• Oleg Nesterov's avatar
    uprobes: Change handle_swbp() to send SIGTRAP with si_code=SI_KERNEL, to fix GDB regression · fe5ed7ab
    Oleg Nesterov authored
    
    
    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: default avatarAaron Merey <amerey@redhat.com>
    Signed-off-by: default avatarOleg Nesterov <oleg@redhat.com>
    Signed-off-by: default avatarIngo Molnar <mingo@kernel.org>
    Reviewed-by: default avatarSrikar Dronamraju <srikar@linux.vnet.ibm.com>
    Cc: stable@vger.kernel.org
    Link: https://lore.kernel.org/r/20200723154420.GA32043@redhat.com
    fe5ed7ab
uprobes.c 57 KB