// 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 /* * Stores the breakpoints currently in use on each breakpoint address * register for every cpu */ static DEFINE_PER_CPU(struct perf_event *, bp_per_reg); /* * Returns total number of data or instruction breakpoints available. */ int hw_breakpoint_slots(int type) { if (type == TYPE_DATA) return HBP_NUM; return 0; /* no instruction breakpoints available */ } /* * 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 = this_cpu_ptr(&bp_per_reg); *slot = bp; /* * Do not install DABR values if the instruction must be single-stepped. * If so, DABR will be populated in single_step_dabr_instruction(). */ if (current->thread.last_hit_ubp != bp) __set_breakpoint(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 perf_event **slot = this_cpu_ptr(&bp_per_reg); if (*slot != bp) { WARN_ONCE(1, "Can't find the breakpoint"); return; } *slot = NULL; hw_breakpoint_disable(); } /* * 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)) bp->ctx->task->thread.last_hit_ubp = 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; } /* * 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, length_max; if (!bp) 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; /* * Since breakpoint length can be a maximum of HW_BREAKPOINT_LEN(8) * and breakpoint addresses are aligned to nearest double-word * HW_BREAKPOINT_ALIGN by rounding off to the lower address, the * 'symbolsize' should satisfy the check below. */ if (!ppc_breakpoint_available()) return -ENODEV; length_max = 8; /* DABR */ if (dawr_enabled()) { length_max = 512 ; /* 64 doublewords */ /* DAWR region can't cross 512 boundary */ if ((attr->bp_addr >> 9) != ((attr->bp_addr + attr->bp_len - 1) >> 9)) return -EINVAL; } if (hw->len > (length_max - (hw->address & HW_BREAKPOINT_ALIGN))) return -EINVAL; return 0; } /* * 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; if (likely(!tsk->thread.last_hit_ubp)) return; info = counter_arch_bp(tsk->thread.last_hit_ubp); regs->msr &= ~MSR_SE; __set_breakpoint(info); tsk->thread.last_hit_ubp = NULL; } /* * Handle debug exception notifications. */ int hw_breakpoint_handler(struct die_args *args) { int rc = NOTIFY_STOP; struct perf_event *bp; struct pt_regs *regs = args->regs; #ifndef CONFIG_PPC_8xx int stepped = 1; unsigned int instr; #endif struct arch_hw_breakpoint *info; unsigned long dar = regs->dar; /* 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(); bp = __this_cpu_read(bp_per_reg); if (!bp) { rc = NOTIFY_DONE; goto out; } info = counter_arch_bp(bp); /* * 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 (bp->overflow_handler == ptrace_triggered) { perf_bp_event(bp, regs); rc = NOTIFY_DONE; goto out; } /* * Verify if dar lies within the address range occupied by the symbol * being watched to filter extraneous exceptions. If it doesn't, * we still need to single-step the instruction, but we don't * generate an event. */ info->type &= ~HW_BRK_TYPE_EXTRANEOUS_IRQ; if (!((bp->attr.bp_addr <= dar) && (dar - bp->attr.bp_addr < bp->attr.bp_len))) info->type |= HW_BRK_TYPE_EXTRANEOUS_IRQ; #ifndef CONFIG_PPC_8xx /* Do not emulate user-space instructions, instead single-step them */ if (user_mode(regs)) { current->thread.last_hit_ubp = bp; regs->msr |= MSR_SE; goto out; } stepped = 0; instr = 0; if (!__get_user_inatomic(instr, (unsigned int *) regs->nip)) stepped = emulate_step(regs, instr); /* * emulate_step() could not execute it. We've failed in reliably * handling the hw-breakpoint. Unregister it and throw a warning * message to let the user know about it. */ if (!stepped) { WARN(1, "Unable to handle hardware breakpoint. Breakpoint at " "0x%lx will be disabled.", info->address); perf_event_disable_inatomic(bp); goto out; } #endif /* * As a policy, the callback is invoked in a 'trigger-after-execute' * fashion */ if (!(info->type & HW_BRK_TYPE_EXTRANEOUS_IRQ)) perf_bp_event(bp, regs); __set_breakpoint(info); 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; bp = current->thread.last_hit_ubp; /* * Check if we are single-stepping as a result of a * previous HW Breakpoint exception */ if (!bp) return NOTIFY_DONE; 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); __set_breakpoint(info); current->thread.last_hit_ubp = NULL; /* * 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) { struct thread_struct *t = &tsk->thread; unregister_hw_breakpoint(t->ptrace_bps[0]); t->ptrace_bps[0] = NULL; } void hw_breakpoint_pmu_read(struct perf_event *bp) { /* TODO */ } bool dawr_force_enable; EXPORT_SYMBOL_GPL(dawr_force_enable); static ssize_t dawr_write_file_bool(struct file *file, const char __user *user_buf, size_t count, loff_t *ppos) { struct arch_hw_breakpoint null_brk = {0, 0, 0}; size_t rc; /* Send error to user if they hypervisor won't allow us to write DAWR */ if ((!dawr_force_enable) && (firmware_has_feature(FW_FEATURE_LPAR)) && (set_dawr(&null_brk) != H_SUCCESS)) return -1; rc = debugfs_write_file_bool(file, user_buf, count, ppos); if (rc) return rc; /* If we are clearing, make sure all CPUs have the DAWR cleared */ if (!dawr_force_enable) smp_call_function((smp_call_func_t)set_dawr, &null_brk, 0); return rc; } static const struct file_operations dawr_enable_fops = { .read = debugfs_read_file_bool, .write = dawr_write_file_bool, .open = simple_open, .llseek = default_llseek, }; static int __init dawr_force_setup(void) { dawr_force_enable = false; if (cpu_has_feature(CPU_FTR_DAWR)) { /* Don't setup sysfs file for user control on P8 */ dawr_force_enable = true; return 0; } if (PVR_VER(mfspr(SPRN_PVR)) == PVR_POWER9) { /* Turn DAWR off by default, but allow admin to turn it on */ dawr_force_enable = false; debugfs_create_file_unsafe("dawr_enable_dangerous", 0600, powerpc_debugfs_root, &dawr_force_enable, &dawr_enable_fops); } return 0; } arch_initcall(dawr_force_setup);