From: Alexei Starovoitov <alexei.starovoitov@gmail.com>
To: Daniel Borkmann <daniel@iogearbox.net>
Cc: Eric Dumazet <eric.dumazet@gmail.com>,
Peter Zijlstra <peterz@infradead.org>,
Network Development <netdev@vger.kernel.org>,
bpf <bpf@vger.kernel.org>, "H. Peter Anvin" <hpa@zytor.com>
Subject: Re: [PATCH bpf] bpf: avoid setting bpf insns pages read-only when prog is jited
Date: Sun, 1 Dec 2019 09:54:01 -0800 [thread overview]
Message-ID: <CAADnVQ+8nOiTXJYKV+36Yg8+bkxAJVW5LdcjqLVeEiLRyNLCDA@mail.gmail.com> (raw)
In-Reply-To: <10d4c87c-3d53-2dbf-d8c0-8b36863fec60@iogearbox.net>
On Sat, Nov 30, 2019 at 1:52 AM Daniel Borkmann <daniel@iogearbox.net> wrote:
>
> On 11/30/19 2:37 AM, Eric Dumazet wrote:
> > On 11/29/19 2:29 PM, Daniel Borkmann wrote:
> >> For the case where the interpreter is compiled out or when the prog is jited
> >> it is completely unnecessary to set the BPF insn pages as read-only. In fact,
> >> on frequent churn of BPF programs, it could lead to performance degradation of
> >> the system over time since it would break the direct map down to 4k pages when
> >> calling set_memory_ro() for the insn buffer on x86-64 / arm64 and there is no
> >> reverse operation. Thus, avoid breaking up large pages for data maps, and only
> >> limit this to the module range used by the JIT where it is necessary to set
> >> the image read-only and executable.
> >
> > Interesting... But why the non JIT case would need RO protection ?
>
> It was done for interpreter around 5 years ago mainly due to concerns from security
> folks that the BPF insn image could get corrupted (through some other bug in the
> kernel) in post-verifier stage by an attacker and then there's nothing really that
> would provide any sort of protection guarantees; pretty much the same reasons why
> e.g. modules are set to read-only in the kernel.
>
> > Do you have any performance measures to share ?
>
> No numbers, and I'm also not aware of any reports from users, but it was recently
> brought to our attention from mm folks during discussion of a different set:
>
> https://lore.kernel.org/lkml/1572171452-7958-2-git-send-email-rppt@kernel.org/T/
Applied. Thanks
next prev parent reply other threads:[~2019-12-01 17:54 UTC|newest]
Thread overview: 10+ messages / expand[flat|nested] mbox.gz Atom feed top
2019-11-29 22:29 [PATCH bpf] bpf: avoid setting bpf insns pages read-only when prog is jited Daniel Borkmann
2019-11-30 1:37 ` Eric Dumazet
2019-11-30 9:52 ` Daniel Borkmann
2019-12-01 17:54 ` Alexei Starovoitov [this message]
2019-12-02 2:49 ` Eric Dumazet
2019-12-02 3:44 ` hpa
2019-12-02 8:30 ` Peter Zijlstra
2019-12-02 9:17 ` Daniel Borkmann
2019-12-02 16:19 ` Alexei Starovoitov
2019-12-02 20:09 ` Daniel Borkmann
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