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From: Oleg Nesterov <oleg@redhat.com>
To: Kees Cook <keescook@chromium.org>
Cc: LKML <linux-kernel@vger.kernel.org>,
	Andy Lutomirski <luto@amacapital.net>,
	"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 19:00:39 +0200	[thread overview]
Message-ID: <20140625170039.GB14720@redhat.com> (raw)
In-Reply-To: <CAGXu5jJkFxh4K=40xuh6tu3kUf4oJM8Dry+4upBdRieW3FNLgw@mail.gmail.com>

On 06/25, Kees Cook 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?

Cough, confused... can't understand even after I read the email from Andy.

We do not care if __secure_computing() misses the recently added filter,
this can happen anyway, whatever we do.

seccomp.mode is frozen after we set it != SECCOMP_MODE_DISABLED.

So we should only worry if set_tsk_thread_flag(TIF_SECCOMP) actually
changes this bit and makes __secure_computing() possible. If we add
smp_mb__before_atomic() into seccomp_assign_mode() and rmb() at the
start of __secure_computing() everything should be fine?

Oleg.

  parent reply	other threads:[~2014-06-25 17:00 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
2014-06-25 16:54         ` Kees Cook
     [not found]           ` <CAGXu5j+J11zJnuFR8bYKAXizAHhCx4R+uJE_QH6zC3q2udkpaQ-JsoAwUIsXosN+BqQ9rBEUg@public.gmane.org>
2014-06-25 17:03             ` Andy Lutomirski
2014-06-25 17:32               ` Oleg Nesterov
     [not found]                 ` <20140625173245.GA17695-H+wXaHxf7aLQT0dZR+AlfA@public.gmane.org>
2014-06-25 17:38                   ` Andy Lutomirski
2014-06-25 17:51                     ` Oleg Nesterov
2014-06-25 18:00                       ` Kees Cook
     [not found]                         ` <CAGXu5jL17k6=GXju6x+eLU20FMwBHhnuRiHoQD1Bzj_EmpiKjg-JsoAwUIsXosN+BqQ9rBEUg@public.gmane.org>
2014-06-25 18:07                           ` Andy Lutomirski
2014-06-27 18:33                             ` Kees Cook
2014-06-27 18:39                               ` Andy Lutomirski
     [not found]                                 ` <CALCETrUPxTxseJ=sOhD9CyJPtOqCR5sL8yx7KezLmLZcFSFNMA-JsoAwUIsXosN+BqQ9rBEUg@public.gmane.org>
2014-06-27 18:52                                   ` Kees Cook
2014-06-27 18:56                                     ` Andy Lutomirski
2014-06-27 19:04                                       ` Kees Cook
     [not found]                                         ` <CAGXu5jL5rN6=2-SwHiiEVuGVain-T7Ucg2PsN7u08vQ5Rxz6Mg-JsoAwUIsXosN+BqQ9rBEUg@public.gmane.org>
2014-06-27 19:11                                           ` Andy Lutomirski
2014-06-27 19:27                               ` Oleg Nesterov
     [not found]                                 ` <20140627192753.GA30752-H+wXaHxf7aLQT0dZR+AlfA@public.gmane.org>
2014-06-27 19:31                                   ` Andy Lutomirski
2014-06-27 19:55                                     ` Oleg Nesterov
     [not found]                                       ` <20140627195559.GA31661-H+wXaHxf7aLQT0dZR+AlfA@public.gmane.org>
2014-06-27 20:08                                         ` Andy Lutomirski
2014-06-27 20:56                                         ` Kees Cook
2014-06-25 17:00       ` Oleg Nesterov [this message]
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
     [not found]         ` <20140625165209.GA14720-H+wXaHxf7aLQT0dZR+AlfA@public.gmane.org>
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
     [not found]                   ` <20140625182012.GA19437-H+wXaHxf7aLQT0dZR+AlfA@public.gmane.org>
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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