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Subject[PATCH 4.4 11/54] uprobes: Change handle_swbp() to send SIGTRAP with si_code=SI_KERNEL, to fix GDB regression
From: Oleg Nesterov <>

commit fe5ed7ab99c656bd2f5b79b49df0e9ebf2cead8a upstream.

If a tracee is uprobed and it hits int3 inserted by debugger, handle_swbp()
does send_sig(SIGTRAP, current, 0) which means si_code == SI_USER. This used
to work when this code was written, but then GDB started to validate si_code
and now it simply can't use breakpoints if the tracee has an active uprobe:

# cat test.c
void unused_func(void)
int main(void)
return 0;

# gcc -g test.c -o test
# perf probe -x ./test -a unused_func
# perf record -e probe_test:unused_func gdb ./test -ex run
GNU gdb (GDB)
Program received signal SIGTRAP, Trace/breakpoint trap.
0x00007ffff7ddf909 in dl_main () from /lib64/

The tracee hits the internal breakpoint inserted by GDB to monitor shared
library events but GDB misinterprets this SIGTRAP and reports a signal.

Change handle_swbp() to use force_sig(SIGTRAP), this matches do_int3_user()
and fixes the problem.

This is the minimal fix for -stable, arch/x86/kernel/uprobes.c is equally
wrong; it should use send_sigtrap(TRAP_TRACE) instead of send_sig(SIGTRAP),
but this doesn't confuse GDB and needs another x86-specific patch.

Reported-by: Aaron Merey <>
Signed-off-by: Oleg Nesterov <>
Signed-off-by: Ingo Molnar <>
Reviewed-by: Srikar Dronamraju <>
Signed-off-by: Greg Kroah-Hartman <>

kernel/events/uprobes.c | 2 +-
1 file changed, 1 insertion(+), 1 deletion(-)

--- a/kernel/events/uprobes.c
+++ b/kernel/events/uprobes.c
@@ -1875,7 +1875,7 @@ static void handle_swbp(struct pt_regs *
if (!uprobe) {
if (is_swbp > 0) {
/* No matching uprobe; signal SIGTRAP. */
- send_sig(SIGTRAP, current, 0);
+ force_sig(SIGTRAP, current);
} else {
* Either we raced with uprobe_unregister() or we can't

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