR0_EL1_DebugVer_SHIFT);
32 }
33
34 /*
35 * MDSCR access routines.
36 */
37 static void mdscr_write(u32 mdscr)
38 {
39 unsigned long flags;
40 flags = local_daif_save();
41 write_sysreg(mdscr, mdscr_el1);
42 local_daif_restore(flags);
43 }
44 NOKPROBE_SYMBOL(mdscr_write);
45
46 static u32 mdscr_read(void)
47 {
48 return read_sysreg(mdscr_el1);
49 }
50 NOKPROBE_SYMBOL(mdscr_read);
51
52 /*
53 * Allow root to disable self-hosted debug from userspace.
54 * This is useful if you want to connect an external JTAG debugger.
55 */
56 static bool debug_enabled = true;
57
58 static int create_debug_debugfs_entry(void)
59 {
60 debugfs_create_bool("debug_enabled", 0644, NULL, &debug_enabled);
61 return 0;
62 }
63 fs_initcall(create_debug_debugfs_entry);
64
65 static int __init early_debug_disable(char *buf)
66 {
67 debug_enabled = false;
68 return 0;
69 }
70
71 early_param("nodebugmon", early_debug_disable);
72
73 /*
74 * Keep track of debug users on each core.
75 * The ref counts are per-cpu so we use a local_t type.
76 */
77 static DEFINE_PER_CPU(int, mde_ref_count);
78 static DEFINE_PER_CPU(int, kde_ref_count);
79
80 void enable_debug_monitors(enum dbg_active_el el)
81 {
82 u32 mdscr, enable = 0;
83
84 WARN_ON(preemptible());
85
86 if (this_cpu_inc_return(mde_ref_count) == 1)
87 enable = DBG_MDSCR_MDE;
88
89 if (el == DBG_ACTIVE_EL1 &&
90 this_cpu_inc_return(kde_ref_count) == 1)
91 enable |= DBG_MDSCR_KDE;
92
93 if (enable && debug_enabled) {
94 mdscr = mdscr_read();
95 mdscr |= enable;
96 mdscr_write(mdscr);
97 }
98 }
99 NOKPROBE_SYMBOL(enable_debug_monitors);
100
101 void disable_debug_monitors(enum dbg_active_el el)
102 {
103 u32 mdscr, disable = 0;
104
105 WARN_ON(preemptible());
106
107 if (this_cpu_dec_return(mde_ref_count) == 0)
108 disable = ~DBG_MDSCR_MDE;
109
110 if (el == DBG_ACTIVE_EL1 &&
111 this_cpu_dec_return(kde_ref_count) == 0)
112 disable &= ~DBG_MDSCR_KDE;
113
114 if (disable) {
115 mdscr = mdscr_read();
116 mdscr &= disable;
117 mdscr_write(mdscr);
118 }
119 }
120 NOKPROBE_SYMBOL(disable_debug_monitors);
121
122 /*
123 * OS lock clearing.
124 */
125 static int clear_os_lock(unsigned int cpu)
126 {
127 write_sysreg(0, osdlr_el1);
128 write_sysreg(0, oslar_el1);
129 isb();
130 return 0;
131 }
132
133 static int __init debug_monitors_init(void)
134 {
135 return cpuhp_setup_state(CPUHP_AP_ARM64_DEBUG_MONITORS_STARTING,
136 "arm64/debug_monitors:starting",
137 clear_os_lock, NULL);
138 }
139 postcore_initcall(debug_monitors_init);
140
141 /*
142 * Single step API and exception handling.
143 */
144 static void set_user_regs_spsr_ss(struct user_pt_regs *regs)
145 {
146 regs->pstate |= DBG_SPSR_SS;
147 }
148 NOKPROBE_SYMBOL(set_user_regs_spsr_ss);
149
150 static void clear_user_regs_spsr_ss(struct user_pt_regs *regs)
151 {
152 regs->pstate &= ~DBG_SPSR_SS;
153 }
154 NOKPROBE_SYMBOL(clear_user_regs_spsr_ss);
155
156 #define set_regs_spsr_ss(r) set_user_regs_spsr_ss(&(r)->user_regs)
157 #define clear_regs_spsr_ss(r) clear_user_regs_spsr_ss(&(r)->user_regs)
158
159 static DEFINE_SPINLOCK(debug_hook_lock);
160 static LIST_HEAD(user_step_hook);
161 static LIST_HEAD(kernel_step_hook);
162
163 static void register_debug_hook(struct list_head *node, struct list_head *list)
164 {
165 spin_lock(&debug_hook_lock);
166 list_add_rcu(node, list);
167 spin_unlock(&debug_hook_lock);
168
169 }
170
171 static void unregister_debug_hook(struct list_head *node)
172 {
173 spin_lock(&debug_hook_lock);
174 list_del_rcu(node);
175 spin_unlock(&debug_hook_lock);
176 synchronize_rcu();
177 }
178
179 void register_user_step_hook(struct step_hook *hook)
180 {
181 register_debug_hook(&hook->node, &user_step_hook);
182 }
183
184 void unregister_user_step_hook(struct step_hook *hook)
185 {
186 unregister_debug_hook(&hook->node);
187 }
188
189 void register_kernel_step_hook(struct step_hook *hook)
190 {
191 register_debug_hook(&hook->node, &kernel_step_hook);
192 }
193
194 void unregister_kernel_step_hook(struct step_hook *hook)
195 {
196 unregister_debug_hook(&hook->node);
197 }
198
199 /*
200 * Call registered single step handlers
201 * There is no Syndrome info to check for determining the handler.
202 * So we call all the registered handlers, until the right handler is
203 * found which returns zero.
204 */
205 static int call_step_hook(struct pt_regs *regs, unsigned long esr)
206 {
207 struct step_hook *hook;
208 struct list_head *list;
209 int retval = DBG_HOOK_ERROR;
210
211 list = user_mode(regs) ? &user_step_hook : &kernel_step_hook;
212
213 /*
214 * Since single-step exception disables interrupt, this function is
215 * entirely not preemptible, and we can use rcu list safely here.
216 */
217 list_for_each_entry_rcu(hook, list, node) {
218 retval = hook->fn(regs, esr);
219 if (retval == DBG_HOOK_HANDLED)
220 break;
221 }
222
223 return retval;
224 }
225 NOKPROBE_SYMBOL(call_step_hook);
226
227 static void send_user_sigtrap(int si_code)
228 {
229 struct pt_regs *regs = current_pt_regs();
230
231 if (WARN_ON(!user_mode(regs)))
232 return;
233
234 if (interrupts_enabled(regs))
235 local_irq_enable();
236
237 arm64_force_sig_fault(SIGTRAP, si_code, instruction_pointer(regs),
238 "User debug trap");
239 }
240
241 static int single_step_handler(unsigned long unused, unsigned long esr,
242 struct pt_regs *regs)
243 {
244 bool handler_found = false;
245
246 /*
247 * If we are stepping a pending breakpoint, call the hw_breakpoint
248 * handler first.
249 */
250 if (!reinstall_suspended_bps(regs))
251 return 0;
252
253 if (!handler_found && call_step_hook(regs, esr) == DBG_HOOK_HANDLED)
254 handler_found = true;
255
256 if (!handler_found && user_mode(regs)) {
257 send_user_sigtrap(TRAP_TRACE);
258
259 /*
260 * ptrace will disable single step unless explicitly
261 * asked to re-enable it. For other clients, it makes
262 * sense to leave it enabled (i.e. rewind the controls
263 * to the active-not-pending state).
264 */
265 user_rewind_single_step(current);
266 } else if (!handler_found) {
267 pr_warn("Unexpected kernel single-step exception at EL1\n");
268 /*
269 * Re-enable stepping since we know that we will be
270 * returning to regs.
271 */
272 set_regs_spsr_ss(regs);
273 }
274
275 return 0;
276 }
277 NOKPROBE_SYMBOL(single_step_handler);
278
279 static LIST_HEAD(user_break_hook);
280 static LIST_HEAD(kernel_break_hook);
281
282 void register_user_break_hook(struct break_hook *hook)
283 {
284 register_debug_hook(&hook->node, &user_break_hook);
285 }
286
287 void unregister_user_break_hook(struct break_hook *hook)
288 {
289 unregister_debug_hook(&hook->node);
290 }
291
292 void register_kernel_break_hook(struct break_hook *hook)
293 {
294 register_debug_hook(&hook->node, &kernel_break_hook);
295 }
296
297 void unregister_kernel_break_hook(struct break_hook *hook)
298 {
299 unregister_debug_hook(&hook->node);
300 }
301
302 static int call_break_hook(struct pt_regs *regs, unsigned long esr)
303 {
304 struct break_hook *hook;
305 struct list_head *list;
306 int (*fn)(struct pt_regs *regs, unsigned long esr) = NULL;
307
308 list = user_mode(regs) ? &user_break_hook : &kernel_break_hook;
309
310 /*
311 * Since brk exception disables interrupt, this function is
312 * entirely not preemptible, and we can use rcu list safely here.
313 */
314 list_for_each_entry_rcu(hook, list, node) {
315 if ((esr_brk_comment(esr) & ~hook->mask) == hook->imm)
316 fn = hook->fn;
317 }
318
319 return fn ? fn(regs, esr) : DBG_HOOK_ERROR;
320 }
321 NOKPROBE_SYMBOL(call_break_hook);
322
323 static int brk_handler(unsigned long unused, unsigned long esr,
324 struct pt_regs *regs)
325 {
326 if (call_break_hook(regs, esr) == DBG_HOOK_HANDLED)
327 return 0;
328
329 if (user_mode(regs)) {
330 send_user_sigtrap(TRAP_BRKPT);
331 } else {
332 pr_warn("Unexpected kernel BRK exception at EL1\n");
333 return -EFAULT;
334 }
335
336 return 0;
337 }
338 NOKPROBE_SYMBOL(brk_handler);
339
340 int aarch32_break_handler(struct pt_regs *regs)
341 {
342 u32 arm_instr;
343 u16 thumb_instr;
344 bool bp = false;
345 void __user *pc = (void __user *)instruction_pointer(regs);
346
347 if (!compat_user_mode(regs))
348 return -EFAULT;
349
350 if (compat_thumb_mode(regs)) {
351 /* get 16-bit Thumb instruction */
352 __le16 instr;
353 get_user(instr, (__le16 __user *)pc);
354 thumb_instr = le16_to_cpu(instr);
355 if (thumb_instr == AARCH32_BREAK_THUMB2_LO) {
356 /* get second half of 32-bit Thumb-2 instruction */
357 get_user(instr, (__le16 __user *)(pc + 2));
358 thumb_instr = le16_to_cpu(instr);
359 bp = thumb_instr == AARCH32_BREAK_THUMB2_HI;
360 } else {
361 bp = thumb_instr == AARCH32_BREAK_THUMB;
362 }
363 } else {
364 /* 32-bit ARM instruction */
365 __le32 instr;
366 get_user(instr, (__le32 __user *)pc);
367 arm_instr = le32_to_cpu(instr);
368 bp = (arm_instr & ~0xf0000000) == AARCH32_BREAK_ARM;
369 }
370
371 if (!bp)
372 return -EFAULT;
373
374 send_user_sigtrap(TRAP_BRKPT);
375 return 0;
376 }
377 NOKPROBE_SYMBOL(aarch32_break_handler);
378
379 void __init debug_traps_init(void)
380 {
381 hook_debug_fault_code(DBG_ESR_EVT_HWSS, single_step_handler, SIGTRAP,
382 TRAP_TRACE, "single-step handler");
383 hook_debug_fault_code(DBG_ESR_EVT_BRK, brk_handler, SIGTRAP,
384 TRAP_BRKPT, "BRK handler");
385 }
386
387 /* Re-enable single step for syscall restarting. */
388 void user_rewind_single_step(struct task_struct *task)
389 {
390 /*
391 * If single step is active for this thread, then set SPSR.SS
392 * to 1 to avoid returning to the active-pending state.
393 */
394 if (test_tsk_thread_flag(task, TIF_SINGLESTEP))
395 set_regs_spsr_ss(task_pt_regs(task));
396 }
397 NOKPROBE_SYMBOL(user_rewind_single_step);
398
399 void user_fastforward_single_step(struct task_struct *task)
400 {
401 if (test_tsk_thread_flag(task, TIF_SINGLESTEP))
402 clear_regs_spsr_ss(task_pt_regs(task));
403 }
404
405 void user_regs_reset_single_step(struct user_pt_regs *regs,
406 struct task_struct *task)
407 {
408 if (test_tsk_thread_flag(task, TIF_SINGLESTEP))
409 set_user_regs_spsr_ss(regs);
410 else
411 clear_user_regs_spsr_ss(regs);
412 }
413
414 /* Kernel API */
415 void kernel_enable_single_step(struct pt_regs *regs)
416 {
417 WARN_ON(!irqs_disabled());
418 set_regs_spsr_ss(regs);
419 mdscr_write(mdscr_read() | DBG_MDSCR_SS);
420 enable_debug_monitors(DBG_ACTIVE_EL1);
421 }
422 NOKPROBE_SYMBOL(kernel_enable_single_step);
423
424 void kernel_disable_single_step(void)
425 {
426 WARN_ON(!irqs_disabled());
427 mdscr_write(mdscr_read() & ~DBG_MDSCR_SS);
428 disable_debug_monitors(DBG_ACTIVE_EL1);
429 }
430 NOKPROBE_SYMBOL(kernel_disable_single_step);
431
432 int kernel_active_single_step(void)
433 {
434 WARN_ON(!irqs_disabled());
435 return mdscr_read() & DBG_MDSCR_SS;
436 }
437 NOKPROBE_SYMBOL(kernel_active_single_step);
438
439 void kernel_rewind_single_step(struct pt_regs *regs)
440 {
441 set_regs_spsr_ss(regs);
442 }
443
444 /* ptrace API */
445 void user_enable_single_step(struct task_struct *task)
446 {
447 struct thread_info *ti = task_thread_info(task);
448
449 if (!test_and_set_ti_thread_flag(ti, TIF_SINGLESTEP))
450 set_regs_spsr_ss(task_pt_regs(task));
451 }
452 NOKPROBE_SYMBOL(user_enable_single_step);
453
454 void user_disable_single_step(struct task_struct *task)
455 {
456 clear_ti_thread_flag(task_thread_info(task), TIF_SINGLESTEP);
457 }
458 NOKPROBE_SYMBOL(user_disable_single_step);
459
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