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Linux/arch/arm64/kernel/debug-monitors.c

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  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. */
 28 u8 debug_monitors_arch(void)
 29 {
 30         return cpuid_feature_extract_unsigned_field(read_sanitised_ftr_reg(SYS_ID_AA64DFR0_EL1),
 31                                                 ID_AA64DFR0_DEBUGVER_SHIFT);
 32 }
 33 
 34 /*
 35  * MDSCR access routines.
 36  */
 37 static 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 }
 44 NOKPROBE_SYMBOL(mdscr_write);
 45 
 46 static u32 mdscr_read(void)
 47 {
 48         return read_sysreg(mdscr_el1);
 49 }
 50 NOKPROBE_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  */
 56 static bool debug_enabled = true;
 57 
 58 static int create_debug_debugfs_entry(void)
 59 {
 60         debugfs_create_bool("debug_enabled", 0644, NULL, &debug_enabled);
 61         return 0;
 62 }
 63 fs_initcall(create_debug_debugfs_entry);
 64 
 65 static int __init early_debug_disable(char *buf)
 66 {
 67         debug_enabled = false;
 68         return 0;
 69 }
 70 
 71 early_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  */
 77 static DEFINE_PER_CPU(int, mde_ref_count);
 78 static DEFINE_PER_CPU(int, kde_ref_count);
 79 
 80 void 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 }
 99 NOKPROBE_SYMBOL(enable_debug_monitors);
100 
101 void 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 }
120 NOKPROBE_SYMBOL(disable_debug_monitors);
121 
122 /*
123  * OS lock clearing.
124  */
125 static 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 
133 static int 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 }
139 postcore_initcall(debug_monitors_init);
140 
141 /*
142  * Single step API and exception handling.
143  */
144 static void set_regs_spsr_ss(struct pt_regs *regs)
145 {
146         regs->pstate |= DBG_SPSR_SS;
147 }
148 NOKPROBE_SYMBOL(set_regs_spsr_ss);
149 
150 static void clear_regs_spsr_ss(struct pt_regs *regs)
151 {
152         regs->pstate &= ~DBG_SPSR_SS;
153 }
154 NOKPROBE_SYMBOL(clear_regs_spsr_ss);
155 
156 static DEFINE_SPINLOCK(debug_hook_lock);
157 static LIST_HEAD(user_step_hook);
158 static LIST_HEAD(kernel_step_hook);
159 
160 static void register_debug_hook(struct list_head *node, struct list_head *list)
161 {
162         spin_lock(&debug_hook_lock);
163         list_add_rcu(node, list);
164         spin_unlock(&debug_hook_lock);
165 
166 }
167 
168 static void unregister_debug_hook(struct list_head *node)
169 {
170         spin_lock(&debug_hook_lock);
171         list_del_rcu(node);
172         spin_unlock(&debug_hook_lock);
173         synchronize_rcu();
174 }
175 
176 void register_user_step_hook(struct step_hook *hook)
177 {
178         register_debug_hook(&hook->node, &user_step_hook);
179 }
180 
181 void unregister_user_step_hook(struct step_hook *hook)
182 {
183         unregister_debug_hook(&hook->node);
184 }
185 
186 void register_kernel_step_hook(struct step_hook *hook)
187 {
188         register_debug_hook(&hook->node, &kernel_step_hook);
189 }
190 
191 void unregister_kernel_step_hook(struct step_hook *hook)
192 {
193         unregister_debug_hook(&hook->node);
194 }
195 
196 /*
197  * Call registered single step handlers
198  * There is no Syndrome info to check for determining the handler.
199  * So we call all the registered handlers, until the right handler is
200  * found which returns zero.
201  */
202 static int call_step_hook(struct pt_regs *regs, unsigned int esr)
203 {
204         struct step_hook *hook;
205         struct list_head *list;
206         int retval = DBG_HOOK_ERROR;
207 
208         list = user_mode(regs) ? &user_step_hook : &kernel_step_hook;
209 
210         /*
211          * Since single-step exception disables interrupt, this function is
212          * entirely not preemptible, and we can use rcu list safely here.
213          */
214         list_for_each_entry_rcu(hook, list, node)       {
215                 retval = hook->fn(regs, esr);
216                 if (retval == DBG_HOOK_HANDLED)
217                         break;
218         }
219 
220         return retval;
221 }
222 NOKPROBE_SYMBOL(call_step_hook);
223 
224 static void send_user_sigtrap(int si_code)
225 {
226         struct pt_regs *regs = current_pt_regs();
227 
228         if (WARN_ON(!user_mode(regs)))
229                 return;
230 
231         if (interrupts_enabled(regs))
232                 local_irq_enable();
233 
234         arm64_force_sig_fault(SIGTRAP, si_code,
235                              (void __user *)instruction_pointer(regs),
236                              "User debug trap");
237 }
238 
239 static int single_step_handler(unsigned long unused, unsigned int esr,
240                                struct pt_regs *regs)
241 {
242         bool handler_found = false;
243 
244         /*
245          * If we are stepping a pending breakpoint, call the hw_breakpoint
246          * handler first.
247          */
248         if (!reinstall_suspended_bps(regs))
249                 return 0;
250 
251         if (!handler_found && call_step_hook(regs, esr) == DBG_HOOK_HANDLED)
252                 handler_found = true;
253 
254         if (!handler_found && user_mode(regs)) {
255                 send_user_sigtrap(TRAP_TRACE);
256 
257                 /*
258                  * ptrace will disable single step unless explicitly
259                  * asked to re-enable it. For other clients, it makes
260                  * sense to leave it enabled (i.e. rewind the controls
261                  * to the active-not-pending state).
262                  */
263                 user_rewind_single_step(current);
264         } else if (!handler_found) {
265                 pr_warn("Unexpected kernel single-step exception at EL1\n");
266                 /*
267                  * Re-enable stepping since we know that we will be
268                  * returning to regs.
269                  */
270                 set_regs_spsr_ss(regs);
271         }
272 
273         return 0;
274 }
275 NOKPROBE_SYMBOL(single_step_handler);
276 
277 static LIST_HEAD(user_break_hook);
278 static LIST_HEAD(kernel_break_hook);
279 
280 void register_user_break_hook(struct break_hook *hook)
281 {
282         register_debug_hook(&hook->node, &user_break_hook);
283 }
284 
285 void unregister_user_break_hook(struct break_hook *hook)
286 {
287         unregister_debug_hook(&hook->node);
288 }
289 
290 void register_kernel_break_hook(struct break_hook *hook)
291 {
292         register_debug_hook(&hook->node, &kernel_break_hook);
293 }
294 
295 void unregister_kernel_break_hook(struct break_hook *hook)
296 {
297         unregister_debug_hook(&hook->node);
298 }
299 
300 static int call_break_hook(struct pt_regs *regs, unsigned int esr)
301 {
302         struct break_hook *hook;
303         struct list_head *list;
304         int (*fn)(struct pt_regs *regs, unsigned int esr) = NULL;
305 
306         list = user_mode(regs) ? &user_break_hook : &kernel_break_hook;
307 
308         /*
309          * Since brk exception disables interrupt, this function is
310          * entirely not preemptible, and we can use rcu list safely here.
311          */
312         list_for_each_entry_rcu(hook, list, node) {
313                 unsigned int comment = esr & ESR_ELx_BRK64_ISS_COMMENT_MASK;
314 
315                 if ((comment & ~hook->mask) == hook->imm)
316                         fn = hook->fn;
317         }
318 
319         return fn ? fn(regs, esr) : DBG_HOOK_ERROR;
320 }
321 NOKPROBE_SYMBOL(call_break_hook);
322 
323 static int brk_handler(unsigned long unused, unsigned int esr,
324                        struct pt_regs *regs)
325 {
326         if (call_break_hook(regs, esr) == DBG_HOOK_HANDLED)
327                 return 0;
328 
329         if (user_mode(regs)) {
330                 send_user_sigtrap(TRAP_BRKPT);
331         } else {
332                 pr_warn("Unexpected kernel BRK exception at EL1\n");
333                 return -EFAULT;
334         }
335 
336         return 0;
337 }
338 NOKPROBE_SYMBOL(brk_handler);
339 
340 int aarch32_break_handler(struct pt_regs *regs)
341 {
342         u32 arm_instr;
343         u16 thumb_instr;
344         bool bp = false;
345         void __user *pc = (void __user *)instruction_pointer(regs);
346 
347         if (!compat_user_mode(regs))
348                 return -EFAULT;
349 
350         if (compat_thumb_mode(regs)) {
351                 /* get 16-bit Thumb instruction */
352                 __le16 instr;
353                 get_user(instr, (__le16 __user *)pc);
354                 thumb_instr = le16_to_cpu(instr);
355                 if (thumb_instr == AARCH32_BREAK_THUMB2_LO) {
356                         /* get second half of 32-bit Thumb-2 instruction */
357                         get_user(instr, (__le16 __user *)(pc + 2));
358                         thumb_instr = le16_to_cpu(instr);
359                         bp = thumb_instr == AARCH32_BREAK_THUMB2_HI;
360                 } else {
361                         bp = thumb_instr == AARCH32_BREAK_THUMB;
362                 }
363         } else {
364                 /* 32-bit ARM instruction */
365                 __le32 instr;
366                 get_user(instr, (__le32 __user *)pc);
367                 arm_instr = le32_to_cpu(instr);
368                 bp = (arm_instr & ~0xf0000000) == AARCH32_BREAK_ARM;
369         }
370 
371         if (!bp)
372                 return -EFAULT;
373 
374         send_user_sigtrap(TRAP_BRKPT);
375         return 0;
376 }
377 NOKPROBE_SYMBOL(aarch32_break_handler);
378 
379 static int __init debug_traps_init(void)
380 {
381         hook_debug_fault_code(DBG_ESR_EVT_HWSS, single_step_handler, SIGTRAP,
382                               TRAP_TRACE, "single-step handler");
383         hook_debug_fault_code(DBG_ESR_EVT_BRK, brk_handler, SIGTRAP,
384                               TRAP_BRKPT, "ptrace BRK handler");
385         return 0;
386 }
387 arch_initcall(debug_traps_init);
388 
389 /* Re-enable single step for syscall restarting. */
390 void 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_ti_thread_flag(task_thread_info(task), TIF_SINGLESTEP))
397                 set_regs_spsr_ss(task_pt_regs(task));
398 }
399 NOKPROBE_SYMBOL(user_rewind_single_step);
400 
401 void user_fastforward_single_step(struct task_struct *task)
402 {
403         if (test_ti_thread_flag(task_thread_info(task), TIF_SINGLESTEP))
404                 clear_regs_spsr_ss(task_pt_regs(task));
405 }
406 
407 /* Kernel API */
408 void kernel_enable_single_step(struct pt_regs *regs)
409 {
410         WARN_ON(!irqs_disabled());
411         set_regs_spsr_ss(regs);
412         mdscr_write(mdscr_read() | DBG_MDSCR_SS);
413         enable_debug_monitors(DBG_ACTIVE_EL1);
414 }
415 NOKPROBE_SYMBOL(kernel_enable_single_step);
416 
417 void kernel_disable_single_step(void)
418 {
419         WARN_ON(!irqs_disabled());
420         mdscr_write(mdscr_read() & ~DBG_MDSCR_SS);
421         disable_debug_monitors(DBG_ACTIVE_EL1);
422 }
423 NOKPROBE_SYMBOL(kernel_disable_single_step);
424 
425 int kernel_active_single_step(void)
426 {
427         WARN_ON(!irqs_disabled());
428         return mdscr_read() & DBG_MDSCR_SS;
429 }
430 NOKPROBE_SYMBOL(kernel_active_single_step);
431 
432 /* ptrace API */
433 void user_enable_single_step(struct task_struct *task)
434 {
435         struct thread_info *ti = task_thread_info(task);
436 
437         if (!test_and_set_ti_thread_flag(ti, TIF_SINGLESTEP))
438                 set_regs_spsr_ss(task_pt_regs(task));
439 }
440 NOKPROBE_SYMBOL(user_enable_single_step);
441 
442 void user_disable_single_step(struct task_struct *task)
443 {
444         clear_ti_thread_flag(task_thread_info(task), TIF_SINGLESTEP);
445 }
446 NOKPROBE_SYMBOL(user_disable_single_step);
447 

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