From: ldv@altlinux•org (Dmitry V. Levin)
To: linux-arm-kernel@lists•infradead.org
Subject: a method to distinguish between syscall-enter/exit-stop
Date: Sat, 7 Feb 2015 06:04:47 +0300 [thread overview]
Message-ID: <20150207030447.GA4930@altlinux.org> (raw)
In-Reply-To: <CAGXu5jKHkJcnpbiuYY8BVX0-wOEUDFMx7r8_HJJe2ZDT8p3uvQ@mail.gmail.com>
On Fri, Feb 06, 2015 at 05:07:41PM -0800, Kees Cook wrote:
> On Fri, Feb 6, 2015 at 3:17 PM, Dmitry V. Levin <ldv@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@amacapital•net> wrote:
> >> > On Fri, Feb 6, 2015 at 11:23 AM, Kees Cook <keescook@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?
I suppose we could define one, but performing extra PTRACE_GETEVENTMSG
for every syscall-stop may be too expensive.
For example, strace makes about 4.5 syscalls per syscall-stop.
The minimum is 4 syscalls: wait4, PTRACE_GETREGSET, write, and PTRACE_SYSCALL;
processing some syscall-stops may require additional process_vm_readv calls.
That is, forcing strace to make extra PTRACE_GETEVENTMSG per syscall-stop
would result to about 20% more syscalls per syscall-stop, that is a
noticeable cost.
A better alternative is to define an event that wouldn't require this
extra PTRACE_GETEVENTMSG per syscall-stop. For example, it could be a
PTRACE_EVENT_SYSCALL_ENTRY and/or PTRACE_EVENT_SYSCALL_EXIT. In practice,
adding just one of these two events would be enough to distinguish two
kinds of syscall-stops. Adding two events would look less surprising,
though.
If the decision would be to add both events, I'd recommend adding just one
new option to cover both events - there is a room only for 32 different
PTRACE_O_* options.
--
ldv
next prev parent reply other threads:[~2015-02-07 3:04 UTC|newest]
Thread overview: 28+ messages / expand[flat|nested] mbox.gz Atom feed top
2014-09-05 22:13 [PATCH v5 0/5] x86: two-phase syscall tracing and seccomp fastpath Andy Lutomirski
2014-09-05 22:13 ` [PATCH v5 1/5] x86,x32,audit: Fix x32's AUDIT_ARCH wrt audit Andy Lutomirski
2014-09-05 22:13 ` [PATCH v5 2/5] x86,entry: Only call user_exit if TIF_NOHZ Andy Lutomirski
2014-09-05 22:13 ` [PATCH v5 3/5] x86: Split syscall_trace_enter into two phases Andy Lutomirski
2015-02-05 21:19 ` Dmitry V. Levin
2015-02-05 21:27 ` Kees Cook
2015-02-05 21:40 ` Dmitry V. Levin
2015-02-05 21:52 ` Andy Lutomirski
2015-02-05 23:12 ` Kees Cook
2015-02-05 23:39 ` Dmitry V. Levin
2015-02-05 23:49 ` Kees Cook
2015-02-06 0:09 ` Andy Lutomirski
2015-02-06 2:32 ` Dmitry V. Levin
2015-02-06 2:38 ` Andy Lutomirski
2015-02-06 19:23 ` Kees Cook
2015-02-06 19:32 ` Andy Lutomirski
2015-02-06 20:07 ` Kees Cook
2015-02-06 20:12 ` Andy Lutomirski
2015-02-06 20:16 ` Kees Cook
2015-02-06 20:20 ` Andy Lutomirski
2015-02-06 23:17 ` a method to distinguish between syscall-enter/exit-stop Dmitry V. Levin
2015-02-07 1:07 ` Kees Cook
2015-02-07 3:04 ` Dmitry V. Levin [this message]
2015-02-06 20:11 ` [PATCH v5 3/5] x86: Split syscall_trace_enter into two phases H. Peter Anvin
2014-09-05 22:13 ` [PATCH v5 4/5] x86_64, entry: Treat regs->ax the same in fastpath and slowpath syscalls Andy Lutomirski
2014-09-05 22:13 ` [PATCH v5 5/5] x86_64, entry: Use split-phase syscall_trace_enter for 64-bit syscalls Andy Lutomirski
2014-09-08 19:29 ` [PATCH v5 0/5] x86: two-phase syscall tracing and seccomp fastpath Kees Cook
2014-09-08 19:49 ` H. Peter Anvin
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