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_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 	int cpu = (unsigned long)data;
139 	if ((action & ~CPU_TASKS_FROZEN) == CPU_ONLINE)
140 		smp_call_function_single(cpu, clear_os_lock, NULL, 1);
141 	return NOTIFY_OK;
142 }
143 
144 static struct notifier_block os_lock_nb = {
145 	.notifier_call = os_lock_notify,
146 };
147 
148 static int debug_monitors_init(void)
149 {
150 	cpu_notifier_register_begin();
151 
152 	/* Clear the OS lock. */
153 	on_each_cpu(clear_os_lock, NULL, 1);
154 	isb();
155 	local_dbg_enable();
156 
157 	/* Register hotplug handler. */
158 	__register_cpu_notifier(&os_lock_nb);
159 
160 	cpu_notifier_register_done();
161 	return 0;
162 }
163 postcore_initcall(debug_monitors_init);
164 
165 /*
166  * Single step API and exception handling.
167  */
168 static void set_regs_spsr_ss(struct pt_regs *regs)
169 {
170 	unsigned long spsr;
171 
172 	spsr = regs->pstate;
173 	spsr &= ~DBG_SPSR_SS;
174 	spsr |= DBG_SPSR_SS;
175 	regs->pstate = spsr;
176 }
177 
178 static void clear_regs_spsr_ss(struct pt_regs *regs)
179 {
180 	unsigned long spsr;
181 
182 	spsr = regs->pstate;
183 	spsr &= ~DBG_SPSR_SS;
184 	regs->pstate = spsr;
185 }
186 
187 /* EL1 Single Step Handler hooks */
188 static LIST_HEAD(step_hook);
189 static DEFINE_RWLOCK(step_hook_lock);
190 
191 void register_step_hook(struct step_hook *hook)
192 {
193 	write_lock(&step_hook_lock);
194 	list_add(&hook->node, &step_hook);
195 	write_unlock(&step_hook_lock);
196 }
197 
198 void unregister_step_hook(struct step_hook *hook)
199 {
200 	write_lock(&step_hook_lock);
201 	list_del(&hook->node);
202 	write_unlock(&step_hook_lock);
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 	read_lock(&step_hook_lock);
217 
218 	list_for_each_entry(hook, &step_hook, node)	{
219 		retval = hook->fn(regs, esr);
220 		if (retval == DBG_HOOK_HANDLED)
221 			break;
222 	}
223 
224 	read_unlock(&step_hook_lock);
225 
226 	return retval;
227 }
228 
229 static int single_step_handler(unsigned long addr, unsigned int esr,
230 			       struct pt_regs *regs)
231 {
232 	siginfo_t info;
233 
234 	/*
235 	 * If we are stepping a pending breakpoint, call the hw_breakpoint
236 	 * handler first.
237 	 */
238 	if (!reinstall_suspended_bps(regs))
239 		return 0;
240 
241 	if (user_mode(regs)) {
242 		info.si_signo = SIGTRAP;
243 		info.si_errno = 0;
244 		info.si_code  = TRAP_HWBKPT;
245 		info.si_addr  = (void __user *)instruction_pointer(regs);
246 		force_sig_info(SIGTRAP, &info, current);
247 
248 		/*
249 		 * ptrace will disable single step unless explicitly
250 		 * asked to re-enable it. For other clients, it makes
251 		 * sense to leave it enabled (i.e. rewind the controls
252 		 * to the active-not-pending state).
253 		 */
254 		user_rewind_single_step(current);
255 	} else {
256 		if (call_step_hook(regs, esr) == DBG_HOOK_HANDLED)
257 			return 0;
258 
259 		pr_warning("Unexpected kernel single-step exception at EL1\n");
260 		/*
261 		 * Re-enable stepping since we know that we will be
262 		 * returning to regs.
263 		 */
264 		set_regs_spsr_ss(regs);
265 	}
266 
267 	return 0;
268 }
269 
270 /*
271  * Breakpoint handler is re-entrant as another breakpoint can
272  * hit within breakpoint handler, especically in kprobes.
273  * Use reader/writer locks instead of plain spinlock.
274  */
275 static LIST_HEAD(break_hook);
276 static DEFINE_SPINLOCK(break_hook_lock);
277 
278 void register_break_hook(struct break_hook *hook)
279 {
280 	spin_lock(&break_hook_lock);
281 	list_add_rcu(&hook->node, &break_hook);
282 	spin_unlock(&break_hook_lock);
283 }
284 
285 void unregister_break_hook(struct break_hook *hook)
286 {
287 	spin_lock(&break_hook_lock);
288 	list_del_rcu(&hook->node);
289 	spin_unlock(&break_hook_lock);
290 	synchronize_rcu();
291 }
292 
293 static int call_break_hook(struct pt_regs *regs, unsigned int esr)
294 {
295 	struct break_hook *hook;
296 	int (*fn)(struct pt_regs *regs, unsigned int esr) = NULL;
297 
298 	rcu_read_lock();
299 	list_for_each_entry_rcu(hook, &break_hook, node)
300 		if ((esr & hook->esr_mask) == hook->esr_val)
301 			fn = hook->fn;
302 	rcu_read_unlock();
303 
304 	return fn ? fn(regs, esr) : DBG_HOOK_ERROR;
305 }
306 
307 static int brk_handler(unsigned long addr, unsigned int esr,
308 		       struct pt_regs *regs)
309 {
310 	siginfo_t info;
311 
312 	if (user_mode(regs)) {
313 		info = (siginfo_t) {
314 			.si_signo = SIGTRAP,
315 			.si_errno = 0,
316 			.si_code  = TRAP_BRKPT,
317 			.si_addr  = (void __user *)instruction_pointer(regs),
318 		};
319 
320 		force_sig_info(SIGTRAP, &info, current);
321 	} else if (call_break_hook(regs, esr) != DBG_HOOK_HANDLED) {
322 		pr_warning("Unexpected kernel BRK exception at EL1\n");
323 		return -EFAULT;
324 	}
325 
326 	return 0;
327 }
328 
329 int aarch32_break_handler(struct pt_regs *regs)
330 {
331 	siginfo_t info;
332 	u32 arm_instr;
333 	u16 thumb_instr;
334 	bool bp = false;
335 	void __user *pc = (void __user *)instruction_pointer(regs);
336 
337 	if (!compat_user_mode(regs))
338 		return -EFAULT;
339 
340 	if (compat_thumb_mode(regs)) {
341 		/* get 16-bit Thumb instruction */
342 		get_user(thumb_instr, (u16 __user *)pc);
343 		thumb_instr = le16_to_cpu(thumb_instr);
344 		if (thumb_instr == AARCH32_BREAK_THUMB2_LO) {
345 			/* get second half of 32-bit Thumb-2 instruction */
346 			get_user(thumb_instr, (u16 __user *)(pc + 2));
347 			thumb_instr = le16_to_cpu(thumb_instr);
348 			bp = thumb_instr == AARCH32_BREAK_THUMB2_HI;
349 		} else {
350 			bp = thumb_instr == AARCH32_BREAK_THUMB;
351 		}
352 	} else {
353 		/* 32-bit ARM instruction */
354 		get_user(arm_instr, (u32 __user *)pc);
355 		arm_instr = le32_to_cpu(arm_instr);
356 		bp = (arm_instr & ~0xf0000000) == AARCH32_BREAK_ARM;
357 	}
358 
359 	if (!bp)
360 		return -EFAULT;
361 
362 	info = (siginfo_t) {
363 		.si_signo = SIGTRAP,
364 		.si_errno = 0,
365 		.si_code  = TRAP_BRKPT,
366 		.si_addr  = pc,
367 	};
368 
369 	force_sig_info(SIGTRAP, &info, current);
370 	return 0;
371 }
372 
373 static int __init debug_traps_init(void)
374 {
375 	hook_debug_fault_code(DBG_ESR_EVT_HWSS, single_step_handler, SIGTRAP,
376 			      TRAP_HWBKPT, "single-step handler");
377 	hook_debug_fault_code(DBG_ESR_EVT_BRK, brk_handler, SIGTRAP,
378 			      TRAP_BRKPT, "ptrace BRK handler");
379 	return 0;
380 }
381 arch_initcall(debug_traps_init);
382 
383 /* Re-enable single step for syscall restarting. */
384 void user_rewind_single_step(struct task_struct *task)
385 {
386 	/*
387 	 * If single step is active for this thread, then set SPSR.SS
388 	 * to 1 to avoid returning to the active-pending state.
389 	 */
390 	if (test_ti_thread_flag(task_thread_info(task), TIF_SINGLESTEP))
391 		set_regs_spsr_ss(task_pt_regs(task));
392 }
393 
394 void user_fastforward_single_step(struct task_struct *task)
395 {
396 	if (test_ti_thread_flag(task_thread_info(task), TIF_SINGLESTEP))
397 		clear_regs_spsr_ss(task_pt_regs(task));
398 }
399 
400 /* Kernel API */
401 void kernel_enable_single_step(struct pt_regs *regs)
402 {
403 	WARN_ON(!irqs_disabled());
404 	set_regs_spsr_ss(regs);
405 	mdscr_write(mdscr_read() | DBG_MDSCR_SS);
406 	enable_debug_monitors(DBG_ACTIVE_EL1);
407 }
408 
409 void kernel_disable_single_step(void)
410 {
411 	WARN_ON(!irqs_disabled());
412 	mdscr_write(mdscr_read() & ~DBG_MDSCR_SS);
413 	disable_debug_monitors(DBG_ACTIVE_EL1);
414 }
415 
416 int kernel_active_single_step(void)
417 {
418 	WARN_ON(!irqs_disabled());
419 	return mdscr_read() & DBG_MDSCR_SS;
420 }
421 
422 /* ptrace API */
423 void user_enable_single_step(struct task_struct *task)
424 {
425 	set_ti_thread_flag(task_thread_info(task), TIF_SINGLESTEP);
426 	set_regs_spsr_ss(task_pt_regs(task));
427 }
428 
429 void user_disable_single_step(struct task_struct *task)
430 {
431 	clear_ti_thread_flag(task_thread_info(task), TIF_SINGLESTEP);
432 }
433