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.

ONOleg Nesterov committed 6 years ago