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. */
 35u8 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 */
 44static 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
 52static 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 */
 63static bool debug_enabled = true;
 64
 65static int create_debug_debugfs_entry(void)
 66{
 67	debugfs_create_bool("debug_enabled", 0644, NULL, &debug_enabled);
 68	return 0;
 69}
 70fs_initcall(create_debug_debugfs_entry);
 71
 72static int __init early_debug_disable(char *buf)
 73{
 74	debug_enabled = false;
 75	return 0;
 76}
 77
 78early_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 */
 84static DEFINE_PER_CPU(int, mde_ref_count);
 85static DEFINE_PER_CPU(int, kde_ref_count);
 86
 87void 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
107void 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 */
130static void clear_os_lock(void *unused)
131{
132	asm volatile("msr oslar_el1, %0" : : "r" (0));
133}
134
135static 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
144static struct notifier_block os_lock_nb = {
145	.notifier_call = os_lock_notify,
146};
147
148static 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}
163postcore_initcall(debug_monitors_init);
164
165/*
166 * Single step API and exception handling.
167 */
168static 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
178static 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 */
188static LIST_HEAD(step_hook);
189static DEFINE_SPINLOCK(step_hook_lock);
190
191void register_step_hook(struct step_hook *hook)
192{
193	spin_lock(&step_hook_lock);
194	list_add_rcu(&hook->node, &step_hook);
195	spin_unlock(&step_hook_lock);
196}
197
198void unregister_step_hook(struct step_hook *hook)
199{
200	spin_lock(&step_hook_lock);
201	list_del_rcu(&hook->node);
202	spin_unlock(&step_hook_lock);
203	synchronize_rcu();
204}
205
206/*
207 * Call registered single step handlers
208 * There is no Syndrome info to check for determining the handler.
209 * So we call all the registered handlers, until the right handler is
210 * found which returns zero.
211 */
212static int call_step_hook(struct pt_regs *regs, unsigned int esr)
213{
214	struct step_hook *hook;
215	int retval = DBG_HOOK_ERROR;
216
217	rcu_read_lock();
218
219	list_for_each_entry_rcu(hook, &step_hook, node)	{
220		retval = hook->fn(regs, esr);
221		if (retval == DBG_HOOK_HANDLED)
222			break;
223	}
224
225	rcu_read_unlock();
226
227	return retval;
228}
229
230static void send_user_sigtrap(int si_code)
231{
232	struct pt_regs *regs = current_pt_regs();
233	siginfo_t info = {
234		.si_signo	= SIGTRAP,
235		.si_errno	= 0,
236		.si_code	= si_code,
237		.si_addr	= (void __user *)instruction_pointer(regs),
238	};
239
240	if (WARN_ON(!user_mode(regs)))
241		return;
242
243	if (interrupts_enabled(regs))
244		local_irq_enable();
245
246	force_sig_info(SIGTRAP, &info, current);
247}
248
249static int single_step_handler(unsigned long addr, unsigned int esr,
250			       struct pt_regs *regs)
251{
252	/*
253	 * If we are stepping a pending breakpoint, call the hw_breakpoint
254	 * handler first.
255	 */
256	if (!reinstall_suspended_bps(regs))
257		return 0;
258
259	if (user_mode(regs)) {
260		send_user_sigtrap(TRAP_HWBKPT);
261
262		/*
263		 * ptrace will disable single step unless explicitly
264		 * asked to re-enable it. For other clients, it makes
265		 * sense to leave it enabled (i.e. rewind the controls
266		 * to the active-not-pending state).
267		 */
268		user_rewind_single_step(current);
269	} else {
270		if (call_step_hook(regs, esr) == DBG_HOOK_HANDLED)
271			return 0;
272
273		pr_warning("Unexpected kernel single-step exception at EL1\n");
274		/*
275		 * Re-enable stepping since we know that we will be
276		 * returning to regs.
277		 */
278		set_regs_spsr_ss(regs);
279	}
280
281	return 0;
282}
283
284/*
285 * Breakpoint handler is re-entrant as another breakpoint can
286 * hit within breakpoint handler, especically in kprobes.
287 * Use reader/writer locks instead of plain spinlock.
288 */
289static LIST_HEAD(break_hook);
290static DEFINE_SPINLOCK(break_hook_lock);
291
292void register_break_hook(struct break_hook *hook)
293{
294	spin_lock(&break_hook_lock);
295	list_add_rcu(&hook->node, &break_hook);
296	spin_unlock(&break_hook_lock);
297}
298
299void unregister_break_hook(struct break_hook *hook)
300{
301	spin_lock(&break_hook_lock);
302	list_del_rcu(&hook->node);
303	spin_unlock(&break_hook_lock);
304	synchronize_rcu();
305}
306
307static int call_break_hook(struct pt_regs *regs, unsigned int esr)
308{
309	struct break_hook *hook;
310	int (*fn)(struct pt_regs *regs, unsigned int esr) = NULL;
311
312	rcu_read_lock();
313	list_for_each_entry_rcu(hook, &break_hook, node)
314		if ((esr & hook->esr_mask) == hook->esr_val)
315			fn = hook->fn;
316	rcu_read_unlock();
317
318	return fn ? fn(regs, esr) : DBG_HOOK_ERROR;
319}
320
321static int brk_handler(unsigned long addr, unsigned int esr,
322		       struct pt_regs *regs)
323{
324	if (user_mode(regs)) {
325		send_user_sigtrap(TRAP_BRKPT);
326	} else if (call_break_hook(regs, esr) != DBG_HOOK_HANDLED) {
327		pr_warning("Unexpected kernel BRK exception at EL1\n");
328		return -EFAULT;
329	}
330
331	return 0;
332}
333
334int aarch32_break_handler(struct pt_regs *regs)
335{
336	u32 arm_instr;
337	u16 thumb_instr;
338	bool bp = false;
339	void __user *pc = (void __user *)instruction_pointer(regs);
340
341	if (!compat_user_mode(regs))
342		return -EFAULT;
343
344	if (compat_thumb_mode(regs)) {
345		/* get 16-bit Thumb instruction */
346		get_user(thumb_instr, (u16 __user *)pc);
347		thumb_instr = le16_to_cpu(thumb_instr);
348		if (thumb_instr == AARCH32_BREAK_THUMB2_LO) {
349			/* get second half of 32-bit Thumb-2 instruction */
350			get_user(thumb_instr, (u16 __user *)(pc + 2));
351			thumb_instr = le16_to_cpu(thumb_instr);
352			bp = thumb_instr == AARCH32_BREAK_THUMB2_HI;
353		} else {
354			bp = thumb_instr == AARCH32_BREAK_THUMB;
355		}
356	} else {
357		/* 32-bit ARM instruction */
358		get_user(arm_instr, (u32 __user *)pc);
359		arm_instr = le32_to_cpu(arm_instr);
360		bp = (arm_instr & ~0xf0000000) == AARCH32_BREAK_ARM;
361	}
362
363	if (!bp)
364		return -EFAULT;
365
366	send_user_sigtrap(TRAP_BRKPT);
367	return 0;
368}
369
370static int __init debug_traps_init(void)
371{
372	hook_debug_fault_code(DBG_ESR_EVT_HWSS, single_step_handler, SIGTRAP,
373			      TRAP_HWBKPT, "single-step handler");
374	hook_debug_fault_code(DBG_ESR_EVT_BRK, brk_handler, SIGTRAP,
375			      TRAP_BRKPT, "ptrace BRK handler");
376	return 0;
377}
378arch_initcall(debug_traps_init);
379
380/* Re-enable single step for syscall restarting. */
381void user_rewind_single_step(struct task_struct *task)
382{
383	/*
384	 * If single step is active for this thread, then set SPSR.SS
385	 * to 1 to avoid returning to the active-pending state.
386	 */
387	if (test_ti_thread_flag(task_thread_info(task), TIF_SINGLESTEP))
388		set_regs_spsr_ss(task_pt_regs(task));
389}
390
391void user_fastforward_single_step(struct task_struct *task)
392{
393	if (test_ti_thread_flag(task_thread_info(task), TIF_SINGLESTEP))
394		clear_regs_spsr_ss(task_pt_regs(task));
395}
396
397/* Kernel API */
398void kernel_enable_single_step(struct pt_regs *regs)
399{
400	WARN_ON(!irqs_disabled());
401	set_regs_spsr_ss(regs);
402	mdscr_write(mdscr_read() | DBG_MDSCR_SS);
403	enable_debug_monitors(DBG_ACTIVE_EL1);
404}
405
406void kernel_disable_single_step(void)
407{
408	WARN_ON(!irqs_disabled());
409	mdscr_write(mdscr_read() & ~DBG_MDSCR_SS);
410	disable_debug_monitors(DBG_ACTIVE_EL1);
411}
412
413int kernel_active_single_step(void)
414{
415	WARN_ON(!irqs_disabled());
416	return mdscr_read() & DBG_MDSCR_SS;
417}
418
419/* ptrace API */
420void user_enable_single_step(struct task_struct *task)
421{
422	set_ti_thread_flag(task_thread_info(task), TIF_SINGLESTEP);
423	set_regs_spsr_ss(task_pt_regs(task));
424}
425
426void user_disable_single_step(struct task_struct *task)
427{
428	clear_ti_thread_flag(task_thread_info(task), TIF_SINGLESTEP);
429}