| From 6bb6a129588eea5ccbde2da3264f277bb7bb78eb Mon Sep 17 00:00:00 2001 |
| From: Oleg Nesterov <oleg@redhat.com> |
| Date: Thu, 23 Jul 2020 17:44:20 +0200 |
| Subject: [PATCH] uprobes: Change handle_swbp() to send SIGTRAP with |
| si_code=SI_KERNEL, to fix GDB regression |
| |
| 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: Paul Gortmaker <paul.gortmaker@windriver.com> |
| |
| diff --git a/kernel/events/uprobes.c b/kernel/events/uprobes.c |
| index ccfeb313be21..673044edd9ad 100644 |
| --- a/kernel/events/uprobes.c |
| +++ b/kernel/events/uprobes.c |
| @@ -2153,7 +2153,7 @@ 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, current); |
| } else { |
| /* |
| * Either we raced with uprobe_unregister() or we can't |
| -- |
| 2.27.0 |
| |