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_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 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_regs_spsr_ss(struct pt_regs *regs)
145 {
146 	regs->pstate |= DBG_SPSR_SS;
147 }
148 NOKPROBE_SYMBOL(set_regs_spsr_ss);
149 
150 static void clear_regs_spsr_ss(struct pt_regs *regs)
151 {
152 	regs->pstate &= ~DBG_SPSR_SS;
153 }
154 NOKPROBE_SYMBOL(clear_regs_spsr_ss);
155 
156 static DEFINE_SPINLOCK(debug_hook_lock);
157 static LIST_HEAD(user_step_hook);
158 static LIST_HEAD(kernel_step_hook);
159 
160 static void register_debug_hook(struct list_head *node, struct list_head *list)
161 {
162 	spin_lock(&debug_hook_lock);
163 	list_add_rcu(node, list);
164 	spin_unlock(&debug_hook_lock);
165 
166 }
167 
168 static void unregister_debug_hook(struct list_head *node)
169 {
170 	spin_lock(&debug_hook_lock);
171 	list_del_rcu(node);
172 	spin_unlock(&debug_hook_lock);
173 	synchronize_rcu();
174 }
175 
176 void register_user_step_hook(struct step_hook *hook)
177 {
178 	register_debug_hook(&hook->node, &user_step_hook);
179 }
180 
181 void unregister_user_step_hook(struct step_hook *hook)
182 {
183 	unregister_debug_hook(&hook->node);
184 }
185 
186 void register_kernel_step_hook(struct step_hook *hook)
187 {
188 	register_debug_hook(&hook->node, &kernel_step_hook);
189 }
190 
191 void unregister_kernel_step_hook(struct step_hook *hook)
192 {
193 	unregister_debug_hook(&hook->node);
194 }
195 
196 /*
197  * Call registered single step handlers
198  * There is no Syndrome info to check for determining the handler.
199  * So we call all the registered handlers, until the right handler is
200  * found which returns zero.
201  */
202 static int call_step_hook(struct pt_regs *regs, unsigned int esr)
203 {
204 	struct step_hook *hook;
205 	struct list_head *list;
206 	int retval = DBG_HOOK_ERROR;
207 
208 	list = user_mode(regs) ? &user_step_hook : &kernel_step_hook;
209 
210 	rcu_read_lock();
211 
212 	list_for_each_entry_rcu(hook, list, node)	{
213 		retval = hook->fn(regs, esr);
214 		if (retval == DBG_HOOK_HANDLED)
215 			break;
216 	}
217 
218 	rcu_read_unlock();
219 
220 	return retval;
221 }
222 NOKPROBE_SYMBOL(call_step_hook);
223 
224 static void send_user_sigtrap(int si_code)
225 {
226 	struct pt_regs *regs = current_pt_regs();
227 
228 	if (WARN_ON(!user_mode(regs)))
229 		return;
230 
231 	if (interrupts_enabled(regs))
232 		local_irq_enable();
233 
234 	arm64_force_sig_fault(SIGTRAP, si_code,
235 			     (void __user *)instruction_pointer(regs),
236 			     "User debug trap");
237 }
238 
239 static int single_step_handler(unsigned long unused, unsigned int esr,
240 			       struct pt_regs *regs)
241 {
242 	bool handler_found = false;
243 
244 	/*
245 	 * If we are stepping a pending breakpoint, call the hw_breakpoint
246 	 * handler first.
247 	 */
248 	if (!reinstall_suspended_bps(regs))
249 		return 0;
250 
251 	if (!handler_found && call_step_hook(regs, esr) == DBG_HOOK_HANDLED)
252 		handler_found = true;
253 
254 	if (!handler_found && user_mode(regs)) {
255 		send_user_sigtrap(TRAP_TRACE);
256 
257 		/*
258 		 * ptrace will disable single step unless explicitly
259 		 * asked to re-enable it. For other clients, it makes
260 		 * sense to leave it enabled (i.e. rewind the controls
261 		 * to the active-not-pending state).
262 		 */
263 		user_rewind_single_step(current);
264 	} else if (!handler_found) {
265 		pr_warn("Unexpected kernel single-step exception at EL1\n");
266 		/*
267 		 * Re-enable stepping since we know that we will be
268 		 * returning to regs.
269 		 */
270 		set_regs_spsr_ss(regs);
271 	}
272 
273 	return 0;
274 }
275 NOKPROBE_SYMBOL(single_step_handler);
276 
277 static LIST_HEAD(user_break_hook);
278 static LIST_HEAD(kernel_break_hook);
279 
280 void register_user_break_hook(struct break_hook *hook)
281 {
282 	register_debug_hook(&hook->node, &user_break_hook);
283 }
284 
285 void unregister_user_break_hook(struct break_hook *hook)
286 {
287 	unregister_debug_hook(&hook->node);
288 }
289 
290 void register_kernel_break_hook(struct break_hook *hook)
291 {
292 	register_debug_hook(&hook->node, &kernel_break_hook);
293 }
294 
295 void unregister_kernel_break_hook(struct break_hook *hook)
296 {
297 	unregister_debug_hook(&hook->node);
298 }
299 
300 static int call_break_hook(struct pt_regs *regs, unsigned int esr)
301 {
302 	struct break_hook *hook;
303 	struct list_head *list;
304 	int (*fn)(struct pt_regs *regs, unsigned int esr) = NULL;
305 
306 	list = user_mode(regs) ? &user_break_hook : &kernel_break_hook;
307 
308 	rcu_read_lock();
309 	list_for_each_entry_rcu(hook, list, node) {
310 		unsigned int comment = esr & ESR_ELx_BRK64_ISS_COMMENT_MASK;
311 
312 		if ((comment & ~hook->mask) == hook->imm)
313 			fn = hook->fn;
314 	}
315 	rcu_read_unlock();
316 
317 	return fn ? fn(regs, esr) : DBG_HOOK_ERROR;
318 }
319 NOKPROBE_SYMBOL(call_break_hook);
320 
321 static int brk_handler(unsigned long unused, unsigned int esr,
322 		       struct pt_regs *regs)
323 {
324 	if (call_break_hook(regs, esr) == DBG_HOOK_HANDLED)
325 		return 0;
326 
327 	if (user_mode(regs)) {
328 		send_user_sigtrap(TRAP_BRKPT);
329 	} else {
330 		pr_warn("Unexpected kernel BRK exception at EL1\n");
331 		return -EFAULT;
332 	}
333 
334 	return 0;
335 }
336 NOKPROBE_SYMBOL(brk_handler);
337 
338 int aarch32_break_handler(struct pt_regs *regs)
339 {
340 	u32 arm_instr;
341 	u16 thumb_instr;
342 	bool bp = false;
343 	void __user *pc = (void __user *)instruction_pointer(regs);
344 
345 	if (!compat_user_mode(regs))
346 		return -EFAULT;
347 
348 	if (compat_thumb_mode(regs)) {
349 		/* get 16-bit Thumb instruction */
350 		__le16 instr;
351 		get_user(instr, (__le16 __user *)pc);
352 		thumb_instr = le16_to_cpu(instr);
353 		if (thumb_instr == AARCH32_BREAK_THUMB2_LO) {
354 			/* get second half of 32-bit Thumb-2 instruction */
355 			get_user(instr, (__le16 __user *)(pc + 2));
356 			thumb_instr = le16_to_cpu(instr);
357 			bp = thumb_instr == AARCH32_BREAK_THUMB2_HI;
358 		} else {
359 			bp = thumb_instr == AARCH32_BREAK_THUMB;
360 		}
361 	} else {
362 		/* 32-bit ARM instruction */
363 		__le32 instr;
364 		get_user(instr, (__le32 __user *)pc);
365 		arm_instr = le32_to_cpu(instr);
366 		bp = (arm_instr & ~0xf0000000) == AARCH32_BREAK_ARM;
367 	}
368 
369 	if (!bp)
370 		return -EFAULT;
371 
372 	send_user_sigtrap(TRAP_BRKPT);
373 	return 0;
374 }
375 NOKPROBE_SYMBOL(aarch32_break_handler);
376 
377 static int __init debug_traps_init(void)
378 {
379 	hook_debug_fault_code(DBG_ESR_EVT_HWSS, single_step_handler, SIGTRAP,
380 			      TRAP_TRACE, "single-step handler");
381 	hook_debug_fault_code(DBG_ESR_EVT_BRK, brk_handler, SIGTRAP,
382 			      TRAP_BRKPT, "ptrace BRK handler");
383 	return 0;
384 }
385 arch_initcall(debug_traps_init);
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_ti_thread_flag(task_thread_info(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_ti_thread_flag(task_thread_info(task), TIF_SINGLESTEP))
402 		clear_regs_spsr_ss(task_pt_regs(task));
403 }
404 
405 /* Kernel API */
406 void kernel_enable_single_step(struct pt_regs *regs)
407 {
408 	WARN_ON(!irqs_disabled());
409 	set_regs_spsr_ss(regs);
410 	mdscr_write(mdscr_read() | DBG_MDSCR_SS);
411 	enable_debug_monitors(DBG_ACTIVE_EL1);
412 }
413 NOKPROBE_SYMBOL(kernel_enable_single_step);
414 
415 void kernel_disable_single_step(void)
416 {
417 	WARN_ON(!irqs_disabled());
418 	mdscr_write(mdscr_read() & ~DBG_MDSCR_SS);
419 	disable_debug_monitors(DBG_ACTIVE_EL1);
420 }
421 NOKPROBE_SYMBOL(kernel_disable_single_step);
422 
423 int kernel_active_single_step(void)
424 {
425 	WARN_ON(!irqs_disabled());
426 	return mdscr_read() & DBG_MDSCR_SS;
427 }
428 NOKPROBE_SYMBOL(kernel_active_single_step);
429 
430 /* ptrace API */
431 void user_enable_single_step(struct task_struct *task)
432 {
433 	struct thread_info *ti = task_thread_info(task);
434 
435 	if (!test_and_set_ti_thread_flag(ti, TIF_SINGLESTEP))
436 		set_regs_spsr_ss(task_pt_regs(task));
437 }
438 NOKPROBE_SYMBOL(user_enable_single_step);
439 
440 void user_disable_single_step(struct task_struct *task)
441 {
442 	clear_ti_thread_flag(task_thread_info(task), TIF_SINGLESTEP);
443 }
444 NOKPROBE_SYMBOL(user_disable_single_step);
445