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From: Kees Cook <keescook@chromium.org>
To: Jann Horn <jannh@google.com>
Cc: YiFei Zhu <zhuyifei1999@gmail.com>,
	Linux Containers <containers@lists.linux-foundation.org>,
	YiFei Zhu <yifeifz2@illinois.edu>, bpf <bpf@vger.kernel.org>,
	kernel list <linux-kernel@vger.kernel.org>,
	Aleksa Sarai <cyphar@cyphar.com>,
	Andrea Arcangeli <aarcange@redhat.com>,
	Andy Lutomirski <luto@amacapital.net>,
	David Laight <David.Laight@aculab.com>,
	Dimitrios Skarlatos <dskarlat@cs.cmu.edu>,
	Giuseppe Scrivano <gscrivan@redhat.com>,
	Hubertus Franke <frankeh@us.ibm.com>,
	Jack Chen <jianyan2@illinois.edu>,
	Josep Torrellas <torrella@illinois.edu>,
	Tianyin Xu <tyxu@illinois.edu>,
	Tobin Feldman-Fitzthum <tobin@ibm.com>,
	Tycho Andersen <tycho@tycho.pizza>,
	Valentin Rothberg <vrothber@redhat.com>,
	Will Drewry <wad@chromium.org>
Subject: Re: [PATCH v3 seccomp 2/5] seccomp/cache: Add "emulator" to check if filter is constant allow
Date: Wed, 30 Sep 2020 15:49:01 -0700	[thread overview]
Message-ID: <202009301546.6B7D648F57@keescook> (raw)
In-Reply-To: <CAG48ez0Njm0oS+9k-cgUqzyUWXV=cHPope2Xe9vVNPUVZ1PB4w@mail.gmail.com>

On Thu, Oct 01, 2020 at 12:24:32AM +0200, Jann Horn wrote:
> On Wed, Sep 30, 2020 at 5:20 PM YiFei Zhu <zhuyifei1999@gmail.com> wrote:
> > SECCOMP_CACHE_NR_ONLY will only operate on syscalls that do not
> > access any syscall arguments or instruction pointer. To facilitate
> > this we need a static analyser to know whether a filter will
> > return allow regardless of syscall arguments for a given
> > architecture number / syscall number pair. This is implemented
> > here with a pseudo-emulator, and stored in a per-filter bitmap.
> >
> > Each common BPF instruction are emulated. Any weirdness or loading
> > from a syscall argument will cause the emulator to bail.
> >
> > The emulation is also halted if it reaches a return. In that case,
> > if it returns an SECCOMP_RET_ALLOW, the syscall is marked as good.
> >
> > Emulator structure and comments are from Kees [1] and Jann [2].
> >
> > Emulation is done at attach time. If a filter depends on more
> > filters, and if the dependee does not guarantee to allow the
> > syscall, then we skip the emulation of this syscall.
> >
> > [1] https://lore.kernel.org/lkml/20200923232923.3142503-5-keescook@chromium.org/
> > [2] https://lore.kernel.org/lkml/CAG48ez1p=dR_2ikKq=xVxkoGg0fYpTBpkhJSv1w-6BG=76PAvw@mail.gmail.com/
> [...]
> > +static void seccomp_cache_prepare_bitmap(struct seccomp_filter *sfilter,
> > +                                        void *bitmap, const void *bitmap_prev,
> > +                                        size_t bitmap_size, int arch)
> > +{
> > +       struct sock_fprog_kern *fprog = sfilter->prog->orig_prog;
> > +       struct seccomp_data sd;
> > +       int nr;
> > +
> > +       for (nr = 0; nr < bitmap_size; nr++) {
> > +               if (bitmap_prev && !test_bit(nr, bitmap_prev))
> > +                       continue;
> > +
> > +               sd.nr = nr;
> > +               sd.arch = arch;
> > +
> > +               if (seccomp_emu_is_const_allow(fprog, &sd))
> > +                       set_bit(nr, bitmap);
> 
> set_bit() is atomic, but since we only do this at filter setup, before
> the filter becomes globally visible, we don't need atomicity here. So
> this should probably use __set_bit() instead.

Oh yes, excellent point! That will speed this up a bit. When you do
this, please include a comment here describing why its safe to do it
non-atomic. :)

-- 
Kees Cook

  reply	other threads:[~2020-09-30 22:49 UTC|newest]

Thread overview: 141+ messages / expand[flat|nested]  mbox.gz  Atom feed  top
     [not found] <cover.1600661418.git.yifeifz2@illinois.edu>
2020-09-21  8:30 ` [RFC PATCH seccomp 0/2] seccomp: Add bitmap cache of arg-independent filter results that allow syscalls Christian Brauner
2020-09-21  8:44   ` YiFei Zhu
     [not found] ` <20200921135115.GC3794348@cisco>
2020-09-21 15:27   ` YiFei Zhu
2020-09-21 16:39     ` Tycho Andersen
2020-09-21 22:57       ` YiFei Zhu
     [not found] ` <6af89348c08a4820039e614a090d35aa1583acff.1600661419.git.yifeifz2@illinois.edu>
2020-09-21 17:47   ` [RFC PATCH seccomp 1/2] seccomp/cache: Add "emulator" to check if filter is arg-dependent Jann Horn
2020-09-21 18:38     ` Jann Horn
2020-09-21 23:44     ` YiFei Zhu
2020-09-22  0:25       ` Jann Horn
2020-09-22  0:47         ` YiFei Zhu
     [not found] ` <b792335294ee5598d0fb42702a49becbce2f925f.1600661419.git.yifeifz2@illinois.edu>
2020-09-21 18:08   ` [RFC PATCH seccomp 2/2] seccomp/cache: Cache filter results that allow syscalls Jann Horn
2020-09-21 22:50     ` YiFei Zhu
2020-09-21 22:57       ` Jann Horn
2020-09-21 23:08         ` YiFei Zhu
2020-09-25  0:01   ` [PATCH v2 seccomp 2/6] asm/syscall.h: Add syscall_arches[] array Kees Cook
2020-09-25  0:15     ` Jann Horn
2020-09-25  0:18       ` Al Viro
2020-09-25  0:24         ` Jann Horn
2020-09-25  1:27     ` YiFei Zhu
2020-09-25  3:09       ` Kees Cook
2020-09-25  3:28         ` YiFei Zhu
2020-09-25 16:39           ` YiFei Zhu
2020-09-21 19:16 ` [RFC PATCH seccomp 0/2] seccomp: Add bitmap cache of arg-independent filter results that allow syscalls Jann Horn
     [not found]   ` <OF8837FC1A.5C0D4D64-ON852585EA.006B677F-852585EA.006BA663@notes.na.collabserv.com>
2020-09-21 19:45     ` Jann Horn
2020-09-24 12:06 ` [PATCH seccomp 0/6] " YiFei Zhu
2020-09-24 12:06   ` [PATCH seccomp 1/6] seccomp: Move config option SECCOMP to arch/Kconfig YiFei Zhu
2020-09-24 12:06     ` YiFei Zhu
2020-09-24 12:06   ` [PATCH seccomp 2/6] asm/syscall.h: Add syscall_arches[] array YiFei Zhu
2020-09-24 12:06   ` [PATCH seccomp 3/6] seccomp/cache: Add "emulator" to check if filter is arg-dependent YiFei Zhu
2020-09-24 12:06   ` [PATCH seccomp 4/6] seccomp/cache: Lookup syscall allowlist for fast path YiFei Zhu
2020-09-24 12:06   ` [PATCH seccomp 5/6] selftests/seccomp: Compare bitmap vs filter overhead YiFei Zhu
2020-09-24 12:06   ` [PATCH seccomp 6/6] seccomp/cache: Report cache data through /proc/pid/seccomp_cache YiFei Zhu
2020-09-24 12:44   ` [PATCH v2 seccomp 0/6] seccomp: Add bitmap cache of arg-independent filter results that allow syscalls YiFei Zhu
2020-09-24 12:44     ` [PATCH v2 seccomp 1/6] seccomp: Move config option SECCOMP to arch/Kconfig YiFei Zhu
2020-09-24 19:11       ` Kees Cook
2020-10-27  9:52       ` Geert Uytterhoeven
2020-10-27 19:08         ` YiFei Zhu
2020-10-28  0:06         ` Kees Cook
2020-10-28  8:18           ` Geert Uytterhoeven
2020-10-28  9:34             ` Jann Horn
2020-09-24 12:44     ` [PATCH v2 seccomp 2/6] asm/syscall.h: Add syscall_arches[] array YiFei Zhu
2020-09-24 13:47       ` David Laight
2020-09-24 14:16         ` YiFei Zhu
2020-09-24 14:20           ` David Laight
2020-09-24 14:37             ` YiFei Zhu
2020-09-24 16:02               ` YiFei Zhu
2020-09-24 12:44     ` [PATCH v2 seccomp 3/6] seccomp/cache: Add "emulator" to check if filter is arg-dependent YiFei Zhu
2020-09-24 23:25       ` Kees Cook
2020-09-25  3:04         ` YiFei Zhu
2020-09-25 16:45           ` YiFei Zhu
2020-09-25 19:42             ` Kees Cook
2020-09-25 19:51               ` Andy Lutomirski
2020-09-25 20:37                 ` Kees Cook
2020-09-25 21:07                   ` Andy Lutomirski
2020-09-25 23:49                     ` Kees Cook
2020-09-26  0:34                       ` Andy Lutomirski
2020-09-26  1:23                     ` YiFei Zhu
2020-09-26  2:47                       ` Andy Lutomirski
2020-09-26  4:35                         ` Kees Cook
2020-09-24 12:44     ` [PATCH v2 seccomp 4/6] seccomp/cache: Lookup syscall allowlist for fast path YiFei Zhu
2020-09-24 23:46       ` Kees Cook
2020-09-25  1:55         ` YiFei Zhu
2020-09-24 12:44     ` [PATCH v2 seccomp 5/6] selftests/seccomp: Compare bitmap vs filter overhead YiFei Zhu
2020-09-24 23:47       ` Kees Cook
2020-09-25  1:35         ` YiFei Zhu
2020-09-24 12:44     ` [PATCH v2 seccomp 6/6] seccomp/cache: Report cache data through /proc/pid/seccomp_cache YiFei Zhu
2020-09-24 23:56       ` Kees Cook
2020-09-25  3:11         ` YiFei Zhu
2020-09-25  3:26           ` Kees Cook
2020-09-30 15:19 ` [PATCH v3 seccomp 0/5] seccomp: Add bitmap cache of constant allow filter results YiFei Zhu
2020-09-30 15:19   ` [PATCH v3 seccomp 1/5] x86: Enable seccomp architecture tracking YiFei Zhu
2020-09-30 21:21     ` Kees Cook
2020-09-30 21:33       ` Jann Horn
2020-09-30 22:53         ` Kees Cook
2020-09-30 23:15           ` Jann Horn
2020-09-30 15:19   ` [PATCH v3 seccomp 2/5] seccomp/cache: Add "emulator" to check if filter is constant allow YiFei Zhu
2020-09-30 22:24     ` Jann Horn
2020-09-30 22:49       ` Kees Cook [this message]
2020-10-01 11:28       ` YiFei Zhu
2020-10-01 21:08         ` Jann Horn
2020-09-30 22:40     ` Kees Cook
2020-10-01 11:52       ` YiFei Zhu
2020-10-01 21:05         ` Kees Cook
2020-10-02 11:08           ` YiFei Zhu
2020-10-09  4:47     ` YiFei Zhu
2020-10-09  5:41       ` Kees Cook
2020-09-30 15:19   ` [PATCH v3 seccomp 3/5] seccomp/cache: Lookup syscall allowlist for fast path YiFei Zhu
2020-09-30 21:32     ` Kees Cook
2020-10-09  0:17       ` YiFei Zhu
2020-10-09  5:35         ` Kees Cook
2020-09-30 15:19   ` [PATCH v3 seccomp 4/5] selftests/seccomp: Compare bitmap vs filter overhead YiFei Zhu
2020-09-30 15:19   ` [PATCH v3 seccomp 5/5] seccomp/cache: Report cache data through /proc/pid/seccomp_cache YiFei Zhu
2020-09-30 22:00     ` Jann Horn
2020-09-30 23:12       ` Kees Cook
2020-10-01 12:06       ` YiFei Zhu
2020-10-01 16:05         ` Jann Horn
2020-10-01 16:18           ` YiFei Zhu
2020-09-30 22:59     ` Kees Cook
2020-09-30 23:08       ` Jann Horn
2020-09-30 23:21         ` Kees Cook
2020-10-09 17:14   ` [PATCH v4 seccomp 0/5] seccomp: Add bitmap cache of constant allow filter results YiFei Zhu
2020-10-09 17:14     ` [PATCH v4 seccomp 1/5] seccomp/cache: Lookup syscall allowlist bitmap for fast path YiFei Zhu
2020-10-09 21:30       ` Jann Horn
2020-10-09 23:18       ` Kees Cook
2020-10-09 17:14     ` [PATCH v4 seccomp 2/5] seccomp/cache: Add "emulator" to check if filter is constant allow YiFei Zhu
2020-10-09 21:30       ` Jann Horn
2020-10-09 22:47         ` Kees Cook
2020-10-09 17:14     ` [PATCH v4 seccomp 3/5] x86: Enable seccomp architecture tracking YiFei Zhu
2020-10-09 17:25       ` Andy Lutomirski
2020-10-09 18:32         ` YiFei Zhu
2020-10-09 20:59           ` Andy Lutomirski
2020-10-09 17:14     ` [PATCH v4 seccomp 4/5] selftests/seccomp: Compare bitmap vs filter overhead YiFei Zhu
2020-10-09 17:14     ` [PATCH v4 seccomp 5/5] seccomp/cache: Report cache data through /proc/pid/seccomp_cache YiFei Zhu
2020-10-09 21:24       ` kernel test robot
2020-10-09 21:45       ` Jann Horn
2020-10-09 23:14       ` Kees Cook
2020-10-10 13:26         ` YiFei Zhu
2020-10-12 22:57           ` Kees Cook
2020-10-13  0:31             ` YiFei Zhu
2020-10-22 20:52               ` YiFei Zhu
2020-10-22 22:32                 ` Kees Cook
2020-10-22 23:40                   ` YiFei Zhu
2020-10-24  2:51                     ` Kees Cook
2020-10-30 12:18                       ` YiFei Zhu
2020-11-03 13:00                         ` YiFei Zhu
2020-11-04  0:29                           ` Kees Cook
2020-11-04 11:40                             ` YiFei Zhu
2020-11-04 18:57                               ` Kees Cook
2020-10-11 15:47     ` [PATCH v5 seccomp 0/5]seccomp: Add bitmap cache of constant allow filter results YiFei Zhu
2020-10-11 15:47       ` [PATCH v5 seccomp 1/5] seccomp/cache: Lookup syscall allowlist bitmap for fast path YiFei Zhu
2020-10-12  6:42         ` Jann Horn
2020-10-11 15:47       ` [PATCH v5 seccomp 2/5] seccomp/cache: Add "emulator" to check if filter is constant allow YiFei Zhu
2020-10-12  6:46         ` Jann Horn
2020-10-11 15:47       ` [PATCH v5 seccomp 3/5] x86: Enable seccomp architecture tracking YiFei Zhu
2020-10-11 15:47       ` [PATCH v5 seccomp 4/5] selftests/seccomp: Compare bitmap vs filter overhead YiFei Zhu
2020-10-11 15:47       ` [PATCH v5 seccomp 5/5] seccomp/cache: Report cache data through /proc/pid/seccomp_cache YiFei Zhu
2020-10-12  6:49         ` Jann Horn
2020-12-17 12:14         ` Geert Uytterhoeven
2020-12-17 18:34           ` YiFei Zhu
2020-12-18 12:35             ` Geert Uytterhoeven
2020-10-27 19:14       ` [PATCH v5 seccomp 0/5]seccomp: Add bitmap cache of constant allow filter results Kees Cook

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