netdev - Re: [PATCH] ebpf: verify the output of the JIT

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Date:   Tue, 4 Apr 2017 21:45:36 -0600
From:   Tycho Andersen <tycho@...ker.com>
To:     Kees Cook <keescook@...omium.org>
Cc:     Daniel Borkmann <daniel@...earbox.net>,
        Alexei Starovoitov <ast@...nel.org>,
        LKML <linux-kernel@...r.kernel.org>,
        Network Development <netdev@...r.kernel.org>,
        "kernel-hardening@...ts.openwall.com" 
        <kernel-hardening@...ts.openwall.com>,
        Mickaël Salaün <mic@...ikod.net>
Subject: Re: [PATCH] ebpf: verify the output of the JIT

Hi Kees,

On Tue, Apr 04, 2017 at 03:17:57PM -0700, Kees Cook wrote:
> On Tue, Apr 4, 2017 at 3:08 PM, Tycho Andersen <tycho@...ker.com> wrote:
> > The goal of this patch is to protect the JIT against an attacker with a
> > write-in-memory primitive. The JIT allocates a buffer which will eventually
> > be marked +x, so we need to make sure that what was written to this buffer
> > is what was intended.
> >
> > We acheive this by building a hash of the instruction buffer as
> > instructions are emittted and then comparing that to a hash at the end of
> > the JIT compile after the buffer has been marked read-only.
> >
> > Signed-off-by: Tycho Andersen <tycho@...ker.com>
> > CC: Daniel Borkmann <daniel@...earbox.net>
> > CC: Alexei Starovoitov <ast@...nel.org>
> > CC: Kees Cook <keescook@...omium.org>
> > CC: Mickaël Salaün <mic@...ikod.net>
> 
> Cool! This closes the race condition on producing the JIT vs going
> read-only. I wonder if it might be possible to make this a more
> generic interface to the BPF which would be allocate the hash, provide
> the update callback during emit, and then do the hash check itself at
> the end of bpf_jit_binary_lock_ro()?

Yes, probably so. I can look into that for the next version.

Tycho