1 // SPDX-License-Identifier: GPL-2.0-or-later
4 * Copyright (C) 2007 Alan Stern
5 * Copyright (C) 2009 IBM Corporation
6 * Copyright (C) 2009 Frederic Weisbecker <fweisbec@gmail.com>
8 * Authors: Alan Stern <stern@rowland.harvard.edu>
9 * K.Prasad <prasad@linux.vnet.ibm.com>
10 * Frederic Weisbecker <fweisbec@gmail.com>
14 * HW_breakpoint: a unified kernel/user-space hardware breakpoint facility,
15 * using the CPU's debug registers.
18 #include <linux/perf_event.h>
19 #include <linux/hw_breakpoint.h>
20 #include <linux/irqflags.h>
21 #include <linux/notifier.h>
22 #include <linux/kallsyms.h>
23 #include <linux/kprobes.h>
24 #include <linux/percpu.h>
25 #include <linux/kdebug.h>
26 #include <linux/kernel.h>
27 #include <linux/export.h>
28 #include <linux/sched.h>
29 #include <linux/smp.h>
31 #include <asm/hw_breakpoint.h>
32 #include <asm/processor.h>
33 #include <asm/debugreg.h>
36 #include <asm/tlbflush.h>
38 /* Per cpu debug control register value */
39 DEFINE_PER_CPU(unsigned long, cpu_dr7);
40 EXPORT_PER_CPU_SYMBOL(cpu_dr7);
42 /* Per cpu debug address registers values */
43 static DEFINE_PER_CPU(unsigned long, cpu_debugreg[HBP_NUM]);
46 * Stores the breakpoints currently in use on each breakpoint address
47 * register for each cpus
49 static DEFINE_PER_CPU(struct perf_event *, bp_per_reg[HBP_NUM]);
52 static inline unsigned long
53 __encode_dr7(int drnum, unsigned int len, unsigned int type)
55 unsigned long bp_info;
57 bp_info = (len | type) & 0xf;
58 bp_info <<= (DR_CONTROL_SHIFT + drnum * DR_CONTROL_SIZE);
59 bp_info |= (DR_GLOBAL_ENABLE << (drnum * DR_ENABLE_SIZE));
65 * Encode the length, type, Exact, and Enable bits for a particular breakpoint
66 * as stored in debug register 7.
68 unsigned long encode_dr7(int drnum, unsigned int len, unsigned int type)
70 return __encode_dr7(drnum, len, type) | DR_GLOBAL_SLOWDOWN;
74 * Decode the length and type bits for a particular breakpoint as
75 * stored in debug register 7. Return the "enabled" status.
77 int decode_dr7(unsigned long dr7, int bpnum, unsigned *len, unsigned *type)
79 int bp_info = dr7 >> (DR_CONTROL_SHIFT + bpnum * DR_CONTROL_SIZE);
81 *len = (bp_info & 0xc) | 0x40;
82 *type = (bp_info & 0x3) | 0x80;
84 return (dr7 >> (bpnum * DR_ENABLE_SIZE)) & 0x3;
88 * Install a perf counter breakpoint.
90 * We seek a free debug address register and use it for this
91 * breakpoint. Eventually we enable it in the debug control register.
93 * Atomic: we hold the counter->ctx->lock and we only handle variables
94 * and registers local to this cpu.
96 int arch_install_hw_breakpoint(struct perf_event *bp)
98 struct arch_hw_breakpoint *info = counter_arch_bp(bp);
102 lockdep_assert_irqs_disabled();
104 for (i = 0; i < HBP_NUM; i++) {
105 struct perf_event **slot = this_cpu_ptr(&bp_per_reg[i]);
113 if (WARN_ONCE(i == HBP_NUM, "Can't find any breakpoint slot"))
116 set_debugreg(info->address, i);
117 __this_cpu_write(cpu_debugreg[i], info->address);
119 dr7 = this_cpu_ptr(&cpu_dr7);
120 *dr7 |= encode_dr7(i, info->len, info->type);
123 * Ensure we first write cpu_dr7 before we set the DR7 register.
124 * This ensures an NMI never see cpu_dr7 0 when DR7 is not.
128 set_debugreg(*dr7, 7);
130 set_dr_addr_mask(info->mask, i);
136 * Uninstall the breakpoint contained in the given counter.
138 * First we search the debug address register it uses and then we disable
141 * Atomic: we hold the counter->ctx->lock and we only handle variables
142 * and registers local to this cpu.
144 void arch_uninstall_hw_breakpoint(struct perf_event *bp)
146 struct arch_hw_breakpoint *info = counter_arch_bp(bp);
150 lockdep_assert_irqs_disabled();
152 for (i = 0; i < HBP_NUM; i++) {
153 struct perf_event **slot = this_cpu_ptr(&bp_per_reg[i]);
161 if (WARN_ONCE(i == HBP_NUM, "Can't find any breakpoint slot"))
164 dr7 = this_cpu_read(cpu_dr7);
165 dr7 &= ~__encode_dr7(i, info->len, info->type);
167 set_debugreg(dr7, 7);
169 set_dr_addr_mask(0, i);
172 * Ensure the write to cpu_dr7 is after we've set the DR7 register.
173 * This ensures an NMI never see cpu_dr7 0 when DR7 is not.
177 this_cpu_write(cpu_dr7, dr7);
180 static int arch_bp_generic_len(int x86_len)
183 case X86_BREAKPOINT_LEN_1:
184 return HW_BREAKPOINT_LEN_1;
185 case X86_BREAKPOINT_LEN_2:
186 return HW_BREAKPOINT_LEN_2;
187 case X86_BREAKPOINT_LEN_4:
188 return HW_BREAKPOINT_LEN_4;
190 case X86_BREAKPOINT_LEN_8:
191 return HW_BREAKPOINT_LEN_8;
198 int arch_bp_generic_fields(int x86_len, int x86_type,
199 int *gen_len, int *gen_type)
205 case X86_BREAKPOINT_EXECUTE:
206 if (x86_len != X86_BREAKPOINT_LEN_X)
209 *gen_type = HW_BREAKPOINT_X;
210 *gen_len = sizeof(long);
212 case X86_BREAKPOINT_WRITE:
213 *gen_type = HW_BREAKPOINT_W;
215 case X86_BREAKPOINT_RW:
216 *gen_type = HW_BREAKPOINT_W | HW_BREAKPOINT_R;
223 len = arch_bp_generic_len(x86_len);
232 * Check for virtual address in kernel space.
234 int arch_check_bp_in_kernelspace(struct arch_hw_breakpoint *hw)
240 len = arch_bp_generic_len(hw->len);
241 WARN_ON_ONCE(len < 0);
244 * We don't need to worry about va + len - 1 overflowing:
245 * we already require that va is aligned to a multiple of len.
247 return (va >= TASK_SIZE_MAX) || ((va + len - 1) >= TASK_SIZE_MAX);
251 * Checks whether the range [addr, end], overlaps the area [base, base + size).
253 static inline bool within_area(unsigned long addr, unsigned long end,
254 unsigned long base, unsigned long size)
256 return end >= base && addr < (base + size);
260 * Checks whether the range from addr to end, inclusive, overlaps the fixed
261 * mapped CPU entry area range or other ranges used for CPU entry.
263 static inline bool within_cpu_entry(unsigned long addr, unsigned long end)
267 /* CPU entry erea is always used for CPU entry */
268 if (within_area(addr, end, CPU_ENTRY_AREA_BASE,
269 CPU_ENTRY_AREA_TOTAL_SIZE))
272 for_each_possible_cpu(cpu) {
273 /* The original rw GDT is being used after load_direct_gdt() */
274 if (within_area(addr, end, (unsigned long)get_cpu_gdt_rw(cpu),
279 * cpu_tss_rw is not directly referenced by hardware, but
280 * cpu_tss_rw is also used in CPU entry code,
282 if (within_area(addr, end,
283 (unsigned long)&per_cpu(cpu_tss_rw, cpu),
284 sizeof(struct tss_struct)))
288 * cpu_tlbstate.user_pcid_flush_mask is used for CPU entry.
289 * If a data breakpoint on it, it will cause an unwanted #DB.
290 * Protect the full cpu_tlbstate structure to be sure.
292 if (within_area(addr, end,
293 (unsigned long)&per_cpu(cpu_tlbstate, cpu),
294 sizeof(struct tlb_state)))
301 static int arch_build_bp_info(struct perf_event *bp,
302 const struct perf_event_attr *attr,
303 struct arch_hw_breakpoint *hw)
305 unsigned long bp_end;
307 bp_end = attr->bp_addr + attr->bp_len - 1;
308 if (bp_end < attr->bp_addr)
312 * Prevent any breakpoint of any type that overlaps the CPU
313 * entry area and data. This protects the IST stacks and also
314 * reduces the chance that we ever find out what happens if
315 * there's a data breakpoint on the GDT, IDT, or TSS.
317 if (within_cpu_entry(attr->bp_addr, bp_end))
320 hw->address = attr->bp_addr;
324 switch (attr->bp_type) {
325 case HW_BREAKPOINT_W:
326 hw->type = X86_BREAKPOINT_WRITE;
328 case HW_BREAKPOINT_W | HW_BREAKPOINT_R:
329 hw->type = X86_BREAKPOINT_RW;
331 case HW_BREAKPOINT_X:
333 * We don't allow kernel breakpoints in places that are not
334 * acceptable for kprobes. On non-kprobes kernels, we don't
335 * allow kernel breakpoints at all.
337 if (attr->bp_addr >= TASK_SIZE_MAX) {
338 if (within_kprobe_blacklist(attr->bp_addr))
342 hw->type = X86_BREAKPOINT_EXECUTE;
344 * x86 inst breakpoints need to have a specific undefined len.
345 * But we still need to check userspace is not trying to setup
346 * an unsupported length, to get a range breakpoint for example.
348 if (attr->bp_len == sizeof(long)) {
349 hw->len = X86_BREAKPOINT_LEN_X;
358 switch (attr->bp_len) {
359 case HW_BREAKPOINT_LEN_1:
360 hw->len = X86_BREAKPOINT_LEN_1;
362 case HW_BREAKPOINT_LEN_2:
363 hw->len = X86_BREAKPOINT_LEN_2;
365 case HW_BREAKPOINT_LEN_4:
366 hw->len = X86_BREAKPOINT_LEN_4;
369 case HW_BREAKPOINT_LEN_8:
370 hw->len = X86_BREAKPOINT_LEN_8;
374 /* AMD range breakpoint */
375 if (!is_power_of_2(attr->bp_len))
377 if (attr->bp_addr & (attr->bp_len - 1))
380 if (!boot_cpu_has(X86_FEATURE_BPEXT))
384 * It's impossible to use a range breakpoint to fake out
385 * user vs kernel detection because bp_len - 1 can't
386 * have the high bit set. If we ever allow range instruction
387 * breakpoints, then we'll have to check for kprobe-blacklisted
388 * addresses anywhere in the range.
390 hw->mask = attr->bp_len - 1;
391 hw->len = X86_BREAKPOINT_LEN_1;
398 * Validate the arch-specific HW Breakpoint register settings
400 int hw_breakpoint_arch_parse(struct perf_event *bp,
401 const struct perf_event_attr *attr,
402 struct arch_hw_breakpoint *hw)
408 ret = arch_build_bp_info(bp, attr, hw);
413 case X86_BREAKPOINT_LEN_1:
418 case X86_BREAKPOINT_LEN_2:
421 case X86_BREAKPOINT_LEN_4:
425 case X86_BREAKPOINT_LEN_8:
435 * Check that the low-order bits of the address are appropriate
436 * for the alignment implied by len.
438 if (hw->address & align)
445 * Release the user breakpoints used by ptrace
447 void flush_ptrace_hw_breakpoint(struct task_struct *tsk)
450 struct thread_struct *t = &tsk->thread;
452 for (i = 0; i < HBP_NUM; i++) {
453 unregister_hw_breakpoint(t->ptrace_bps[i]);
454 t->ptrace_bps[i] = NULL;
461 void hw_breakpoint_restore(void)
463 set_debugreg(__this_cpu_read(cpu_debugreg[0]), 0);
464 set_debugreg(__this_cpu_read(cpu_debugreg[1]), 1);
465 set_debugreg(__this_cpu_read(cpu_debugreg[2]), 2);
466 set_debugreg(__this_cpu_read(cpu_debugreg[3]), 3);
467 set_debugreg(DR6_RESERVED, 6);
468 set_debugreg(__this_cpu_read(cpu_dr7), 7);
470 EXPORT_SYMBOL_GPL(hw_breakpoint_restore);
473 * Handle debug exception notifications.
475 * Return value is either NOTIFY_STOP or NOTIFY_DONE as explained below.
477 * NOTIFY_DONE returned if one of the following conditions is true.
478 * i) When the causative address is from user-space and the exception
479 * is a valid one, i.e. not triggered as a result of lazy debug register
481 * ii) When there are more bits than trap<n> set in DR6 register (such
482 * as BD, BS or BT) indicating that more than one debug condition is
483 * met and requires some more action in do_debug().
485 * NOTIFY_STOP returned for all other cases
488 static int hw_breakpoint_handler(struct die_args *args)
490 int i, rc = NOTIFY_STOP;
491 struct perf_event *bp;
492 unsigned long *dr6_p;
495 /* The DR6 value is pointed by args->err */
496 dr6_p = (unsigned long *)ERR_PTR(args->err);
499 /* If it's a single step, TRAP bits are random */
503 /* Do an early return if no trap bits are set in DR6 */
504 if ((dr6 & DR_TRAP_BITS) == 0)
507 /* Handle all the breakpoints that were triggered */
508 for (i = 0; i < HBP_NUM; ++i) {
509 if (likely(!(dr6 & (DR_TRAP0 << i))))
513 * The counter may be concurrently released but that can only
514 * occur from a call_rcu() path. We can then safely fetch
515 * the breakpoint, use its callback, touch its counter
516 * while we are in an rcu_read_lock() path.
520 bp = this_cpu_read(bp_per_reg[i]);
522 * Reset the 'i'th TRAP bit in dr6 to denote completion of
525 (*dr6_p) &= ~(DR_TRAP0 << i);
527 * bp can be NULL due to lazy debug register switching
528 * or due to concurrent perf counter removing.
535 perf_bp_event(bp, args->regs);
538 * Set up resume flag to avoid breakpoint recursion when
539 * returning back to origin.
541 if (bp->hw.info.type == X86_BREAKPOINT_EXECUTE)
542 args->regs->flags |= X86_EFLAGS_RF;
547 * Further processing in do_debug() is needed for a) user-space
548 * breakpoints (to generate signals) and b) when the system has
549 * taken exception due to multiple causes
551 if ((current->thread.virtual_dr6 & DR_TRAP_BITS) ||
552 (dr6 & (~DR_TRAP_BITS)))
559 * Handle debug exception notifications.
561 int hw_breakpoint_exceptions_notify(
562 struct notifier_block *unused, unsigned long val, void *data)
564 if (val != DIE_DEBUG)
567 return hw_breakpoint_handler(data);
570 void hw_breakpoint_pmu_read(struct perf_event *bp)