/*
* HW_breakpoint: a unified kernel/user-space hardware breakpoint facility,
* using the CPU's debug registers. Derived from
* "arch/x86/kernel/hw_breakpoint.c"
*
* This program is free software; you can redistribute it and/or modify
* it under the terms of the GNU General Public License as published by
* the Free Software Foundation; either version 2 of the License, or
* (at your option) any later version.
*
* This program is distributed in the hope that it will be useful,
* but WITHOUT ANY WARRANTY; without even the implied warranty of
* MERCHANTABILITY or FITNESS FOR A PARTICULAR PURPOSE. See the
* GNU General Public License for more details.
*
* You should have received a copy of the GNU General Public License
* along with this program; if not, write to the Free Software
* Foundation, Inc., 59 Temple Place - Suite 330, Boston, MA 02111-1307, USA.
*
* Copyright 2010 IBM Corporation
* Author: K.Prasad <prasad@linux.vnet.ibm.com>
*
*/
#include <linux/hw_breakpoint.h>
#include <linux/notifier.h>
#include <linux/kprobes.h>
#include <linux/percpu.h>
#include <linux/kernel.h>
#include <linux/module.h>
#include <linux/sched.h>
#include <linux/init.h>
#include <linux/smp.h>
#include <asm/hw_breakpoint.h>
#include <asm/processor.h>
#include <asm/sstep.h>
#include <asm/uaccess.h>
/*
* 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 = &__get_cpu_var(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_dabr(info->address | info->type | DABR_TRANSLATION);
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 = &__get_cpu_var(bp_per_reg);
if (*slot != bp) {
WARN_ONCE(1, "Can't find the breakpoint");
return;
}
*slot = NULL;
set_dabr(0);
}
/*
* 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.
*/
if (bp->ctx->task)
bp->ctx->task->thread.last_hit_ubp = NULL;
}
/*
* Check for virtual address in kernel space.
*/
int arch_check_bp_in_kernelspace(struct perf_event *bp)
{
struct arch_hw_breakpoint *info = counter_arch_bp(bp);
return is_kernel_addr(info->address);
}
int arch_bp_generic_fields(int type, int *gen_bp_type)
{
switch (type) {
case DABR_DATA_READ:
*gen_bp_type = HW_BREAKPOINT_R;
break;
case DABR_DATA_WRITE:
*gen_bp_type = HW_BREAKPOINT_W;
break;
case (DABR_DATA_WRITE | DABR_DATA_READ):
*gen_bp_type = (HW_BREAKPOINT_W | HW_BREAKPOINT_R);
break;
default:
return -EINVAL;
}
return 0;
}
/*
* Validate the arch-specific HW Breakpoint register settings
*/
int arch_validate_hwbkpt_settings(struct perf_event *bp)
{
int ret = -EINVAL;
struct arch_hw_breakpoint *info = counter_arch_bp(bp);
if (!bp)
return ret;
switch (bp->attr.bp_type) {
case HW_BREAKPOINT_R:
info->type = DABR_DATA_READ;
break;
case HW_BREAKPOINT_W:
info->type = DABR_DATA_WRITE;
break;
case HW_BREAKPOINT_R | HW_BREAKPOINT_W:
info->type = (DABR_DATA_READ | DABR_DATA_WRITE);
break;
default:
return ret;
}
info->address = bp->attr.bp_addr;
info->len = bp->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 (info->len >
(HW_BREAKPOINT_LEN - (info->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_dabr(info->address | info->type | DABR_TRANSLATION);
tsk->thread.last_hit_ubp = NULL;
}
/*
* Handle debug exception notifications.
*/
int __kprobes hw_breakpoint_handler(struct die_args *args)
{
int rc = NOTIFY_STOP;
struct perf_event *bp;
struct pt_regs *regs = args->regs;
int stepped = 1;
struct arch_hw_breakpoint *info;
unsigned int instr;
unsigned long dar = regs->dar;
/* Disable breakpoints during exception handling */
set_dabr(0);
/*
* 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 = __get_cpu_var(bp_per_reg);
if (!bp)
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->extraneous_interrupt = !((bp->attr.bp_addr <= dar) &&
(dar - bp->attr.bp_addr < bp->attr.bp_len));
/* Do not emulate user-space instructions, instead single-step them */
if (user_mode(regs)) {
bp->ctx->task->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(bp);
goto out;
}
/*
* As a policy, the callback is invoked in a 'trigger-after-execute'
* fashion
*/
if (!info->extraneous_interrupt)
perf_bp_event(bp, regs);
set_dabr(info->address | info->type | DABR_TRANSLATION);
out:
rcu_read_unlock();
return rc;
}
/*
* Handle single-step exceptions following a DABR hit.
*/
int __kprobes single_step_dabr_instruction(struct die_args *args)
{
struct pt_regs *regs = args->regs;
struct perf_event *bp = NULL;
struct arch_hw_breakpoint *bp_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;
bp_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 (!bp_info->extraneous_interrupt)
perf_bp_event(bp, regs);
set_dabr(bp_info->address | bp_info->type | DABR_TRANSLATION);
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;
}
/*
* Handle debug exception notifications.
*/
int __kprobes 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;
}
/*
* 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 */
}
