// SPDX-License-Identifier: GPL-2.0-or-later /* * HW_breakpoint: a unified kernel/user-space hardware breakpoint facility, * using the CPU's debug registers. Derived from * "arch/x86/kernel/hw_breakpoint.c" * * Copyright 2010 IBM Corporation * Author: K.Prasad */ #include #include #include #include #include #include #include #include #include #include #include #include #include #include #include #include #include /* * Stores the breakpoints currently in use on each breakpoint address * register for every cpu */ static DEFINE_PER_CPU(struct perf_event *, bp_per_reg[HBP_NUM_MAX]); /* * Returns total number of data or instruction breakpoints available. */ int hw_breakpoint_slots(int type) { if (type == TYPE_DATA) return nr_wp_slots(); return 0; /* no instruction breakpoints available */ } static bool single_step_pending(void) { int i; for (i = 0; i < nr_wp_slots(); i++) { if (current->thread.last_hit_ubp[i]) return true; } return false; } /* * Install a perf counter breakpoint. * * We seek a free debug address register and use it for this * breakpoint. * * Atomic: we hold the counter->ctx->lock and we only handle variables * and registers local to this cpu. */ int arch_install_hw_breakpoint(struct perf_event *bp) { struct arch_hw_breakpoint *info = counter_arch_bp(bp); struct perf_event **slot; int i; for (i = 0; i < nr_wp_slots(); i++) { slot = this_cpu_ptr(&bp_per_reg[i]); if (!*slot) { *slot = bp; break; } } if (WARN_ONCE(i == nr_wp_slots(), "Can't find any breakpoint slot")) return -EBUSY; /* * Do not install DABR values if the instruction must be single-stepped. * If so, DABR will be populated in single_step_dabr_instruction(). */ if (!single_step_pending()) __set_breakpoint(i, info); return 0; } /* * Uninstall the breakpoint contained in the given counter. * * First we search the debug address register it uses and then we disable * it. * * Atomic: we hold the counter->ctx->lock and we only handle variables * and registers local to this cpu. */ void arch_uninstall_hw_breakpoint(struct perf_event *bp) { struct arch_hw_breakpoint null_brk = {0}; struct perf_event **slot; int i; for (i = 0; i < nr_wp_slots(); i++) { slot = this_cpu_ptr(&bp_per_reg[i]); if (*slot == bp) { *slot = NULL; break; } } if (WARN_ONCE(i == nr_wp_slots(), "Can't find any breakpoint slot")) return; __set_breakpoint(i, &null_brk); } static bool is_ptrace_bp(struct perf_event *bp) { return bp->overflow_handler == ptrace_triggered; } struct breakpoint { struct list_head list; struct perf_event *bp; bool ptrace_bp; }; static DEFINE_PER_CPU(struct breakpoint *, cpu_bps[HBP_NUM_MAX]); static LIST_HEAD(task_bps); static struct breakpoint *alloc_breakpoint(struct perf_event *bp) { struct breakpoint *tmp; tmp = kzalloc(sizeof(*tmp), GFP_KERNEL); if (!tmp) return ERR_PTR(-ENOMEM); tmp->bp = bp; tmp->ptrace_bp = is_ptrace_bp(bp); return tmp; } static bool bp_addr_range_overlap(struct perf_event *bp1, struct perf_event *bp2) { __u64 bp1_saddr, bp1_eaddr, bp2_saddr, bp2_eaddr; bp1_saddr = ALIGN_DOWN(bp1->attr.bp_addr, HW_BREAKPOINT_SIZE); bp1_eaddr = ALIGN(bp1->attr.bp_addr + bp1->attr.bp_len, HW_BREAKPOINT_SIZE); bp2_saddr = ALIGN_DOWN(bp2->attr.bp_addr, HW_BREAKPOINT_SIZE); bp2_eaddr = ALIGN(bp2->attr.bp_addr + bp2->attr.bp_len, HW_BREAKPOINT_SIZE); return (bp1_saddr < bp2_eaddr && bp1_eaddr > bp2_saddr); } static bool alternate_infra_bp(struct breakpoint *b, struct perf_event *bp) { return is_ptrace_bp(bp) ? !b->ptrace_bp : b->ptrace_bp; } static bool can_co_exist(struct breakpoint *b, struct perf_event *bp) { return !(alternate_infra_bp(b, bp) && bp_addr_range_overlap(b->bp, bp)); } static int task_bps_add(struct perf_event *bp) { struct breakpoint *tmp; tmp = alloc_breakpoint(bp); if (IS_ERR(tmp)) return PTR_ERR(tmp); list_add(&tmp->list, &task_bps); return 0; } static void task_bps_remove(struct perf_event *bp) { struct list_head *pos, *q; list_for_each_safe(pos, q, &task_bps) { struct breakpoint *tmp = list_entry(pos, struct breakpoint, list); if (tmp->bp == bp) { list_del(&tmp->list); kfree(tmp); break; } } } /* * If any task has breakpoint from alternate infrastructure, * return true. Otherwise return false. */ static bool all_task_bps_check(struct perf_event *bp) { struct breakpoint *tmp; list_for_each_entry(tmp, &task_bps, list) { if (!can_co_exist(tmp, bp)) return true; } return false; } /* * If same task has breakpoint from alternate infrastructure, * return true. Otherwise return false. */ static bool same_task_bps_check(struct perf_event *bp) { struct breakpoint *tmp; list_for_each_entry(tmp, &task_bps, list) { if (tmp->bp->hw.target == bp->hw.target && !can_co_exist(tmp, bp)) return true; } return false; } static int cpu_bps_add(struct perf_event *bp) { struct breakpoint **cpu_bp; struct breakpoint *tmp; int i = 0; tmp = alloc_breakpoint(bp); if (IS_ERR(tmp)) return PTR_ERR(tmp); cpu_bp = per_cpu_ptr(cpu_bps, bp->cpu); for (i = 0; i < nr_wp_slots(); i++) { if (!cpu_bp[i]) { cpu_bp[i] = tmp; break; } } return 0; } static void cpu_bps_remove(struct perf_event *bp) { struct breakpoint **cpu_bp; int i = 0; cpu_bp = per_cpu_ptr(cpu_bps, bp->cpu); for (i = 0; i < nr_wp_slots(); i++) { if (!cpu_bp[i]) continue; if (cpu_bp[i]->bp == bp) { kfree(cpu_bp[i]); cpu_bp[i] = NULL; break; } } } static bool cpu_bps_check(int cpu, struct perf_event *bp) { struct breakpoint **cpu_bp; int i; cpu_bp = per_cpu_ptr(cpu_bps, cpu); for (i = 0; i < nr_wp_slots(); i++) { if (cpu_bp[i] && !can_co_exist(cpu_bp[i], bp)) return true; } return false; } static bool all_cpu_bps_check(struct perf_event *bp) { int cpu; for_each_online_cpu(cpu) { if (cpu_bps_check(cpu, bp)) return true; } return false; } /* * We don't use any locks to serialize accesses to cpu_bps or task_bps * because are already inside nr_bp_mutex. */ int arch_reserve_bp_slot(struct perf_event *bp) { int ret; /* ptrace breakpoint */ if (is_ptrace_bp(bp)) { if (all_cpu_bps_check(bp)) return -ENOSPC; if (same_task_bps_check(bp)) return -ENOSPC; return task_bps_add(bp); } /* perf breakpoint */ if (is_kernel_addr(bp->attr.bp_addr)) return 0; if (bp->hw.target && bp->cpu == -1) { if (same_task_bps_check(bp)) return -ENOSPC; return task_bps_add(bp); } else if (!bp->hw.target && bp->cpu != -1) { if (all_task_bps_check(bp)) return -ENOSPC; return cpu_bps_add(bp); } if (same_task_bps_check(bp)) return -ENOSPC; ret = cpu_bps_add(bp); if (ret) return ret; ret = task_bps_add(bp); if (ret) cpu_bps_remove(bp); return ret; } void arch_release_bp_slot(struct perf_event *bp) { if (!is_kernel_addr(bp->attr.bp_addr)) { if (bp->hw.target) task_bps_remove(bp); if (bp->cpu != -1) cpu_bps_remove(bp); } } /* * Perform cleanup of arch-specific counters during unregistration * of the perf-event */ void arch_unregister_hw_breakpoint(struct perf_event *bp) { /* * If the breakpoint is unregistered between a hw_breakpoint_handler() * and the single_step_dabr_instruction(), then cleanup the breakpoint * restoration variables to prevent dangling pointers. * FIXME, this should not be using bp->ctx at all! Sayeth peterz. */ if (bp->ctx && bp->ctx->task && bp->ctx->task != ((void *)-1L)) { int i; for (i = 0; i < nr_wp_slots(); i++) { if (bp->ctx->task->thread.last_hit_ubp[i] == bp) bp->ctx->task->thread.last_hit_ubp[i] = NULL; } } } /* * Check for virtual address in kernel space. */ int arch_check_bp_in_kernelspace(struct arch_hw_breakpoint *hw) { return is_kernel_addr(hw->address); } int arch_bp_generic_fields(int type, int *gen_bp_type) { *gen_bp_type = 0; if (type & HW_BRK_TYPE_READ) *gen_bp_type |= HW_BREAKPOINT_R; if (type & HW_BRK_TYPE_WRITE) *gen_bp_type |= HW_BREAKPOINT_W; if (*gen_bp_type == 0) return -EINVAL; return 0; } /* * Watchpoint match range is always doubleword(8 bytes) aligned on * powerpc. If the given range is crossing doubleword boundary, we * need to increase the length such that next doubleword also get * covered. Ex, * * address len = 6 bytes * |=========. * |------------v--|------v--------| * | | | | | | | | | | | | | | | | | * |---------------|---------------| * <---8 bytes---> * * In this case, we should configure hw as: * start_addr = address & ~(HW_BREAKPOINT_SIZE - 1) * len = 16 bytes * * @start_addr is inclusive but @end_addr is exclusive. */ static int hw_breakpoint_validate_len(struct arch_hw_breakpoint *hw) { u16 max_len = DABR_MAX_LEN; u16 hw_len; unsigned long start_addr, end_addr; start_addr = ALIGN_DOWN(hw->address, HW_BREAKPOINT_SIZE); end_addr = ALIGN(hw->address + hw->len, HW_BREAKPOINT_SIZE); hw_len = end_addr - start_addr; if (dawr_enabled()) { max_len = DAWR_MAX_LEN; /* DAWR region can't cross 512 bytes boundary on p10 predecessors */ if (!cpu_has_feature(CPU_FTR_ARCH_31) && (ALIGN_DOWN(start_addr, SZ_512) != ALIGN_DOWN(end_addr - 1, SZ_512))) return -EINVAL; } else if (IS_ENABLED(CONFIG_PPC_8xx)) { /* 8xx can setup a range without limitation */ max_len = U16_MAX; } if (hw_len > max_len) return -EINVAL; hw->hw_len = hw_len; return 0; } /* * Validate the arch-specific HW Breakpoint register settings */ int hw_breakpoint_arch_parse(struct perf_event *bp, const struct perf_event_attr *attr, struct arch_hw_breakpoint *hw) { int ret = -EINVAL; if (!bp || !attr->bp_len) return ret; hw->type = HW_BRK_TYPE_TRANSLATE; if (attr->bp_type & HW_BREAKPOINT_R) hw->type |= HW_BRK_TYPE_READ; if (attr->bp_type & HW_BREAKPOINT_W) hw->type |= HW_BRK_TYPE_WRITE; if (hw->type == HW_BRK_TYPE_TRANSLATE) /* must set alteast read or write */ return ret; if (!attr->exclude_user) hw->type |= HW_BRK_TYPE_USER; if (!attr->exclude_kernel) hw->type |= HW_BRK_TYPE_KERNEL; if (!attr->exclude_hv) hw->type |= HW_BRK_TYPE_HYP; hw->address = attr->bp_addr; hw->len = attr->bp_len; if (!ppc_breakpoint_available()) return -ENODEV; return hw_breakpoint_validate_len(hw); } /* * Restores the breakpoint on the debug registers. * Invoke this function if it is known that the execution context is * about to change to cause loss of MSR_SE settings. */ void thread_change_pc(struct task_struct *tsk, struct pt_regs *regs) { struct arch_hw_breakpoint *info; int i; preempt_disable(); for (i = 0; i < nr_wp_slots(); i++) { if (unlikely(tsk->thread.last_hit_ubp[i])) goto reset; } goto out; reset: regs->msr &= ~MSR_SE; for (i = 0; i < nr_wp_slots(); i++) { info = counter_arch_bp(__this_cpu_read(bp_per_reg[i])); __set_breakpoint(i, info); tsk->thread.last_hit_ubp[i] = NULL; } out: preempt_enable(); } static bool is_larx_stcx_instr(int type) { return type == LARX || type == STCX; } /* * We've failed in reliably handling the hw-breakpoint. Unregister * it and throw a warning message to let the user know about it. */ static void handler_error(struct perf_event *bp, struct arch_hw_breakpoint *info) { WARN(1, "Unable to handle hardware breakpoint. Breakpoint at 0x%lx will be disabled.", info->address); perf_event_disable_inatomic(bp); } static void larx_stcx_err(struct perf_event *bp, struct arch_hw_breakpoint *info) { printk_ratelimited("Breakpoint hit on instruction that can't be emulated. Breakpoint at 0x%lx will be disabled.\n", info->address); perf_event_disable_inatomic(bp); } static bool stepping_handler(struct pt_regs *regs, struct perf_event **bp, struct arch_hw_breakpoint **info, int *hit, struct ppc_inst instr) { int i; int stepped; /* Do not emulate user-space instructions, instead single-step them */ if (user_mode(regs)) { for (i = 0; i < nr_wp_slots(); i++) { if (!hit[i]) continue; current->thread.last_hit_ubp[i] = bp[i]; info[i] = NULL; } regs->msr |= MSR_SE; return false; } stepped = emulate_step(regs, instr); if (!stepped) { for (i = 0; i < nr_wp_slots(); i++) { if (!hit[i]) continue; handler_error(bp[i], info[i]); info[i] = NULL; } return false; } return true; } int hw_breakpoint_handler(struct die_args *args) { bool err = false; int rc = NOTIFY_STOP; struct perf_event *bp[HBP_NUM_MAX] = { NULL }; struct pt_regs *regs = args->regs; struct arch_hw_breakpoint *info[HBP_NUM_MAX] = { NULL }; int i; int hit[HBP_NUM_MAX] = {0}; int nr_hit = 0; bool ptrace_bp = false; struct ppc_inst instr = ppc_inst(0); int type = 0; int size = 0; unsigned long ea; /* Disable breakpoints during exception handling */ hw_breakpoint_disable(); /* * The counter may be concurrently released but that can only * occur from a call_rcu() path. We can then safely fetch * the breakpoint, use its callback, touch its counter * while we are in an rcu_read_lock() path. */ rcu_read_lock(); if (!IS_ENABLED(CONFIG_PPC_8xx)) wp_get_instr_detail(regs, &instr, &type, &size, &ea); for (i = 0; i < nr_wp_slots(); i++) { bp[i] = __this_cpu_read(bp_per_reg[i]); if (!bp[i]) continue; info[i] = counter_arch_bp(bp[i]); info[i]->type &= ~HW_BRK_TYPE_EXTRANEOUS_IRQ; if (wp_check_constraints(regs, instr, ea, type, size, info[i])) { if (!IS_ENABLED(CONFIG_PPC_8xx) && ppc_inst_equal(instr, ppc_inst(0))) { handler_error(bp[i], info[i]); info[i] = NULL; err = 1; continue; } if (is_ptrace_bp(bp[i])) ptrace_bp = true; hit[i] = 1; nr_hit++; } } if (err) goto reset; if (!nr_hit) { rc = NOTIFY_DONE; goto out; } /* * Return early after invoking user-callback function without restoring * DABR if the breakpoint is from ptrace which always operates in * one-shot mode. The ptrace-ed process will receive the SIGTRAP signal * generated in do_dabr(). */ if (ptrace_bp) { for (i = 0; i < nr_wp_slots(); i++) { if (!hit[i]) continue; perf_bp_event(bp[i], regs); info[i] = NULL; } rc = NOTIFY_DONE; goto reset; } if (!IS_ENABLED(CONFIG_PPC_8xx)) { if (is_larx_stcx_instr(type)) { for (i = 0; i < nr_wp_slots(); i++) { if (!hit[i]) continue; larx_stcx_err(bp[i], info[i]); info[i] = NULL; } goto reset; } if (!stepping_handler(regs, bp, info, hit, instr)) goto reset; } /* * As a policy, the callback is invoked in a 'trigger-after-execute' * fashion */ for (i = 0; i < nr_wp_slots(); i++) { if (!hit[i]) continue; if (!(info[i]->type & HW_BRK_TYPE_EXTRANEOUS_IRQ)) perf_bp_event(bp[i], regs); } reset: for (i = 0; i < nr_wp_slots(); i++) { if (!info[i]) continue; __set_breakpoint(i, info[i]); } out: rcu_read_unlock(); return rc; } NOKPROBE_SYMBOL(hw_breakpoint_handler); /* * Handle single-step exceptions following a DABR hit. */ static int single_step_dabr_instruction(struct die_args *args) { struct pt_regs *regs = args->regs; struct perf_event *bp = NULL; struct arch_hw_breakpoint *info; int i; bool found = false; /* * Check if we are single-stepping as a result of a * previous HW Breakpoint exception */ for (i = 0; i < nr_wp_slots(); i++) { bp = current->thread.last_hit_ubp[i]; if (!bp) continue; found = true; info = counter_arch_bp(bp); /* * We shall invoke the user-defined callback function in the * single stepping handler to confirm to 'trigger-after-execute' * semantics */ if (!(info->type & HW_BRK_TYPE_EXTRANEOUS_IRQ)) perf_bp_event(bp, regs); current->thread.last_hit_ubp[i] = NULL; } if (!found) return NOTIFY_DONE; for (i = 0; i < nr_wp_slots(); i++) { bp = __this_cpu_read(bp_per_reg[i]); if (!bp) continue; info = counter_arch_bp(bp); __set_breakpoint(i, info); } /* * If the process was being single-stepped by ptrace, let the * other single-step actions occur (e.g. generate SIGTRAP). */ if (test_thread_flag(TIF_SINGLESTEP)) return NOTIFY_DONE; return NOTIFY_STOP; } NOKPROBE_SYMBOL(single_step_dabr_instruction); /* * Handle debug exception notifications. */ int hw_breakpoint_exceptions_notify( struct notifier_block *unused, unsigned long val, void *data) { int ret = NOTIFY_DONE; switch (val) { case DIE_DABR_MATCH: ret = hw_breakpoint_handler(data); break; case DIE_SSTEP: ret = single_step_dabr_instruction(data); break; } return ret; } NOKPROBE_SYMBOL(hw_breakpoint_exceptions_notify); /* * Release the user breakpoints used by ptrace */ void flush_ptrace_hw_breakpoint(struct task_struct *tsk) { int i; struct thread_struct *t = &tsk->thread; for (i = 0; i < nr_wp_slots(); i++) { unregister_hw_breakpoint(t->ptrace_bps[i]); t->ptrace_bps[i] = NULL; } } void hw_breakpoint_pmu_read(struct perf_event *bp) { /* TODO */ } void ptrace_triggered(struct perf_event *bp, struct perf_sample_data *data, struct pt_regs *regs) { struct perf_event_attr attr; /* * Disable the breakpoint request here since ptrace has defined a * one-shot behaviour for breakpoint exceptions in PPC64. * The SIGTRAP signal is generated automatically for us in do_dabr(). * We don't have to do anything about that here */ attr = bp->attr; attr.disabled = true; modify_user_hw_breakpoint(bp, &attr); }