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authorOleg Nesterov <oleg@redhat.com>2020-07-23 17:44:20 +0200
committerIngo Molnar <mingo@kernel.org>2020-07-24 15:38:37 +0200
commitfe5ed7ab99c656bd2f5b79b49df0e9ebf2cead8a (patch)
tree5d42a77cb0c455ff620d5b769fdfadf9afc52c42 /kernel/events
parentf37e99aca03f63aa3f2bd13ceaf769455d12c4b0 (diff)
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
Diffstat (limited to 'kernel/events')
-rw-r--r--kernel/events/uprobes.c2
1 files changed, 1 insertions, 1 deletions
diff --git a/kernel/events/uprobes.c b/kernel/events/uprobes.c
index bb0862873dba..5f8b0c52fd2e 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