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/debug-monitors.h>
30 #include <asm/cputype.h>
31 #include <asm/system_misc.h>
32 
33 /* Low-level stepping controls. */
34 #define DBG_MDSCR_SS		(1 << 0)
35 #define DBG_SPSR_SS		(1 << 21)
36 
37 /* MDSCR_EL1 enabling bits */
38 #define DBG_MDSCR_KDE		(1 << 13)
39 #define DBG_MDSCR_MDE		(1 << 15)
40 #define DBG_MDSCR_MASK		~(DBG_MDSCR_KDE | DBG_MDSCR_MDE)
41 
42 /* Determine debug architecture. */
43 u8 debug_monitors_arch(void)
44 {
45 	return read_cpuid(ID_AA64DFR0_EL1) & 0xf;
46 }
47 
48 /*
49  * MDSCR access routines.
50  */
51 static void mdscr_write(u32 mdscr)
52 {
53 	unsigned long flags;
54 	local_dbg_save(flags);
55 	asm volatile("msr mdscr_el1, %0" :: "r" (mdscr));
56 	local_dbg_restore(flags);
57 }
58 
59 static u32 mdscr_read(void)
60 {
61 	u32 mdscr;
62 	asm volatile("mrs %0, mdscr_el1" : "=r" (mdscr));
63 	return mdscr;
64 }
65 
66 /*
67  * Allow root to disable self-hosted debug from userspace.
68  * This is useful if you want to connect an external JTAG debugger.
69  */
70 static u32 debug_enabled = 1;
71 
72 static int create_debug_debugfs_entry(void)
73 {
74 	debugfs_create_bool("debug_enabled", 0644, NULL, &debug_enabled);
75 	return 0;
76 }
77 fs_initcall(create_debug_debugfs_entry);
78 
79 static int __init early_debug_disable(char *buf)
80 {
81 	debug_enabled = 0;
82 	return 0;
83 }
84 
85 early_param("nodebugmon", early_debug_disable);
86 
87 /*
88  * Keep track of debug users on each core.
89  * The ref counts are per-cpu so we use a local_t type.
90  */
91 static DEFINE_PER_CPU(int, mde_ref_count);
92 static DEFINE_PER_CPU(int, kde_ref_count);
93 
94 void enable_debug_monitors(enum debug_el el)
95 {
96 	u32 mdscr, enable = 0;
97 
98 	WARN_ON(preemptible());
99 
100 	if (this_cpu_inc_return(mde_ref_count) == 1)
101 		enable = DBG_MDSCR_MDE;
102 
103 	if (el == DBG_ACTIVE_EL1 &&
104 	    this_cpu_inc_return(kde_ref_count) == 1)
105 		enable |= DBG_MDSCR_KDE;
106 
107 	if (enable && debug_enabled) {
108 		mdscr = mdscr_read();
109 		mdscr |= enable;
110 		mdscr_write(mdscr);
111 	}
112 }
113 
114 void disable_debug_monitors(enum debug_el el)
115 {
116 	u32 mdscr, disable = 0;
117 
118 	WARN_ON(preemptible());
119 
120 	if (this_cpu_dec_return(mde_ref_count) == 0)
121 		disable = ~DBG_MDSCR_MDE;
122 
123 	if (el == DBG_ACTIVE_EL1 &&
124 	    this_cpu_dec_return(kde_ref_count) == 0)
125 		disable &= ~DBG_MDSCR_KDE;
126 
127 	if (disable) {
128 		mdscr = mdscr_read();
129 		mdscr &= disable;
130 		mdscr_write(mdscr);
131 	}
132 }
133 
134 /*
135  * OS lock clearing.
136  */
137 static void clear_os_lock(void *unused)
138 {
139 	asm volatile("msr oslar_el1, %0" : : "r" (0));
140 	isb();
141 }
142 
143 static int os_lock_notify(struct notifier_block *self,
144 				    unsigned long action, void *data)
145 {
146 	int cpu = (unsigned long)data;
147 	if (action == CPU_ONLINE)
148 		smp_call_function_single(cpu, clear_os_lock, NULL, 1);
149 	return NOTIFY_OK;
150 }
151 
152 static struct notifier_block os_lock_nb = {
153 	.notifier_call = os_lock_notify,
154 };
155 
156 static int debug_monitors_init(void)
157 {
158 	/* Clear the OS lock. */
159 	smp_call_function(clear_os_lock, NULL, 1);
160 	clear_os_lock(NULL);
161 
162 	/* Register hotplug handler. */
163 	register_cpu_notifier(&os_lock_nb);
164 	return 0;
165 }
166 postcore_initcall(debug_monitors_init);
167 
168 /*
169  * Single step API and exception handling.
170  */
171 static void set_regs_spsr_ss(struct pt_regs *regs)
172 {
173 	unsigned long spsr;
174 
175 	spsr = regs->pstate;
176 	spsr &= ~DBG_SPSR_SS;
177 	spsr |= DBG_SPSR_SS;
178 	regs->pstate = spsr;
179 }
180 
181 static void clear_regs_spsr_ss(struct pt_regs *regs)
182 {
183 	unsigned long spsr;
184 
185 	spsr = regs->pstate;
186 	spsr &= ~DBG_SPSR_SS;
187 	regs->pstate = spsr;
188 }
189 
190 static int single_step_handler(unsigned long addr, unsigned int esr,
191 			       struct pt_regs *regs)
192 {
193 	siginfo_t info;
194 
195 	/*
196 	 * If we are stepping a pending breakpoint, call the hw_breakpoint
197 	 * handler first.
198 	 */
199 	if (!reinstall_suspended_bps(regs))
200 		return 0;
201 
202 	if (user_mode(regs)) {
203 		info.si_signo = SIGTRAP;
204 		info.si_errno = 0;
205 		info.si_code  = TRAP_HWBKPT;
206 		info.si_addr  = (void __user *)instruction_pointer(regs);
207 		force_sig_info(SIGTRAP, &info, current);
208 
209 		/*
210 		 * ptrace will disable single step unless explicitly
211 		 * asked to re-enable it. For other clients, it makes
212 		 * sense to leave it enabled (i.e. rewind the controls
213 		 * to the active-not-pending state).
214 		 */
215 		user_rewind_single_step(current);
216 	} else {
217 		/* TODO: route to KGDB */
218 		pr_warning("Unexpected kernel single-step exception at EL1\n");
219 		/*
220 		 * Re-enable stepping since we know that we will be
221 		 * returning to regs.
222 		 */
223 		set_regs_spsr_ss(regs);
224 	}
225 
226 	return 0;
227 }
228 
229 static int brk_handler(unsigned long addr, unsigned int esr,
230 		       struct pt_regs *regs)
231 {
232 	siginfo_t info;
233 
234 	if (!user_mode(regs))
235 		return -EFAULT;
236 
237 	info = (siginfo_t) {
238 		.si_signo = SIGTRAP,
239 		.si_errno = 0,
240 		.si_code  = TRAP_BRKPT,
241 		.si_addr  = (void __user *)instruction_pointer(regs),
242 	};
243 
244 	force_sig_info(SIGTRAP, &info, current);
245 	return 0;
246 }
247 
248 int aarch32_break_handler(struct pt_regs *regs)
249 {
250 	siginfo_t info;
251 	u32 arm_instr;
252 	u16 thumb_instr;
253 	bool bp = false;
254 	void __user *pc = (void __user *)instruction_pointer(regs);
255 
256 	if (!compat_user_mode(regs))
257 		return -EFAULT;
258 
259 	if (compat_thumb_mode(regs)) {
260 		/* get 16-bit Thumb instruction */
261 		get_user(thumb_instr, (u16 __user *)pc);
262 		thumb_instr = le16_to_cpu(thumb_instr);
263 		if (thumb_instr == AARCH32_BREAK_THUMB2_LO) {
264 			/* get second half of 32-bit Thumb-2 instruction */
265 			get_user(thumb_instr, (u16 __user *)(pc + 2));
266 			thumb_instr = le16_to_cpu(thumb_instr);
267 			bp = thumb_instr == AARCH32_BREAK_THUMB2_HI;
268 		} else {
269 			bp = thumb_instr == AARCH32_BREAK_THUMB;
270 		}
271 	} else {
272 		/* 32-bit ARM instruction */
273 		get_user(arm_instr, (u32 __user *)pc);
274 		arm_instr = le32_to_cpu(arm_instr);
275 		bp = (arm_instr & ~0xf0000000) == AARCH32_BREAK_ARM;
276 	}
277 
278 	if (!bp)
279 		return -EFAULT;
280 
281 	info = (siginfo_t) {
282 		.si_signo = SIGTRAP,
283 		.si_errno = 0,
284 		.si_code  = TRAP_BRKPT,
285 		.si_addr  = pc,
286 	};
287 
288 	force_sig_info(SIGTRAP, &info, current);
289 	return 0;
290 }
291 
292 static int __init debug_traps_init(void)
293 {
294 	hook_debug_fault_code(DBG_ESR_EVT_HWSS, single_step_handler, SIGTRAP,
295 			      TRAP_HWBKPT, "single-step handler");
296 	hook_debug_fault_code(DBG_ESR_EVT_BRK, brk_handler, SIGTRAP,
297 			      TRAP_BRKPT, "ptrace BRK handler");
298 	return 0;
299 }
300 arch_initcall(debug_traps_init);
301 
302 /* Re-enable single step for syscall restarting. */
303 void user_rewind_single_step(struct task_struct *task)
304 {
305 	/*
306 	 * If single step is active for this thread, then set SPSR.SS
307 	 * to 1 to avoid returning to the active-pending state.
308 	 */
309 	if (test_ti_thread_flag(task_thread_info(task), TIF_SINGLESTEP))
310 		set_regs_spsr_ss(task_pt_regs(task));
311 }
312 
313 void user_fastforward_single_step(struct task_struct *task)
314 {
315 	if (test_ti_thread_flag(task_thread_info(task), TIF_SINGLESTEP))
316 		clear_regs_spsr_ss(task_pt_regs(task));
317 }
318 
319 /* Kernel API */
320 void kernel_enable_single_step(struct pt_regs *regs)
321 {
322 	WARN_ON(!irqs_disabled());
323 	set_regs_spsr_ss(regs);
324 	mdscr_write(mdscr_read() | DBG_MDSCR_SS);
325 	enable_debug_monitors(DBG_ACTIVE_EL1);
326 }
327 
328 void kernel_disable_single_step(void)
329 {
330 	WARN_ON(!irqs_disabled());
331 	mdscr_write(mdscr_read() & ~DBG_MDSCR_SS);
332 	disable_debug_monitors(DBG_ACTIVE_EL1);
333 }
334 
335 int kernel_active_single_step(void)
336 {
337 	WARN_ON(!irqs_disabled());
338 	return mdscr_read() & DBG_MDSCR_SS;
339 }
340 
341 /* ptrace API */
342 void user_enable_single_step(struct task_struct *task)
343 {
344 	set_ti_thread_flag(task_thread_info(task), TIF_SINGLESTEP);
345 	set_regs_spsr_ss(task_pt_regs(task));
346 }
347 
348 void user_disable_single_step(struct task_struct *task)
349 {
350 	clear_ti_thread_flag(task_thread_info(task), TIF_SINGLESTEP);
351 }
352