On ARM platforms is_default_overflow_handler() is used to determine if
hw_breakpoint code should single-step over the watchpoint trigger or
let the custom handler deal with it.
Attaching a BPF program to a watchpoint replaces the handler with
bpf_overflow_handler, which isn't recognized as a default handler so we
never step over the instruction triggering the data abort exception (the
watchpoint keeps firing):
# bpftrace -e 'watchpoint:0x10000000:4:w { printf("hit\n"); }' ./wp_test
Attaching 1 probe...
hit
hit
hit
[...]
(wp_test performs a single 4-byte store to address 0x10000000)
This patch replaces the check with uses_default_overflow_handler(), which
accounts for the bpf_overflow_handler() case by also testing if the handler
invokes one of the perf_event_output functions via orig_default_handler.
Signed-off-by: Tomislav Novak <tnovak@xxxxxx>
Tested-by: Samuel Gosselin <sgosselin@xxxxxx> # arm64
---
arch/arm/kernel/hw_breakpoint.c | 8 ++++----
arch/arm64/kernel/hw_breakpoint.c | 4 ++--
include/linux/perf_event.h | 22 +++++++++++++++++++---
3 files changed, 25 insertions(+), 9 deletions(-)
diff --git a/arch/arm/kernel/hw_breakpoint.c b/arch/arm/kernel/hw_breakpoint.c
index 054e9199f30d..dc0fb7a81371 100644
--- a/arch/arm/kernel/hw_breakpoint.c
+++ b/arch/arm/kernel/hw_breakpoint.c
@@ -626,7 +626,7 @@ int hw_breakpoint_arch_parse(struct perf_event *bp,
hw->address &= ~alignment_mask;
hw->ctrl.len <<= offset;
- if (is_default_overflow_handler(bp)) {
+ if (uses_default_overflow_handler(bp)) {
/*
* Mismatch breakpoints are required for single-stepping
* breakpoints.
@@ -798,7 +798,7 @@ static void watchpoint_handler(unsigned long addr, unsigned int fsr,
* Otherwise, insert a temporary mismatch breakpoint so that
* we can single-step over the watchpoint trigger.
*/
- if (!is_default_overflow_handler(wp))
+ if (!uses_default_overflow_handler(wp))
continue;
step:
enable_single_step(wp, instruction_pointer(regs));
@@ -811,7 +811,7 @@ static void watchpoint_handler(unsigned long addr, unsigned int fsr,
info->trigger = addr;
pr_debug("watchpoint fired: address = 0x%x\n", info->trigger);
perf_bp_event(wp, regs);
- if (is_default_overflow_handler(wp))
+ if (uses_default_overflow_handler(wp))
enable_single_step(wp, instruction_pointer(regs));
}
@@ -886,7 +886,7 @@ static void breakpoint_handler(unsigned long unknown, struct pt_regs *regs)
info->trigger = addr;
pr_debug("breakpoint fired: address = 0x%x\n", addr);
perf_bp_event(bp, regs);
- if (is_default_overflow_handler(bp))
+ if (uses_default_overflow_handler(bp))
enable_single_step(bp, addr);
goto unlock;
}
diff --git a/arch/arm64/kernel/hw_breakpoint.c b/arch/arm64/kernel/hw_breakpoint.c
index b29a311bb055..9659a9555c63 100644
--- a/arch/arm64/kernel/hw_breakpoint.c
+++ b/arch/arm64/kernel/hw_breakpoint.c
@@ -654,7 +654,7 @@ static int breakpoint_handler(unsigned long unused, unsigned long esr,
perf_bp_event(bp, regs);
/* Do we need to handle the stepping? */
- if (is_default_overflow_handler(bp))
+ if (uses_default_overflow_handler(bp))
step = 1;
unlock:
rcu_read_unlock();
@@ -733,7 +733,7 @@ static u64 get_distance_from_watchpoint(unsigned long addr, u64 val,
static int watchpoint_report(struct perf_event *wp, unsigned long addr,
struct pt_regs *regs)
{
- int step = is_default_overflow_handler(wp);
+ int step = uses_default_overflow_handler(wp);
struct arch_hw_breakpoint *info = counter_arch_bp(wp);
info->trigger = addr;
diff --git a/include/linux/perf_event.h b/include/linux/perf_event.h
index ee8b9ecdc03b..f174b77437f5 100644
--- a/include/linux/perf_event.h
+++ b/include/linux/perf_event.h
@@ -1105,15 +1105,31 @@ extern int perf_event_output(struct perf_event *event,
struct pt_regs *regs);
static inline bool
-is_default_overflow_handler(struct perf_event *event)
+__is_default_overflow_handler(perf_overflow_handler_t overflow_handler)
{
- if (likely(event->overflow_handler == perf_event_output_forward))
+ if (likely(overflow_handler == perf_event_output_forward))
return true;
- if (unlikely(event->overflow_handler == perf_event_output_backward))
+ if (unlikely(overflow_handler == perf_event_output_backward))
return true;
return false;
}
+#define is_default_overflow_handler(event) \
+ __is_default_overflow_handler((event)->overflow_handler)
+
+#ifdef CONFIG_BPF_SYSCALL
+static inline bool uses_default_overflow_handler(struct perf_event *event)
+{
+ if (likely(is_default_overflow_handler(event)))
+ return true;
+
+ return __is_default_overflow_handler(event->orig_overflow_handler);
+}
+#else
+#define uses_default_overflow_handler(event) \
+ is_default_overflow_handler(event)
+#endif
+
extern void
perf_event_header__init_id(struct perf_event_header *header,
struct perf_sample_data *data,
--
2.30.2
