Commit fe5ed7ab authored by Oleg Nesterov's avatar Oleg Nesterov Committed by Ingo Molnar
Browse files

uprobes: Change handle_swbp() to send SIGTRAP with si_code=SI_KERNEL, to fix GDB regression



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) 10.0.50.20200714-git
	...
	Program received signal SIGTRAP, Trace/breakpoint trap.
	0x00007ffff7ddf909 in dl_main () from /lib64/ld-linux-x86-64.so.2
	(gdb)

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: default avatarAaron Merey <amerey@redhat.com>
Signed-off-by: default avatarOleg Nesterov <oleg@redhat.com>
Signed-off-by: default avatarIngo Molnar <mingo@kernel.org>
Reviewed-by: default avatarSrikar Dronamraju <srikar@linux.vnet.ibm.com>
Cc: stable@vger.kernel.org
Link: https://lore.kernel.org/r/20200723154420.GA32043@redhat.com
parent f37e99ac
...@@ -2199,7 +2199,7 @@ static void handle_swbp(struct pt_regs *regs) ...@@ -2199,7 +2199,7 @@ static void handle_swbp(struct pt_regs *regs)
if (!uprobe) { if (!uprobe) {
if (is_swbp > 0) { if (is_swbp > 0) {
/* No matching uprobe; signal SIGTRAP. */ /* No matching uprobe; signal SIGTRAP. */
send_sig(SIGTRAP, current, 0); force_sig(SIGTRAP);
} else { } else {
/* /*
* Either we raced with uprobe_unregister() or we can't * Either we raced with uprobe_unregister() or we can't
......
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