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. */
28u8 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 */
37static 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}
44NOKPROBE_SYMBOL(mdscr_write);
45
46static u32 mdscr_read(void)
47{
48	return read_sysreg(mdscr_el1);
49}
50NOKPROBE_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 */
56static bool debug_enabled = true;
57
58static int create_debug_debugfs_entry(void)
59{
60	debugfs_create_bool("debug_enabled", 0644, NULL, &debug_enabled);
61	return 0;
62}
63fs_initcall(create_debug_debugfs_entry);
64
65static int __init early_debug_disable(char *buf)
66{
67	debug_enabled = false;
68	return 0;
69}
70
71early_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 */
77static DEFINE_PER_CPU(int, mde_ref_count);
78static DEFINE_PER_CPU(int, kde_ref_count);
79
80void 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}
99NOKPROBE_SYMBOL(enable_debug_monitors);
100
101void 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}
120NOKPROBE_SYMBOL(disable_debug_monitors);
121
122/*
123 * OS lock clearing.
124 */
125static 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
133static 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}
139postcore_initcall(debug_monitors_init);
140
141/*
142 * Single step API and exception handling.
143 */
144static void set_user_regs_spsr_ss(struct user_pt_regs *regs)
145{
146	regs->pstate |= DBG_SPSR_SS;
147}
148NOKPROBE_SYMBOL(set_user_regs_spsr_ss);
149
150static void clear_user_regs_spsr_ss(struct user_pt_regs *regs)
151{
152	regs->pstate &= ~DBG_SPSR_SS;
153}
154NOKPROBE_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
159static DEFINE_SPINLOCK(debug_hook_lock);
160static LIST_HEAD(user_step_hook);
161static LIST_HEAD(kernel_step_hook);
162
163static 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
171static 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
179void register_user_step_hook(struct step_hook *hook)
180{
181	register_debug_hook(&hook->node, &user_step_hook);
182}
183
184void unregister_user_step_hook(struct step_hook *hook)
185{
186	unregister_debug_hook(&hook->node);
187}
188
189void register_kernel_step_hook(struct step_hook *hook)
190{
191	register_debug_hook(&hook->node, &kernel_step_hook);
192}
193
194void 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 */
205static 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}
225NOKPROBE_SYMBOL(call_step_hook);
226
227static 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
241static 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}
277NOKPROBE_SYMBOL(single_step_handler);
278
279static LIST_HEAD(user_break_hook);
280static LIST_HEAD(kernel_break_hook);
281
282void register_user_break_hook(struct break_hook *hook)
283{
284	register_debug_hook(&hook->node, &user_break_hook);
285}
286
287void unregister_user_break_hook(struct break_hook *hook)
288{
289	unregister_debug_hook(&hook->node);
290}
291
292void register_kernel_break_hook(struct break_hook *hook)
293{
294	register_debug_hook(&hook->node, &kernel_break_hook);
295}
296
297void unregister_kernel_break_hook(struct break_hook *hook)
298{
299	unregister_debug_hook(&hook->node);
300}
301
302static 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		unsigned long comment = esr & ESR_ELx_BRK64_ISS_COMMENT_MASK;
316
317		if ((comment & ~hook->mask) == hook->imm)
318			fn = hook->fn;
319	}
320
321	return fn ? fn(regs, esr) : DBG_HOOK_ERROR;
322}
323NOKPROBE_SYMBOL(call_break_hook);
324
325static int brk_handler(unsigned long unused, unsigned long esr,
326		       struct pt_regs *regs)
327{
328	if (call_break_hook(regs, esr) == DBG_HOOK_HANDLED)
329		return 0;
330
331	if (user_mode(regs)) {
332		send_user_sigtrap(TRAP_BRKPT);
333	} else {
334		pr_warn("Unexpected kernel BRK exception at EL1\n");
335		return -EFAULT;
336	}
337
338	return 0;
339}
340NOKPROBE_SYMBOL(brk_handler);
341
342int aarch32_break_handler(struct pt_regs *regs)
343{
344	u32 arm_instr;
345	u16 thumb_instr;
346	bool bp = false;
347	void __user *pc = (void __user *)instruction_pointer(regs);
348
349	if (!compat_user_mode(regs))
350		return -EFAULT;
351
352	if (compat_thumb_mode(regs)) {
353		/* get 16-bit Thumb instruction */
354		__le16 instr;
355		get_user(instr, (__le16 __user *)pc);
356		thumb_instr = le16_to_cpu(instr);
357		if (thumb_instr == AARCH32_BREAK_THUMB2_LO) {
358			/* get second half of 32-bit Thumb-2 instruction */
359			get_user(instr, (__le16 __user *)(pc + 2));
360			thumb_instr = le16_to_cpu(instr);
361			bp = thumb_instr == AARCH32_BREAK_THUMB2_HI;
362		} else {
363			bp = thumb_instr == AARCH32_BREAK_THUMB;
364		}
365	} else {
366		/* 32-bit ARM instruction */
367		__le32 instr;
368		get_user(instr, (__le32 __user *)pc);
369		arm_instr = le32_to_cpu(instr);
370		bp = (arm_instr & ~0xf0000000) == AARCH32_BREAK_ARM;
371	}
372
373	if (!bp)
374		return -EFAULT;
375
376	send_user_sigtrap(TRAP_BRKPT);
377	return 0;
378}
379NOKPROBE_SYMBOL(aarch32_break_handler);
380
381void __init debug_traps_init(void)
382{
383	hook_debug_fault_code(DBG_ESR_EVT_HWSS, single_step_handler, SIGTRAP,
384			      TRAP_TRACE, "single-step handler");
385	hook_debug_fault_code(DBG_ESR_EVT_BRK, brk_handler, SIGTRAP,
386			      TRAP_BRKPT, "BRK handler");
387}
388
389/* Re-enable single step for syscall restarting. */
390void user_rewind_single_step(struct task_struct *task)
391{
392	/*
393	 * If single step is active for this thread, then set SPSR.SS
394	 * to 1 to avoid returning to the active-pending state.
395	 */
396	if (test_tsk_thread_flag(task, TIF_SINGLESTEP))
397		set_regs_spsr_ss(task_pt_regs(task));
398}
399NOKPROBE_SYMBOL(user_rewind_single_step);
400
401void user_fastforward_single_step(struct task_struct *task)
402{
403	if (test_tsk_thread_flag(task, TIF_SINGLESTEP))
404		clear_regs_spsr_ss(task_pt_regs(task));
405}
406
407void user_regs_reset_single_step(struct user_pt_regs *regs,
408				 struct task_struct *task)
409{
410	if (test_tsk_thread_flag(task, TIF_SINGLESTEP))
411		set_user_regs_spsr_ss(regs);
412	else
413		clear_user_regs_spsr_ss(regs);
414}
415
416/* Kernel API */
417void kernel_enable_single_step(struct pt_regs *regs)
418{
419	WARN_ON(!irqs_disabled());
420	set_regs_spsr_ss(regs);
421	mdscr_write(mdscr_read() | DBG_MDSCR_SS);
422	enable_debug_monitors(DBG_ACTIVE_EL1);
423}
424NOKPROBE_SYMBOL(kernel_enable_single_step);
425
426void kernel_disable_single_step(void)
427{
428	WARN_ON(!irqs_disabled());
429	mdscr_write(mdscr_read() & ~DBG_MDSCR_SS);
430	disable_debug_monitors(DBG_ACTIVE_EL1);
431}
432NOKPROBE_SYMBOL(kernel_disable_single_step);
433
434int kernel_active_single_step(void)
435{
436	WARN_ON(!irqs_disabled());
437	return mdscr_read() & DBG_MDSCR_SS;
438}
439NOKPROBE_SYMBOL(kernel_active_single_step);
440
441void kernel_rewind_single_step(struct pt_regs *regs)
442{
443	set_regs_spsr_ss(regs);
444}
445
446/* ptrace API */
447void user_enable_single_step(struct task_struct *task)
448{
449	struct thread_info *ti = task_thread_info(task);
450
451	if (!test_and_set_ti_thread_flag(ti, TIF_SINGLESTEP))
452		set_regs_spsr_ss(task_pt_regs(task));
453}
454NOKPROBE_SYMBOL(user_enable_single_step);
455
456void user_disable_single_step(struct task_struct *task)
457{
458	clear_ti_thread_flag(task_thread_info(task), TIF_SINGLESTEP);
459}
460NOKPROBE_SYMBOL(user_disable_single_step);
461