From: Andy Lutomirski <luto@amacapital.net>
To: Kees Cook <keescook@chromium.org>
Cc: Oleg Nesterov <oleg@redhat.com>,
LKML <linux-kernel@vger.kernel.org>,
"Michael Kerrisk (man-pages)" <mtk.manpages@gmail.com>,
Alexei Starovoitov <ast@plumgrid.com>,
Andrew Morton <akpm@linux-foundation.org>,
Daniel Borkmann <dborkman@redhat.com>,
Will Drewry <wad@chromium.org>, Julien Tinnes <jln@chromium.org>,
David Drysdale <drysdale@google.com>,
Linux API <linux-api@vger.kernel.org>,
"x86@kernel.org" <x86@kernel.org>,
"linux-arm-kernel@lists.infradead.org"
<linux-arm-kernel@lists.infradead.org>,
linux-mips@linux-mips.org,
linux-arch <linux-arch@vger.kernel.org>,
linux-security-module <linux-security-module@vger.kernel.org>
Subject: Re: [PATCH v8 5/9] seccomp: split mode set routines
Date: Wed, 25 Jun 2014 09:10:32 -0700 [thread overview]
Message-ID: <CALCETrUBNmLnpa+LM91om2RSpR6SjupP-EdefzhU1Me4nv3Dfw@mail.gmail.com> (raw)
In-Reply-To: <CAGXu5jJkFxh4K=40xuh6tu3kUf4oJM8Dry+4upBdRieW3FNLgw@mail.gmail.com>
On Wed, Jun 25, 2014 at 7:51 AM, Kees Cook <keescook@chromium.org> wrote:
> On Wed, Jun 25, 2014 at 6:51 AM, Oleg Nesterov <oleg@redhat.com> wrote:
>> On 06/24, Kees Cook wrote:
>>>
>>> +static inline void seccomp_assign_mode(struct task_struct *task,
>>> + unsigned long seccomp_mode)
>>> +{
>>> + BUG_ON(!spin_is_locked(&task->sighand->siglock));
>>> +
>>> + task->seccomp.mode = seccomp_mode;
>>> + set_tsk_thread_flag(task, TIF_SECCOMP);
>>> +}
>>
>> OK, but unless task == current this can race with secure_computing().
>> I think this needs smp_mb__before_atomic() and secure_computing() needs
>> rmb() after test_bit(TIF_SECCOMP).
>>
>> Otherwise, can't __secure_computing() hit BUG() if it sees the old
>> mode == SECCOMP_MODE_DISABLED ?
>>
>> Or seccomp_run_filters() can see ->filters == NULL and WARN(),
>> smp_load_acquire() only serializes that LOAD with the subsequent memory
>> operations.
>
> Hm, actually, now I'm worried about smp_load_acquire() being too slow
> in run_filters().
>
> The ordering must be:
> - task->seccomp.filter must be valid before
> - task->seccomp.mode is set, which must be valid before
> - TIF_SECCOMP is set
>
> But I don't want to impact secure_computing(). What's the best way to
> make sure this ordering is respected?
Remove the ordering requirement, perhaps?
What if you moved mode into seccomp.filter? Then there would be
little reason to check TIF_SECCOMP from secure_computing; instead, you
could smp_load_acquire (or read_barrier_depends, maybe) seccomp.filter
from secure_computing and pass the result as a parameter to
__secure_computing. Or you could even remove the distinction between
secure_computing and __secure_computing -- it's essentially useless
anyway to split entry hook approaches like my x86 fastpath prototype.
--Andy
next prev parent reply other threads:[~2014-06-25 16:10 UTC|newest]
Thread overview: 53+ messages / expand[flat|nested] mbox.gz Atom feed top
2014-06-24 20:48 [PATCH v8 0/9] seccomp: add thread sync ability Kees Cook
2014-06-24 20:48 ` [PATCH v8 1/9] seccomp: create internal mode-setting function Kees Cook
2014-06-24 20:48 ` [PATCH v8 2/9] seccomp: split filter prep from check and apply Kees Cook
2014-06-24 20:48 ` [PATCH v8 3/9] seccomp: introduce writer locking Kees Cook
2014-06-25 14:03 ` Oleg Nesterov
2014-06-25 18:07 ` Oleg Nesterov
2014-06-25 18:29 ` Oleg Nesterov
2014-06-27 17:27 ` Kees Cook
2014-06-24 20:48 ` [PATCH v8 4/9] sched: move no_new_privs into new atomic flags Kees Cook
2014-06-25 13:43 ` Oleg Nesterov
2014-06-25 14:44 ` Kees Cook
2014-06-24 20:48 ` [PATCH v8 5/9] seccomp: split mode set routines Kees Cook
2014-06-25 13:51 ` Oleg Nesterov
2014-06-25 14:51 ` Kees Cook
2014-06-25 16:10 ` Andy Lutomirski [this message]
2014-06-25 16:54 ` Kees Cook
2014-06-25 17:03 ` Andy Lutomirski
2014-06-25 17:32 ` Oleg Nesterov
2014-06-25 17:38 ` Andy Lutomirski
2014-06-25 17:51 ` Oleg Nesterov
2014-06-25 18:00 ` Kees Cook
2014-06-25 18:07 ` Andy Lutomirski
2014-06-27 18:33 ` Kees Cook
2014-06-27 18:39 ` Andy Lutomirski
2014-06-27 18:52 ` Kees Cook
2014-06-27 18:56 ` Andy Lutomirski
2014-06-27 19:04 ` Kees Cook
2014-06-27 19:11 ` Andy Lutomirski
2014-06-27 19:27 ` Oleg Nesterov
2014-06-27 19:31 ` Andy Lutomirski
2014-06-27 19:55 ` Oleg Nesterov
2014-06-27 20:08 ` Andy Lutomirski
2014-06-27 20:56 ` Kees Cook
2014-06-25 17:00 ` Oleg Nesterov
2014-06-24 20:48 ` [PATCH v8 6/9] seccomp: add "seccomp" syscall Kees Cook
2014-06-24 20:48 ` [PATCH v8 7/9] ARM: add seccomp syscall Kees Cook
2014-06-24 20:48 ` [PATCH v8 8/9] MIPS: " Kees Cook
2014-06-24 20:48 ` [PATCH v8 9/9] seccomp: implement SECCOMP_FILTER_FLAG_TSYNC Kees Cook
2014-06-25 14:21 ` Oleg Nesterov
2014-06-25 15:08 ` Kees Cook
2014-06-25 16:52 ` Oleg Nesterov
2014-06-25 17:09 ` Kees Cook
2014-06-25 17:24 ` Oleg Nesterov
2014-06-25 17:40 ` Andy Lutomirski
2014-06-25 17:57 ` Kees Cook
2014-06-25 18:09 ` Andy Lutomirski
2014-06-25 18:25 ` Kees Cook
2014-06-25 18:20 ` Oleg Nesterov
2014-06-25 18:31 ` Kees Cook
2014-06-24 20:56 ` [PATCH v8 1/1] man-pages: seccomp.2: document syscall Kees Cook
2014-06-25 13:04 ` One Thousand Gnomes
2014-06-25 15:10 ` Kees Cook
2014-06-25 17:54 ` Michael Kerrisk (man-pages)
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