From: Kees Cook <keescook@chromium.org>
To: Jann Horn <jannh@google.com>
Cc: YiFei Zhu <yifeifz2@illinois.edu>,
Paul Moore <paul@paul-moore.com>,
Tom Hromatka <tom.hromatka@oracle.com>,
Christian Brauner <christian.brauner@ubuntu.com>,
Tycho Andersen <tycho@tycho.pizza>,
Andy Lutomirski <luto@amacapital.net>,
Will Drewry <wad@chromium.org>,
Andrea Arcangeli <aarcange@redhat.com>,
Giuseppe Scrivano <gscrivan@redhat.com>,
Tobin Feldman-Fitzthum <tobin@ibm.com>,
Dimitrios Skarlatos <dskarlat@cs.cmu.edu>,
Valentin Rothberg <vrothber@redhat.com>,
Hubertus Franke <frankeh@us.ibm.com>,
Jack Chen <jianyan2@illinois.edu>,
Josep Torrellas <torrella@illinois.edu>,
Tianyin Xu <tyxu@illinois.edu>, bpf <bpf@vger.kernel.org>,
Linux Containers <containers@lists.linux-foundation.org>,
Linux API <linux-api@vger.kernel.org>,
kernel list <linux-kernel@vger.kernel.org>
Subject: Re: [PATCH 4/6] seccomp: Emulate basic filters for constant action results
Date: Thu, 24 Sep 2020 00:46:39 -0700 [thread overview]
Message-ID: <202009240038.864365E@keescook> (raw)
In-Reply-To: <CAG48ez251v19U60GYH4aWE6+C-3PYw5mr_Ax_kxnebqDOBn_+Q@mail.gmail.com>
On Thu, Sep 24, 2020 at 01:47:47AM +0200, Jann Horn wrote:
> On Thu, Sep 24, 2020 at 1:29 AM Kees Cook <keescook@chromium.org> wrote:
> > This emulates absolutely the most basic seccomp filters to figure out
> > if they will always give the same results for a given arch/nr combo.
> >
> > Nearly all seccomp filters are built from the following ops:
> >
> > 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
> >
> > These are now emulated to check for accesses beyond seccomp_data::arch
> > or unknown instructions.
> >
> > Not yet implemented are:
> >
> > BPF_ALU | BPF_AND (generated by libseccomp and Chrome)
>
> BPF_AND is normally only used on syscall arguments, not on the syscall
> number or the architecture, right? And when a syscall argument is
> loaded, we abort execution anyway. So I think there is no need to
> implement those?
Is that right? I can't actually tell what libseccomp is doing with
ALU|AND. It looks like it's using it for building jump lists?
Paul, Tom, under what cases does libseccomp emit ALU|AND into filters?
> > Suggested-by: Jann Horn <jannh@google.com>
> > Link: https://lore.kernel.org/lkml/CAG48ez1p=dR_2ikKq=xVxkoGg0fYpTBpkhJSv1w-6BG=76PAvw@mail.gmail.com/
> > Signed-off-by: Kees Cook <keescook@chromium.org>
> > ---
> > kernel/seccomp.c | 82 ++++++++++++++++++++++++++++++++++++++++++++---
> > net/core/filter.c | 3 +-
> > 2 files changed, 79 insertions(+), 6 deletions(-)
> >
> > diff --git a/kernel/seccomp.c b/kernel/seccomp.c
> > index 111a238bc532..9921f6f39d12 100644
> > --- a/kernel/seccomp.c
> > +++ b/kernel/seccomp.c
> > @@ -610,7 +610,12 @@ static struct seccomp_filter *seccomp_prepare_filter(struct sock_fprog *fprog)
> > {
> > struct seccomp_filter *sfilter;
> > int ret;
> > - const bool save_orig = IS_ENABLED(CONFIG_CHECKPOINT_RESTORE);
> > + const bool save_orig =
> > +#if defined(CONFIG_CHECKPOINT_RESTORE) || defined(SECCOMP_ARCH)
> > + true;
> > +#else
> > + false;
> > +#endif
>
> You could probably write this as something like:
>
> const bool save_orig = IS_ENABLED(CONFIG_CHECKPOINT_RESTORE) ||
> __is_defined(SECCOMP_ARCH);
Ah! Thank you. I went looking for __is_defined() and failed. :)
>
> [...]
> > diff --git a/net/core/filter.c b/net/core/filter.c
> [...]
> > -static void bpf_release_orig_filter(struct bpf_prog *fp)
> > +void bpf_release_orig_filter(struct bpf_prog *fp)
> > {
> > struct sock_fprog_kern *fprog = fp->orig_prog;
> >
> > @@ -1154,6 +1154,7 @@ static void bpf_release_orig_filter(struct bpf_prog *fp)
> > kfree(fprog);
> > }
> > }
> > +EXPORT_SYMBOL_GPL(bpf_release_orig_filter);
>
> If this change really belongs into this patch (which I don't think it
> does), please describe why in the commit message.
Yup, more cruft I failed to remove.
--
Kees Cook
next prev parent reply other threads:[~2020-09-24 7:47 UTC|newest]
Thread overview: 40+ messages / expand[flat|nested] mbox.gz Atom feed top
2020-09-23 23:29 [PATCH v1 0/6] seccomp: Implement constant action bitmaps Kees Cook
2020-09-23 23:29 ` [PATCH 1/6] seccomp: Introduce SECCOMP_PIN_ARCHITECTURE Kees Cook
2020-09-24 0:41 ` Jann Horn
2020-09-24 7:11 ` Kees Cook
2020-09-23 23:29 ` [PATCH 2/6] x86: Enable seccomp architecture tracking Kees Cook
2020-09-24 0:45 ` Jann Horn
2020-09-24 7:12 ` Kees Cook
2020-09-23 23:29 ` [PATCH 3/6] seccomp: Implement constant action bitmaps Kees Cook
2020-09-24 0:25 ` Jann Horn
2020-09-24 7:36 ` Kees Cook
2020-09-24 8:07 ` YiFei Zhu
2020-09-24 8:15 ` Kees Cook
2020-09-24 8:22 ` YiFei Zhu
2020-09-24 12:28 ` Jann Horn
2020-09-24 12:37 ` David Laight
2020-09-24 12:56 ` Jann Horn
[not found] ` <DM6PR11MB271492D0565E91475D949F5DEF390@DM6PR11MB2714.namprd11.prod.outlook.com>
2020-09-24 0:36 ` YiFei Zhu
2020-09-24 7:38 ` Kees Cook
2020-09-24 7:51 ` YiFei Zhu
2020-09-23 23:29 ` [PATCH 4/6] seccomp: Emulate basic filters for constant action results Kees Cook
2020-09-23 23:47 ` Jann Horn
2020-09-24 7:46 ` Kees Cook [this message]
2020-09-24 15:28 ` Paul Moore
2020-09-24 19:52 ` Kees Cook
2020-09-24 20:46 ` Paul Moore
2020-09-24 21:35 ` Kees Cook
2020-09-23 23:29 ` [PATCH 5/6] selftests/seccomp: Compare bitmap vs filter overhead Kees Cook
2020-09-23 23:29 ` [PATCH 6/6] [DEBUG] seccomp: Report bitmap coverage ranges Kees Cook
2020-09-24 13:40 ` [PATCH v1 0/6] seccomp: Implement constant action bitmaps Rasmus Villemoes
2020-09-24 13:58 ` YiFei Zhu
2020-09-25 5:56 ` Rasmus Villemoes
2020-09-25 7:07 ` YiFei Zhu
2020-09-26 18:11 ` YiFei Zhu
2020-09-28 20:04 ` Kees Cook
2020-09-28 20:16 ` YiFei Zhu
2020-09-24 14:05 ` Jann Horn
2020-09-24 18:57 ` Andrea Arcangeli
2020-09-24 19:18 ` Jann Horn
[not found] ` <9dbe8e3bbdad43a1872202ff38c34ca2@DM5PR11MB1692.namprd11.prod.outlook.com>
2020-09-24 19:48 ` Tianyin Xu
2020-09-24 20:00 ` Kees Cook
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