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/exception.h>
25 #include <asm/kgdb.h>
26 #include <asm/kprobes.h>
27 #include <asm/system_misc.h>
28 #include <asm/traps.h>
29 #include <asm/uprobes.h>
30
31 /* Determine debug architecture. */
debug_monitors_arch(void)32 u8 debug_monitors_arch(void)
33 {
34 return cpuid_feature_extract_unsigned_field(read_sanitised_ftr_reg(SYS_ID_AA64DFR0_EL1),
35 ID_AA64DFR0_EL1_DebugVer_SHIFT);
36 }
37
38 /*
39 * MDSCR access routines.
40 */
mdscr_write(u64 mdscr)41 static void mdscr_write(u64 mdscr)
42 {
43 unsigned long flags;
44 flags = local_daif_save();
45 write_sysreg(mdscr, mdscr_el1);
46 local_daif_restore(flags);
47 }
48 NOKPROBE_SYMBOL(mdscr_write);
49
mdscr_read(void)50 static u64 mdscr_read(void)
51 {
52 return read_sysreg(mdscr_el1);
53 }
54 NOKPROBE_SYMBOL(mdscr_read);
55
56 /*
57 * Allow root to disable self-hosted debug from userspace.
58 * This is useful if you want to connect an external JTAG debugger.
59 */
60 static bool debug_enabled = true;
61
create_debug_debugfs_entry(void)62 static int create_debug_debugfs_entry(void)
63 {
64 debugfs_create_bool("debug_enabled", 0644, NULL, &debug_enabled);
65 return 0;
66 }
67 fs_initcall(create_debug_debugfs_entry);
68
early_debug_disable(char * buf)69 static int __init early_debug_disable(char *buf)
70 {
71 debug_enabled = false;
72 return 0;
73 }
74
75 early_param("nodebugmon", early_debug_disable);
76
77 /*
78 * Keep track of debug users on each core.
79 * The ref counts are per-cpu so we use a local_t type.
80 */
81 static DEFINE_PER_CPU(int, mde_ref_count);
82 static DEFINE_PER_CPU(int, kde_ref_count);
83
enable_debug_monitors(enum dbg_active_el el)84 void enable_debug_monitors(enum dbg_active_el el)
85 {
86 u64 mdscr, enable = 0;
87
88 WARN_ON(preemptible());
89
90 if (this_cpu_inc_return(mde_ref_count) == 1)
91 enable = MDSCR_EL1_MDE;
92
93 if (el == DBG_ACTIVE_EL1 &&
94 this_cpu_inc_return(kde_ref_count) == 1)
95 enable |= MDSCR_EL1_KDE;
96
97 if (enable && debug_enabled) {
98 mdscr = mdscr_read();
99 mdscr |= enable;
100 mdscr_write(mdscr);
101 }
102 }
103 NOKPROBE_SYMBOL(enable_debug_monitors);
104
disable_debug_monitors(enum dbg_active_el el)105 void disable_debug_monitors(enum dbg_active_el el)
106 {
107 u64 mdscr, disable = 0;
108
109 WARN_ON(preemptible());
110
111 if (this_cpu_dec_return(mde_ref_count) == 0)
112 disable = ~MDSCR_EL1_MDE;
113
114 if (el == DBG_ACTIVE_EL1 &&
115 this_cpu_dec_return(kde_ref_count) == 0)
116 disable &= ~MDSCR_EL1_KDE;
117
118 if (disable) {
119 mdscr = mdscr_read();
120 mdscr &= disable;
121 mdscr_write(mdscr);
122 }
123 }
124 NOKPROBE_SYMBOL(disable_debug_monitors);
125
126 /*
127 * OS lock clearing.
128 */
clear_os_lock(unsigned int cpu)129 static int clear_os_lock(unsigned int cpu)
130 {
131 write_sysreg(0, osdlr_el1);
132 write_sysreg(0, oslar_el1);
133 isb();
134 return 0;
135 }
136
debug_monitors_init(void)137 static int __init debug_monitors_init(void)
138 {
139 return cpuhp_setup_state(CPUHP_AP_ARM64_DEBUG_MONITORS_STARTING,
140 "arm64/debug_monitors:starting",
141 clear_os_lock, NULL);
142 }
143 postcore_initcall(debug_monitors_init);
144
145 /*
146 * Single step API and exception handling.
147 */
set_user_regs_spsr_ss(struct user_pt_regs * regs)148 static void set_user_regs_spsr_ss(struct user_pt_regs *regs)
149 {
150 regs->pstate |= DBG_SPSR_SS;
151 }
152 NOKPROBE_SYMBOL(set_user_regs_spsr_ss);
153
clear_user_regs_spsr_ss(struct user_pt_regs * regs)154 static void clear_user_regs_spsr_ss(struct user_pt_regs *regs)
155 {
156 regs->pstate &= ~DBG_SPSR_SS;
157 }
158 NOKPROBE_SYMBOL(clear_user_regs_spsr_ss);
159
160 #define set_regs_spsr_ss(r) set_user_regs_spsr_ss(&(r)->user_regs)
161 #define clear_regs_spsr_ss(r) clear_user_regs_spsr_ss(&(r)->user_regs)
162
send_user_sigtrap(int si_code)163 static void send_user_sigtrap(int si_code)
164 {
165 struct pt_regs *regs = current_pt_regs();
166
167 if (WARN_ON(!user_mode(regs)))
168 return;
169
170 if (interrupts_enabled(regs))
171 local_irq_enable();
172
173 arm64_force_sig_fault(SIGTRAP, si_code, instruction_pointer(regs),
174 "User debug trap");
175 }
176
177 /*
178 * We have already unmasked interrupts and enabled preemption
179 * when calling do_el0_softstep() from entry-common.c.
180 */
do_el0_softstep(unsigned long esr,struct pt_regs * regs)181 void do_el0_softstep(unsigned long esr, struct pt_regs *regs)
182 {
183 if (uprobe_single_step_handler(regs, esr) == DBG_HOOK_HANDLED)
184 return;
185
186 send_user_sigtrap(TRAP_TRACE);
187 /*
188 * ptrace will disable single step unless explicitly
189 * asked to re-enable it. For other clients, it makes
190 * sense to leave it enabled (i.e. rewind the controls
191 * to the active-not-pending state).
192 */
193 user_rewind_single_step(current);
194 }
195
do_el1_softstep(unsigned long esr,struct pt_regs * regs)196 void do_el1_softstep(unsigned long esr, struct pt_regs *regs)
197 {
198 if (kgdb_single_step_handler(regs, esr) == DBG_HOOK_HANDLED)
199 return;
200
201 pr_warn("Unexpected kernel single-step exception at EL1\n");
202 /*
203 * Re-enable stepping since we know that we will be
204 * returning to regs.
205 */
206 set_regs_spsr_ss(regs);
207 }
208 NOKPROBE_SYMBOL(do_el1_softstep);
209
call_el1_break_hook(struct pt_regs * regs,unsigned long esr)210 static int call_el1_break_hook(struct pt_regs *regs, unsigned long esr)
211 {
212 if (esr_brk_comment(esr) == BUG_BRK_IMM)
213 return bug_brk_handler(regs, esr);
214
215 if (IS_ENABLED(CONFIG_CFI_CLANG) && esr_is_cfi_brk(esr))
216 return cfi_brk_handler(regs, esr);
217
218 if (esr_brk_comment(esr) == FAULT_BRK_IMM)
219 return reserved_fault_brk_handler(regs, esr);
220
221 if (IS_ENABLED(CONFIG_KASAN_SW_TAGS) &&
222 (esr_brk_comment(esr) & ~KASAN_BRK_MASK) == KASAN_BRK_IMM)
223 return kasan_brk_handler(regs, esr);
224
225 if (IS_ENABLED(CONFIG_UBSAN_TRAP) && esr_is_ubsan_brk(esr))
226 return ubsan_brk_handler(regs, esr);
227
228 if (IS_ENABLED(CONFIG_KGDB)) {
229 if (esr_brk_comment(esr) == KGDB_DYN_DBG_BRK_IMM)
230 return kgdb_brk_handler(regs, esr);
231 if (esr_brk_comment(esr) == KGDB_COMPILED_DBG_BRK_IMM)
232 return kgdb_compiled_brk_handler(regs, esr);
233 }
234
235 if (IS_ENABLED(CONFIG_KPROBES)) {
236 if (esr_brk_comment(esr) == KPROBES_BRK_IMM)
237 return kprobe_brk_handler(regs, esr);
238 if (esr_brk_comment(esr) == KPROBES_BRK_SS_IMM)
239 return kprobe_ss_brk_handler(regs, esr);
240 }
241
242 if (IS_ENABLED(CONFIG_KRETPROBES) &&
243 esr_brk_comment(esr) == KRETPROBES_BRK_IMM)
244 return kretprobe_brk_handler(regs, esr);
245
246 return DBG_HOOK_ERROR;
247 }
248 NOKPROBE_SYMBOL(call_el1_break_hook);
249
250 /*
251 * We have already unmasked interrupts and enabled preemption
252 * when calling do_el0_brk64() from entry-common.c.
253 */
do_el0_brk64(unsigned long esr,struct pt_regs * regs)254 void do_el0_brk64(unsigned long esr, struct pt_regs *regs)
255 {
256 if (IS_ENABLED(CONFIG_UPROBES) &&
257 esr_brk_comment(esr) == UPROBES_BRK_IMM &&
258 uprobe_brk_handler(regs, esr) == DBG_HOOK_HANDLED)
259 return;
260
261 send_user_sigtrap(TRAP_BRKPT);
262 }
263
do_el1_brk64(unsigned long esr,struct pt_regs * regs)264 void do_el1_brk64(unsigned long esr, struct pt_regs *regs)
265 {
266 if (call_el1_break_hook(regs, esr) == DBG_HOOK_HANDLED)
267 return;
268
269 die("Oops - BRK", regs, esr);
270 }
271 NOKPROBE_SYMBOL(do_el1_brk64);
272
273 #ifdef CONFIG_COMPAT
do_bkpt32(unsigned long esr,struct pt_regs * regs)274 void do_bkpt32(unsigned long esr, struct pt_regs *regs)
275 {
276 arm64_notify_die("aarch32 BKPT", regs, SIGTRAP, TRAP_BRKPT, regs->pc, esr);
277 }
278 #endif /* CONFIG_COMPAT */
279
try_handle_aarch32_break(struct pt_regs * regs)280 bool try_handle_aarch32_break(struct pt_regs *regs)
281 {
282 u32 arm_instr;
283 u16 thumb_instr;
284 bool bp = false;
285 void __user *pc = (void __user *)instruction_pointer(regs);
286
287 if (!compat_user_mode(regs))
288 return false;
289
290 if (compat_thumb_mode(regs)) {
291 /* get 16-bit Thumb instruction */
292 __le16 instr;
293 get_user(instr, (__le16 __user *)pc);
294 thumb_instr = le16_to_cpu(instr);
295 if (thumb_instr == AARCH32_BREAK_THUMB2_LO) {
296 /* get second half of 32-bit Thumb-2 instruction */
297 get_user(instr, (__le16 __user *)(pc + 2));
298 thumb_instr = le16_to_cpu(instr);
299 bp = thumb_instr == AARCH32_BREAK_THUMB2_HI;
300 } else {
301 bp = thumb_instr == AARCH32_BREAK_THUMB;
302 }
303 } else {
304 /* 32-bit ARM instruction */
305 __le32 instr;
306 get_user(instr, (__le32 __user *)pc);
307 arm_instr = le32_to_cpu(instr);
308 bp = (arm_instr & ~0xf0000000) == AARCH32_BREAK_ARM;
309 }
310
311 if (!bp)
312 return false;
313
314 send_user_sigtrap(TRAP_BRKPT);
315 return true;
316 }
317 NOKPROBE_SYMBOL(try_handle_aarch32_break);
318
319 /* Re-enable single step for syscall restarting. */
user_rewind_single_step(struct task_struct * task)320 void user_rewind_single_step(struct task_struct *task)
321 {
322 /*
323 * If single step is active for this thread, then set SPSR.SS
324 * to 1 to avoid returning to the active-pending state.
325 */
326 if (test_tsk_thread_flag(task, TIF_SINGLESTEP))
327 set_regs_spsr_ss(task_pt_regs(task));
328 }
329 NOKPROBE_SYMBOL(user_rewind_single_step);
330
user_fastforward_single_step(struct task_struct * task)331 void user_fastforward_single_step(struct task_struct *task)
332 {
333 if (test_tsk_thread_flag(task, TIF_SINGLESTEP))
334 clear_regs_spsr_ss(task_pt_regs(task));
335 }
336
user_regs_reset_single_step(struct user_pt_regs * regs,struct task_struct * task)337 void user_regs_reset_single_step(struct user_pt_regs *regs,
338 struct task_struct *task)
339 {
340 if (test_tsk_thread_flag(task, TIF_SINGLESTEP))
341 set_user_regs_spsr_ss(regs);
342 else
343 clear_user_regs_spsr_ss(regs);
344 }
345
346 /* Kernel API */
kernel_enable_single_step(struct pt_regs * regs)347 void kernel_enable_single_step(struct pt_regs *regs)
348 {
349 WARN_ON(!irqs_disabled());
350 set_regs_spsr_ss(regs);
351 mdscr_write(mdscr_read() | MDSCR_EL1_SS);
352 enable_debug_monitors(DBG_ACTIVE_EL1);
353 }
354 NOKPROBE_SYMBOL(kernel_enable_single_step);
355
kernel_disable_single_step(void)356 void kernel_disable_single_step(void)
357 {
358 WARN_ON(!irqs_disabled());
359 mdscr_write(mdscr_read() & ~MDSCR_EL1_SS);
360 disable_debug_monitors(DBG_ACTIVE_EL1);
361 }
362 NOKPROBE_SYMBOL(kernel_disable_single_step);
363
kernel_active_single_step(void)364 int kernel_active_single_step(void)
365 {
366 WARN_ON(!irqs_disabled());
367 return mdscr_read() & MDSCR_EL1_SS;
368 }
369 NOKPROBE_SYMBOL(kernel_active_single_step);
370
kernel_rewind_single_step(struct pt_regs * regs)371 void kernel_rewind_single_step(struct pt_regs *regs)
372 {
373 set_regs_spsr_ss(regs);
374 }
375
kernel_fastforward_single_step(struct pt_regs * regs)376 void kernel_fastforward_single_step(struct pt_regs *regs)
377 {
378 clear_regs_spsr_ss(regs);
379 }
380
381 /* ptrace API */
user_enable_single_step(struct task_struct * task)382 void user_enable_single_step(struct task_struct *task)
383 {
384 struct thread_info *ti = task_thread_info(task);
385
386 if (!test_and_set_ti_thread_flag(ti, TIF_SINGLESTEP))
387 set_regs_spsr_ss(task_pt_regs(task));
388 }
389 NOKPROBE_SYMBOL(user_enable_single_step);
390
user_disable_single_step(struct task_struct * task)391 void user_disable_single_step(struct task_struct *task)
392 {
393 clear_ti_thread_flag(task_thread_info(task), TIF_SINGLESTEP);
394 }
395 NOKPROBE_SYMBOL(user_disable_single_step);
396