From: Oleg Nesterov <oleg@redhat.com>
To: Will Drewry <wad@chromium.org>
Cc: linux-kernel@vger.kernel.org, linux-arch@vger.kernel.org,
linux-doc@vger.kernel.org, kernel-hardening@lists.openwall.com,
netdev@vger.kernel.org, x86@kernel.org, arnd@arndb.de,
davem@davemloft.net, hpa@zytor.com, mingo@redhat.com,
peterz@infradead.org, rdunlap@xenotime.net,
mcgrathr@chromium.org, tglx@linutronix.de, luto@mit.edu,
eparis@redhat.com, serge.hallyn@canonical.com, djm@mindrot.org,
scarybeasts@gmail.com, indan@nul.nu, pmoore@redhat.com,
akpm@linux-foundation.org, corbet@lwn.net,
eric.dumazet@gmail.com, markus@chromium.org,
coreyb@linux.vnet.ibm.com, keescook@chromium.org,
Denys Vlasenko <dvlasenk@redhat.com>
Subject: Re: [PATCH v11 10/12] ptrace,seccomp: Add PTRACE_SECCOMP support
Date: Wed, 29 Feb 2012 18:09:33 +0100 [thread overview]
Message-ID: <20120229170933.GA6149@redhat.com> (raw)
In-Reply-To: <CABqD9hZLi416irXMMPmysYohrOn1gQjhjDyKTggU80Kd7ywvcA@mail.gmail.com>
On 02/29, Will Drewry wrote:
> On Wed, Feb 29, 2012 at 10:14 AM, Oleg Nesterov <oleg@redhat.com> wrote:
> > On 02/28, Will Drewry wrote:
> >>
> >> On Tue, Feb 28, 2012 at 11:04 AM, Will Drewry <wad@chromium.org> wrote:
> >> > On Tue, Feb 28, 2012 at 10:43 AM, Oleg Nesterov <oleg@redhat.com> wrote:
> >> >>
> >> >> Great. In this case this patch becomes really trivial. Just 2 defines
> >> >> in ptrace.h and the unconditional ptrace_event() under SECCOMP_RET_TRACE.
> >>
> >> hrm the only snag is that I can't then rely on TIF_SYSCALL_TRACE to
> >> ensure seccomp is in the slow-path. Right now, on x86, seccomp is
> >> slow-path, but it doesn't have to be to have the syscall and args.
> >> However, for ptrace to behavior properly, I believed it did need to be
> >> in the slow path. If SECCOMP_RET_TRACE doesn't rely on
> >> PTRACE_SYSCALL, then it introduces a need for seccomp to always be in
> >> the slow path or to flag (somehow) when it needs slow path.
> >
> > My understanding of this magic is very limited, and I'm afraid
> > I misunderstood... So please correct me.
> >
> > But what is the problem? system_call checks _TIF_WORK_SYSCALL_ENTRY
> > which includes _TIF_SECCOMP | _TIF_SYSCALL_TRACE, and jumps to
> > tracesys which does SAVE_REST.
> >
> > Anyway. secure_computing() is called by syscall_trace_enter() which
> > also calls tracehook_report_syscall_entry(). If SECCOMP_RET_TRACE
> > can't do ptrace_event() then why tracehook_report_syscall_entry() is
> > fine?
>
> Early on in this patch series, I was urged away from regviews (for
> many reasons), one of them was so that seccomp could, at some point,
> be fast-path'd like audit is for x86. (It may be on arm already, I'd
> need to check.) So I was hoping that I could avoid adding a slow-path
> dependency to the seccomp code.
Thanks, now I see what you meant.
> By adding a requirement for the
> slow-path in the form of ptrace_event(), the difficulty for making
> seccomp fast-path friendly is increased.
Yes. I do not know if this is really bad. I mean, I do not know how
much do we want the fast-path'd seccomp.
> (It could be possible to add
> a return code, e.g., return NEEDS_SLOW_PATH, which tells the fast path
> code to restart the handling at syscall_trace_enter, so maybe I am
> making a big deal out of nothing.)
Probably. Or SECCOMP_RET_TRACE can set TIF_NOTIFY_RESUME.
(Btw there is another alternative although imho PTRACE_EVENT_SECCOMP
looks better. SECCOMP_RET_TRACE can simply set TIF_SYSCALL_TRACE and
return, syscall_trace_enter() will report the syscall. If we make it
fast-path'ed, then TIF_NOTIFY_RESUME should trigger the slow path)
> I was hoping to avoid having TIF_SECCOMP imply the slow-path, but if
> that is the only sane way to integrate, then I can leave making it
> fast-path friendly as a future exercise.
>
> If I'm over-optimizing,
may be ;) but it is very possible I underestimate the problem.
I'd like to know what Roland thinks.
Oleg.
next prev parent reply other threads:[~2012-02-29 17:17 UTC|newest]
Thread overview: 53+ messages / expand[flat|nested] mbox.gz Atom feed top
2012-02-25 3:21 [PATCH v11 01/12] sk_run_filter: add support for custom load_pointer Will Drewry
2012-02-25 3:21 ` [PATCH v11 02/12] net/compat.c,linux/filter.h: share compat_sock_fprog Will Drewry
2012-02-25 3:21 ` [PATCH v11 03/12] seccomp: kill the seccomp_t typedef Will Drewry
2012-02-25 3:21 ` [PATCH v11 04/12] asm/syscall.h: add syscall_get_arch Will Drewry
2012-02-25 3:21 ` [PATCH v11 05/12] arch/x86: add syscall_get_arch to syscall.h Will Drewry
2012-02-25 3:21 ` [PATCH v11 06/12] seccomp: add system call filtering using BPF Will Drewry
2012-02-26 20:28 ` Kees Cook
2012-02-27 16:23 ` Will Drewry
2012-02-27 16:49 ` Eric Paris
2012-02-27 18:55 ` Kees Cook
2012-02-27 19:25 ` Eric Paris
2012-02-27 20:00 ` Kees Cook
2012-02-27 20:34 ` Eric Paris
2012-02-27 20:49 ` Kees Cook
2012-02-27 17:09 ` Oleg Nesterov
2012-02-27 19:54 ` Will Drewry
2012-02-27 20:15 ` Kees Cook
2012-02-28 15:13 ` Oleg Nesterov
2012-02-28 17:18 ` Will Drewry
2012-02-28 6:51 ` Indan Zupancic
2012-02-28 7:52 ` Kees Cook
2012-02-28 17:17 ` Will Drewry
2012-02-28 17:47 ` Markus Gutschke
2012-02-25 3:21 ` [PATCH v11 07/12] seccomp: add SECCOMP_RET_ERRNO Will Drewry
2012-02-25 20:20 ` Kees Cook
2012-02-27 16:22 ` Will Drewry
2012-02-27 17:11 ` Oleg Nesterov
2012-02-27 18:09 ` Kees Cook
2012-02-27 18:14 ` Oleg Nesterov
2012-02-27 18:35 ` Andrew Lutomirski
2012-02-27 19:14 ` Kees Cook
2012-02-27 19:54 ` Will Drewry
2012-02-25 3:21 ` [PATCH v11 08/12] signal, x86: add SIGSYS info and make it synchronous Will Drewry
2012-02-27 17:22 ` Oleg Nesterov
2012-02-27 17:34 ` Roland McGrath
2012-02-27 18:08 ` Oleg Nesterov
2012-02-27 20:24 ` Will Drewry
2012-02-28 16:02 ` Oleg Nesterov
2012-02-28 17:06 ` Will Drewry
2012-02-25 3:21 ` [PATCH v11 09/12] seccomp: Add SECCOMP_RET_TRAP Will Drewry
2012-02-25 3:21 ` [PATCH v11 10/12] ptrace,seccomp: Add PTRACE_SECCOMP support Will Drewry
2012-02-27 17:54 ` Oleg Nesterov
2012-02-27 19:47 ` Will Drewry
2012-02-28 16:43 ` Oleg Nesterov
2012-02-28 17:04 ` Will Drewry
2012-02-28 18:34 ` Will Drewry
2012-02-29 16:14 ` Oleg Nesterov
2012-02-29 16:33 ` Will Drewry
2012-02-29 17:09 ` Oleg Nesterov [this message]
2012-02-29 17:41 ` Roland McGrath
2012-02-29 17:51 ` Will Drewry
2012-02-25 3:21 ` [PATCH v11 11/12] x86: Enable HAVE_ARCH_SECCOMP_FILTER Will Drewry
2012-02-25 3:21 ` [PATCH v11 12/12] Documentation: prctl/seccomp_filter Will Drewry
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