1 /*
2  * ARMv8 single-step debug support and mdscr context switching.
3  *
4  * Copyright (C) 2012 ARM Limited
5  *
6  * This program is free software; you can redistribute it and/or modify
7  * it under the terms of the GNU General Public License version 2 as
8  * published by the Free Software Foundation.
9  *
10  * This program is distributed in the hope that it will be useful,
11  * but WITHOUT ANY WARRANTY; without even the implied warranty of
12  * MERCHANTABILITY or FITNESS FOR A PARTICULAR PURPOSE.  See the
13  * GNU General Public License for more details.
14  *
15  * You should have received a copy of the GNU General Public License
16  * along with this program.  If not, see <http://www.gnu.org/licenses/>.
17  *
18  * Author: Will Deacon <will.deacon@arm.com>
19  */
20 
21 #include <linux/cpu.h>
22 #include <linux/debugfs.h>
23 #include <linux/hardirq.h>
24 #include <linux/init.h>
25 #include <linux/ptrace.h>
26 #include <linux/stat.h>
27 #include <linux/uaccess.h>
28 
29 #include <asm/cpufeature.h>
30 #include <asm/cputype.h>
31 #include <asm/debug-monitors.h>
32 #include <asm/system_misc.h>
33 
34 /* Determine debug architecture. */
35 u8 debug_monitors_arch(void)
36 {
37 	return cpuid_feature_extract_unsigned_field(read_system_reg(SYS_ID_AA64DFR0_EL1),
38 						ID_AA64DFR0_DEBUGVER_SHIFT);
39 }
40 
41 /*
42  * MDSCR access routines.
43  */
44 static void mdscr_write(u32 mdscr)
45 {
46 	unsigned long flags;
47 	local_dbg_save(flags);
48 	asm volatile("msr mdscr_el1, %0" :: "r" (mdscr));
49 	local_dbg_restore(flags);
50 }
51 
52 static u32 mdscr_read(void)
53 {
54 	u32 mdscr;
55 	asm volatile("mrs %0, mdscr_el1" : "=r" (mdscr));
56 	return mdscr;
57 }
58 
59 /*
60  * Allow root to disable self-hosted debug from userspace.
61  * This is useful if you want to connect an external JTAG debugger.
62  */
63 static bool debug_enabled = true;
64 
65 static int create_debug_debugfs_entry(void)
66 {
67 	debugfs_create_bool("debug_enabled", 0644, NULL, &debug_enabled);
68 	return 0;
69 }
70 fs_initcall(create_debug_debugfs_entry);
71 
72 static int __init early_debug_disable(char *buf)
73 {
74 	debug_enabled = false;
75 	return 0;
76 }
77 
78 early_param("nodebugmon", early_debug_disable);
79 
80 /*
81  * Keep track of debug users on each core.
82  * The ref counts are per-cpu so we use a local_t type.
83  */
84 static DEFINE_PER_CPU(int, mde_ref_count);
85 static DEFINE_PER_CPU(int, kde_ref_count);
86 
87 void enable_debug_monitors(enum dbg_active_el el)
88 {
89 	u32 mdscr, enable = 0;
90 
91 	WARN_ON(preemptible());
92 
93 	if (this_cpu_inc_return(mde_ref_count) == 1)
94 		enable = DBG_MDSCR_MDE;
95 
96 	if (el == DBG_ACTIVE_EL1 &&
97 	    this_cpu_inc_return(kde_ref_count) == 1)
98 		enable |= DBG_MDSCR_KDE;
99 
100 	if (enable && debug_enabled) {
101 		mdscr = mdscr_read();
102 		mdscr |= enable;
103 		mdscr_write(mdscr);
104 	}
105 }
106 
107 void disable_debug_monitors(enum dbg_active_el el)
108 {
109 	u32 mdscr, disable = 0;
110 
111 	WARN_ON(preemptible());
112 
113 	if (this_cpu_dec_return(mde_ref_count) == 0)
114 		disable = ~DBG_MDSCR_MDE;
115 
116 	if (el == DBG_ACTIVE_EL1 &&
117 	    this_cpu_dec_return(kde_ref_count) == 0)
118 		disable &= ~DBG_MDSCR_KDE;
119 
120 	if (disable) {
121 		mdscr = mdscr_read();
122 		mdscr &= disable;
123 		mdscr_write(mdscr);
124 	}
125 }
126 
127 /*
128  * OS lock clearing.
129  */
130 static void clear_os_lock(void *unused)
131 {
132 	asm volatile("msr oslar_el1, %0" : : "r" (0));
133 }
134 
135 static int os_lock_notify(struct notifier_block *self,
136 				    unsigned long action, void *data)
137 {
138 	if ((action & ~CPU_TASKS_FROZEN) == CPU_ONLINE)
139 		clear_os_lock(NULL);
140 	return NOTIFY_OK;
141 }
142 
143 static struct notifier_block os_lock_nb = {
144 	.notifier_call = os_lock_notify,
145 };
146 
147 static int debug_monitors_init(void)
148 {
149 	cpu_notifier_register_begin();
150 
151 	/* Clear the OS lock. */
152 	on_each_cpu(clear_os_lock, NULL, 1);
153 	isb();
154 	local_dbg_enable();
155 
156 	/* Register hotplug handler. */
157 	__register_cpu_notifier(&os_lock_nb);
158 
159 	cpu_notifier_register_done();
160 	return 0;
161 }
162 postcore_initcall(debug_monitors_init);
163 
164 /*
165  * Single step API and exception handling.
166  */
167 static void set_regs_spsr_ss(struct pt_regs *regs)
168 {
169 	unsigned long spsr;
170 
171 	spsr = regs->pstate;
172 	spsr &= ~DBG_SPSR_SS;
173 	spsr |= DBG_SPSR_SS;
174 	regs->pstate = spsr;
175 }
176 
177 static void clear_regs_spsr_ss(struct pt_regs *regs)
178 {
179 	unsigned long spsr;
180 
181 	spsr = regs->pstate;
182 	spsr &= ~DBG_SPSR_SS;
183 	regs->pstate = spsr;
184 }
185 
186 /* EL1 Single Step Handler hooks */
187 static LIST_HEAD(step_hook);
188 static DEFINE_SPINLOCK(step_hook_lock);
189 
190 void register_step_hook(struct step_hook *hook)
191 {
192 	spin_lock(&step_hook_lock);
193 	list_add_rcu(&hook->node, &step_hook);
194 	spin_unlock(&step_hook_lock);
195 }
196 
197 void unregister_step_hook(struct step_hook *hook)
198 {
199 	spin_lock(&step_hook_lock);
200 	list_del_rcu(&hook->node);
201 	spin_unlock(&step_hook_lock);
202 	synchronize_rcu();
203 }
204 
205 /*
206  * Call registered single step handlers
207  * There is no Syndrome info to check for determining the handler.
208  * So we call all the registered handlers, until the right handler is
209  * found which returns zero.
210  */
211 static int call_step_hook(struct pt_regs *regs, unsigned int esr)
212 {
213 	struct step_hook *hook;
214 	int retval = DBG_HOOK_ERROR;
215 
216 	rcu_read_lock();
217 
218 	list_for_each_entry_rcu(hook, &step_hook, node)	{
219 		retval = hook->fn(regs, esr);
220 		if (retval == DBG_HOOK_HANDLED)
221 			break;
222 	}
223 
224 	rcu_read_unlock();
225 
226 	return retval;
227 }
228 
229 static void send_user_sigtrap(int si_code)
230 {
231 	struct pt_regs *regs = current_pt_regs();
232 	siginfo_t info = {
233 		.si_signo	= SIGTRAP,
234 		.si_errno	= 0,
235 		.si_code	= si_code,
236 		.si_addr	= (void __user *)instruction_pointer(regs),
237 	};
238 
239 	if (WARN_ON(!user_mode(regs)))
240 		return;
241 
242 	if (interrupts_enabled(regs))
243 		local_irq_enable();
244 
245 	force_sig_info(SIGTRAP, &info, current);
246 }
247 
248 static int single_step_handler(unsigned long addr, unsigned int esr,
249 			       struct pt_regs *regs)
250 {
251 	/*
252 	 * If we are stepping a pending breakpoint, call the hw_breakpoint
253 	 * handler first.
254 	 */
255 	if (!reinstall_suspended_bps(regs))
256 		return 0;
257 
258 	if (user_mode(regs)) {
259 		send_user_sigtrap(TRAP_HWBKPT);
260 
261 		/*
262 		 * ptrace will disable single step unless explicitly
263 		 * asked to re-enable it. For other clients, it makes
264 		 * sense to leave it enabled (i.e. rewind the controls
265 		 * to the active-not-pending state).
266 		 */
267 		user_rewind_single_step(current);
268 	} else {
269 		if (call_step_hook(regs, esr) == DBG_HOOK_HANDLED)
270 			return 0;
271 
272 		pr_warning("Unexpected kernel single-step exception at EL1\n");
273 		/*
274 		 * Re-enable stepping since we know that we will be
275 		 * returning to regs.
276 		 */
277 		set_regs_spsr_ss(regs);
278 	}
279 
280 	return 0;
281 }
282 
283 /*
284  * Breakpoint handler is re-entrant as another breakpoint can
285  * hit within breakpoint handler, especically in kprobes.
286  * Use reader/writer locks instead of plain spinlock.
287  */
288 static LIST_HEAD(break_hook);
289 static DEFINE_SPINLOCK(break_hook_lock);
290 
291 void register_break_hook(struct break_hook *hook)
292 {
293 	spin_lock(&break_hook_lock);
294 	list_add_rcu(&hook->node, &break_hook);
295 	spin_unlock(&break_hook_lock);
296 }
297 
298 void unregister_break_hook(struct break_hook *hook)
299 {
300 	spin_lock(&break_hook_lock);
301 	list_del_rcu(&hook->node);
302 	spin_unlock(&break_hook_lock);
303 	synchronize_rcu();
304 }
305 
306 static int call_break_hook(struct pt_regs *regs, unsigned int esr)
307 {
308 	struct break_hook *hook;
309 	int (*fn)(struct pt_regs *regs, unsigned int esr) = NULL;
310 
311 	rcu_read_lock();
312 	list_for_each_entry_rcu(hook, &break_hook, node)
313 		if ((esr & hook->esr_mask) == hook->esr_val)
314 			fn = hook->fn;
315 	rcu_read_unlock();
316 
317 	return fn ? fn(regs, esr) : DBG_HOOK_ERROR;
318 }
319 
320 static int brk_handler(unsigned long addr, unsigned int esr,
321 		       struct pt_regs *regs)
322 {
323 	if (user_mode(regs)) {
324 		send_user_sigtrap(TRAP_BRKPT);
325 	} else if (call_break_hook(regs, esr) != DBG_HOOK_HANDLED) {
326 		pr_warning("Unexpected kernel BRK exception at EL1\n");
327 		return -EFAULT;
328 	}
329 
330 	return 0;
331 }
332 
333 int aarch32_break_handler(struct pt_regs *regs)
334 {
335 	u32 arm_instr;
336 	u16 thumb_instr;
337 	bool bp = false;
338 	void __user *pc = (void __user *)instruction_pointer(regs);
339 
340 	if (!compat_user_mode(regs))
341 		return -EFAULT;
342 
343 	if (compat_thumb_mode(regs)) {
344 		/* get 16-bit Thumb instruction */
345 		get_user(thumb_instr, (u16 __user *)pc);
346 		thumb_instr = le16_to_cpu(thumb_instr);
347 		if (thumb_instr == AARCH32_BREAK_THUMB2_LO) {
348 			/* get second half of 32-bit Thumb-2 instruction */
349 			get_user(thumb_instr, (u16 __user *)(pc + 2));
350 			thumb_instr = le16_to_cpu(thumb_instr);
351 			bp = thumb_instr == AARCH32_BREAK_THUMB2_HI;
352 		} else {
353 			bp = thumb_instr == AARCH32_BREAK_THUMB;
354 		}
355 	} else {
356 		/* 32-bit ARM instruction */
357 		get_user(arm_instr, (u32 __user *)pc);
358 		arm_instr = le32_to_cpu(arm_instr);
359 		bp = (arm_instr & ~0xf0000000) == AARCH32_BREAK_ARM;
360 	}
361 
362 	if (!bp)
363 		return -EFAULT;
364 
365 	send_user_sigtrap(TRAP_BRKPT);
366 	return 0;
367 }
368 
369 static int __init debug_traps_init(void)
370 {
371 	hook_debug_fault_code(DBG_ESR_EVT_HWSS, single_step_handler, SIGTRAP,
372 			      TRAP_HWBKPT, "single-step handler");
373 	hook_debug_fault_code(DBG_ESR_EVT_BRK, brk_handler, SIGTRAP,
374 			      TRAP_BRKPT, "ptrace BRK handler");
375 	return 0;
376 }
377 arch_initcall(debug_traps_init);
378 
379 /* Re-enable single step for syscall restarting. */
380 void user_rewind_single_step(struct task_struct *task)
381 {
382 	/*
383 	 * If single step is active for this thread, then set SPSR.SS
384 	 * to 1 to avoid returning to the active-pending state.
385 	 */
386 	if (test_ti_thread_flag(task_thread_info(task), TIF_SINGLESTEP))
387 		set_regs_spsr_ss(task_pt_regs(task));
388 }
389 
390 void user_fastforward_single_step(struct task_struct *task)
391 {
392 	if (test_ti_thread_flag(task_thread_info(task), TIF_SINGLESTEP))
393 		clear_regs_spsr_ss(task_pt_regs(task));
394 }
395 
396 /* Kernel API */
397 void kernel_enable_single_step(struct pt_regs *regs)
398 {
399 	WARN_ON(!irqs_disabled());
400 	set_regs_spsr_ss(regs);
401 	mdscr_write(mdscr_read() | DBG_MDSCR_SS);
402 	enable_debug_monitors(DBG_ACTIVE_EL1);
403 }
404 
405 void kernel_disable_single_step(void)
406 {
407 	WARN_ON(!irqs_disabled());
408 	mdscr_write(mdscr_read() & ~DBG_MDSCR_SS);
409 	disable_debug_monitors(DBG_ACTIVE_EL1);
410 }
411 
412 int kernel_active_single_step(void)
413 {
414 	WARN_ON(!irqs_disabled());
415 	return mdscr_read() & DBG_MDSCR_SS;
416 }
417 
418 /* ptrace API */
419 void user_enable_single_step(struct task_struct *task)
420 {
421 	set_ti_thread_flag(task_thread_info(task), TIF_SINGLESTEP);
422 	set_regs_spsr_ss(task_pt_regs(task));
423 }
424 
425 void user_disable_single_step(struct task_struct *task)
426 {
427 	clear_ti_thread_flag(task_thread_info(task), TIF_SINGLESTEP);
428 }
429