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 v4 seccomp 2/5] seccomp/cache: Add "emulator" to check if filter is constant allow
Date: Fri, 9 Oct 2020 15:47:07 -0700 [thread overview]
Message-ID: <202010091545.962A2F5@keescook> (raw)
In-Reply-To: <CAG48ez1eUfjNPVKeYbk28On9WOaDBysR-=7sYDM-Q=nCzwXcDA@mail.gmail.com>
On Fri, Oct 09, 2020 at 11:30:18PM +0200, Jann Horn wrote:
> On Fri, Oct 9, 2020 at 7:15 PM YiFei Zhu <zhuyifei1999@gmail.com> wrote:
> >
> > From: YiFei Zhu <yifeifz2@illinois.edu>
> >
> > SECCOMP_CACHE 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.
> >
> > In order to build this bitmap at filter attach time, each filter is
> > emulated for every syscall (under each possible architecture), and
> > checked for any accesses of struct seccomp_data that are not the "arch"
> > nor "nr" (syscall) members. If only "arch" and "nr" are examined, and
> > the program returns allow, then we can be sure that the filter must
> > return allow independent from syscall arguments.
> >
> > Nearly all seccomp filters are built from these cBPF instructions:
> >
> > BPF_LD | BPF_W | BPF_ABS
> > BPF_JMP | BPF_JEQ | BPF_K
> > BPF_JMP | BPF_JGE | BPF_K
> > BPF_JMP | BPF_JGT | BPF_K
> > BPF_JMP | BPF_JSET | BPF_K
> > BPF_JMP | BPF_JA
> > BPF_RET | BPF_K
> > BPF_ALU | BPF_AND | BPF_K
> >
> > Each of these instructions 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/
> [...]
> > @@ -682,6 +693,150 @@ seccomp_prepare_user_filter(const char __user *user_filter)
> > return filter;
> > }
> >
> > +#ifdef SECCOMP_ARCH_NATIVE
> > +/**
> > + * seccomp_is_const_allow - check if filter is constant allow with given data
> > + * @fprog: The BPF programs
> > + * @sd: The seccomp data to check against, only syscall number are arch
> > + * number are considered constant.
>
> nit: s/syscall number are arch number/syscall number and arch number/
>
> > + */
> > +static bool seccomp_is_const_allow(struct sock_fprog_kern *fprog,
> > + struct seccomp_data *sd)
> > +{
> > + unsigned int insns;
> > + unsigned int reg_value = 0;
> > + unsigned int pc;
> > + bool op_res;
> > +
> > + if (WARN_ON_ONCE(!fprog))
> > + return false;
> > +
> > + insns = bpf_classic_proglen(fprog);
>
> bpf_classic_proglen() is defined as:
>
> #define bpf_classic_proglen(fprog) (fprog->len * sizeof(fprog->filter[0]))
>
> so this is wrong - what you want is the number of instructions in the
> program, what you actually have is the size of the program in bytes.
> Please instead check for `pc < fprog->len` in the loop condition.
Oh yes, good catch. I had this wrong in my v1.
--
Kees Cook
next prev parent reply other threads:[~2020-10-09 22:48 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
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 [this message]
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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