blob: f4e8f21046f547a5437acf7ed1a41d108f48aa32 [file] [log] [blame]
// 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 <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/sched.h>
#include <linux/smp.h>
#include <linux/debugfs.h>
#include <linux/init.h>
#include <asm/hw_breakpoint.h>
#include <asm/processor.h>
#include <asm/sstep.h>
#include <asm/debug.h>
#include <asm/debugfs.h>
#include <asm/hvcall.h>
#include <asm/inst.h>
#include <linux/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[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;
for (i = 0; i < nr_wp_slots(); i++) {
if (unlikely(tsk->thread.last_hit_ubp[i]))
goto reset;
}
return;
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;
}
}
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);
}