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   1 From fe5ed7ab99c656bd2f5b79b49df0e9ebf2cead8a Mon Sep 17 00:00:00 2001
   2 From: Oleg Nesterov <oleg@redhat.com>
   3 Date: Thu, 23 Jul 2020 17:44:20 +0200
   4 Subject: uprobes: Change handle_swbp() to send SIGTRAP with si_code=SI_KERNEL, to fix GDB regression
   5
   6 From: Oleg Nesterov <oleg@redhat.com>
   7
   8 commit fe5ed7ab99c656bd2f5b79b49df0e9ebf2cead8a upstream.
   9
  10 If a tracee is uprobed and it hits int3 inserted by debugger, handle_swbp()
  11 does send_sig(SIGTRAP, current, 0) which means si_code == SI_USER. This used
  12 to work when this code was written, but then GDB started to validate si_code
  13 and now it simply can't use breakpoints if the tracee has an active uprobe:
  14
  15         # cat test.c
  16         void unused_func(void)
  17         {
  18         }
  19         int main(void)
  20         {
  21                 return 0;
  22         }
  23
  24         # gcc -g test.c -o test
  25         # perf probe -x ./test -a unused_func
  26         # perf record -e probe_test:unused_func gdb ./test -ex run
  27         GNU gdb (GDB) 10.0.50.20200714-git
  28         ...
  29         Program received signal SIGTRAP, Trace/breakpoint trap.
  30         0x00007ffff7ddf909 in dl_main () from /lib64/ld-linux-x86-64.so.2
  31         (gdb)
  32
  33 The tracee hits the internal breakpoint inserted by GDB to monitor shared
  34 library events but GDB misinterprets this SIGTRAP and reports a signal.
  35
  36 Change handle_swbp() to use force_sig(SIGTRAP), this matches do_int3_user()
  37 and fixes the problem.
  38
  39 This is the minimal fix for -stable, arch/x86/kernel/uprobes.c is equally
  40 wrong; it should use send_sigtrap(TRAP_TRACE) instead of send_sig(SIGTRAP),
  41 but this doesn't confuse GDB and needs another x86-specific patch.
  42
  43 Reported-by: Aaron Merey <amerey@redhat.com>
  44 Signed-off-by: Oleg Nesterov <oleg@redhat.com>
  45 Signed-off-by: Ingo Molnar <mingo@kernel.org>
  46 Reviewed-by: Srikar Dronamraju <srikar@linux.vnet.ibm.com>
  47 Cc: stable@vger.kernel.org
  48 Link: https://lore.kernel.org/r/20200723154420.GA32043@redhat.com
  49 Signed-off-by: Greg Kroah-Hartman <gregkh@linuxfoundation.org>
  50
  51 ---
  52  kernel/events/uprobes.c |    2 +-
  53  1 file changed, 1 insertion(+), 1 deletion(-)
  54
  55 --- a/kernel/events/uprobes.c
  56 +++ b/kernel/events/uprobes.c
  57 @@ -2205,7 +2205,7 @@ static void handle_swbp(struct pt_regs *
  58         if (!uprobe) {
  59                 if (is_swbp > 0) {
  60                         /* No matching uprobe; signal SIGTRAP. */
  61 -                       send_sig(SIGTRAP, current, 0);
  62 +                       force_sig(SIGTRAP);
  63                 } else {
  64                         /*
  65                          * Either we raced with uprobe_unregister() or we can't