linux-kernel - Re: [PATCH bpf] bpf: add bpf_jit_limit knob to restrict unpriv allocations

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Message-ID: <20181026001711.w55n5au2vx3sepmb@ast-mbp>
Date:   Thu, 25 Oct 2018 17:17:13 -0700
From:   Alexei Starovoitov <alexei.starovoitov@...il.com>
To:     Daniel Borkmann <daniel@...earbox.net>
Cc:     ast@...nel.org, rick.p.edgecombe@...el.com, eric.dumazet@...il.com,
        jannh@...gle.com, keescook@...omium.org,
        linux-kernel@...r.kernel.org, netdev@...r.kernel.org
Subject: Re: [PATCH bpf] bpf: add bpf_jit_limit knob to restrict unpriv
 allocations

On Tue, Oct 23, 2018 at 01:11:04AM +0200, Daniel Borkmann wrote:
> Rick reported that the BPF JIT could potentially fill the entire module
> space with BPF programs from unprivileged users which would prevent later
> attempts to load normal kernel modules or privileged BPF programs, for
> example. If JIT was enabled but unsuccessful to generate the image, then
> before commit 290af86629b2 ("bpf: introduce BPF_JIT_ALWAYS_ON config")
> we would always fall back to the BPF interpreter. Nowadays in the case
> where the CONFIG_BPF_JIT_ALWAYS_ON could be set, then the load will abort
> with a failure since the BPF interpreter was compiled out.
> 
> Add a global limit and enforce it for unprivileged users such that in case
> of BPF interpreter compiled out we fail once the limit has been reached
> or we fall back to BPF interpreter earlier w/o using module mem if latter
> was compiled in. In a next step, fair share among unprivileged users can
> be resolved in particular for the case where we would fail hard once limit
> is reached.
> 
> Fixes: 290af86629b2 ("bpf: introduce BPF_JIT_ALWAYS_ON config")
> Fixes: 0a14842f5a3c ("net: filter: Just In Time compiler for x86-64")
> Co-Developed-by: Rick Edgecombe <rick.p.edgecombe@...el.com>
> Signed-off-by: Daniel Borkmann <daniel@...earbox.net>
> Acked-by: Alexei Starovoitov <ast@...nel.org>
> Cc: Eric Dumazet <eric.dumazet@...il.com>
> Cc: Jann Horn <jannh@...gle.com>
> Cc: Kees Cook <keescook@...omium.org>
> Cc: LKML <linux-kernel@...r.kernel.org>
> ---
>  Hi Rick, I've reworked the original patch into something much simpler
>  which is only focussing on the actual main issue we want to resolve right
>  now as a first step to make some forward progress, that is, limiting usage
>  on the JIT for unprivileged users. Tested the below on x86 and arm64.
>  (Trimmed down massive Cc list as well a bit and Cc'ed people related to
>  commits referenced and netdev where BPF patches are usually discussed.)
>  Thanks a lot!

Applied to bpf tree. Thanks Daniel.