From: Oleg Nesterov oleg@redhat.com
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) 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: Aaron Merey amerey@redhat.com Signed-off-by: Oleg Nesterov oleg@redhat.com Signed-off-by: Ingo Molnar mingo@kernel.org Reviewed-by: Srikar Dronamraju srikar@linux.vnet.ibm.com Cc: stable@vger.kernel.org Link: https://lore.kernel.org/r/20200723154420.GA32043@redhat.com Signed-off-by: Greg Kroah-Hartman gregkh@linuxfoundation.org
--- kernel/events/uprobes.c | 2 +- 1 file changed, 1 insertion(+), 1 deletion(-)
--- a/kernel/events/uprobes.c +++ b/kernel/events/uprobes.c @@ -1885,7 +1885,7 @@ 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