a method to distinguish between syscall-enter/exit-stop

[Kees Cook]

On Fri, Feb 6, 2015 at 3:17 PM, Dmitry V. Levin <ldv at altlinux.org> wrote:
> On Fri, Feb 06, 2015 at 12:07:03PM -0800, Kees Cook wrote:
>> On Fri, Feb 6, 2015 at 11:32 AM, Andy Lutomirski <luto at amacapital.net> wrote:
>> > On Fri, Feb 6, 2015 at 11:23 AM, Kees Cook <keescook at chromium.org> wrote:
> [...]
>> >> And an unrelated thought:
>> >>
>> >> 3) Can't we find some way to fix the inability of a ptracer to
>> >> distinguish between syscall-enter-stop and syscall-exit-stop?
>> >
>> > Couldn't we add PTRACE_O_TRACESYSENTRY and PTRACE_O_TRACESYSEXIT along
>> > the lines of PTRACE_O_TRACESYSGOOD?
>>
>> That might be a nice idea. I haven't written a test to see, but what
>> does PTRACE_GETEVENTMSG return on syscall-enter/exit-stop?
>
> The value returned by PTRACE_GETEVENTMSG is the value set along with the
> latest PTRACE_EVENT_*.
> In case of syscall-enter/exit-stop (which is not a PTRACE_EVENT_*),
> there is no particular value set for PTRACE_GETEVENTMSG.

Could we define one to help distinguish?

-Kees

-- 
Kees Cook
Chrome OS Security