[BUG kretprobes] kretprobe triggers General Protection Faults

[Mathieu Desnoyers]

Hi,

I had a bug report[1] from a user trying to add a kretprobe on the system
call entry code path:

arch/x86/kernel/entry_64.S:

ffffffff813dffe2 <system_call_fastpath+0x16>:
        cmpl $__NR_syscall_max,%eax
#endif
        ja badsys
        movq %r10,%rcx
        call *sys_call_table(,%rax,8)  # XXX:    rip relative
        movq %rax,RAX-ARGOFFSET(%rsp)   <--- return address pointing here

And all hell breaks loose (various types of faults, machine reboots,
applications exit randomly, etc.). I understand that this code path
is not marked as unsafe against kprobes, and I tested that a kprobes
indeed works fine there. However, kretprobes probably presumes a function
stack layout that is just not valid for the syscall entry routine.

Any thoughts on how kretprobes should handle this ?

Thanks,

Mathieu

[1] http://bugs.lttng.org/issues/687

-- 
Mathieu Desnoyers
EfficiOS Inc.
http://www.efficios.com
--
To unsubscribe from this list: send the line "unsubscribe linux-kernel" in
the body of a message to majordomo@xxxxxxxxxxxxxxx
More majordomo info at  http://vger.kernel.org/majordomo-info.html
Please read the FAQ at  http://www.tux.org/lkml/