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