The following commit has been merged into the perf/urgent branch of tip:

Commit-ID: fe5ed7ab99c656bd2f5b79b49df0e9ebf2cead8a Gitweb: https://git.kernel.org/tip/fe5ed7ab99c656bd2f5b79b49df0e9ebf2cead8a Author: Oleg Nesterov oleg@redhat.com AuthorDate: Thu, 23 Jul 2020 17:44:20 +02:00 Committer: Ingo Molnar mingo@kernel.org CommitterDate: Fri, 24 Jul 2020 15:38:37 +02:00

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

diff --git a/kernel/events/uprobes.c b/kernel/events/uprobes.c index bb08628..5f8b0c5 100644 --- a/kernel/events/uprobes.c +++ b/kernel/events/uprobes.c @@ -2199,7 +2199,7 @@ static void handle_swbp(struct pt_regs *regs) if (!uprobe) { if (is_swbp > 0) { /* No matching uprobe; signal SIGTRAP. */ - send_sig(SIGTRAP, current, 0); + force_sig(SIGTRAP); } else { /* * Either we raced with uprobe_unregister() or we can't