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

From: Alexei Starovoitov
Date: Thu Oct 25 2018 - 20:17:20 EST

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@xxxxxxxxx>
> Signed-off-by: Daniel Borkmann <daniel@xxxxxxxxxxxxx>
> Acked-by: Alexei Starovoitov <ast@xxxxxxxxxx>
> Cc: Eric Dumazet <eric.dumazet@xxxxxxxxx>
> Cc: Jann Horn <jannh@xxxxxxxxxx>
> Cc: Kees Cook <keescook@xxxxxxxxxxxx>
> Cc: LKML <linux-kernel@xxxxxxxxxxxxxxx>
> ---
> 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.