From: Daniel Borkmann <daniel@iogearbox.net>
To: Eric Dumazet <eric.dumazet@gmail.com>, alexei.starovoitov@gmail.com
Cc: peterz@infradead.org, netdev@vger.kernel.org,
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: Sat, 30 Nov 2019 10:52:16 +0100 [thread overview]
Message-ID: <10d4c87c-3d53-2dbf-d8c0-8b36863fec60@iogearbox.net> (raw)
In-Reply-To: <ec8264ad-8806-208a-1375-51e7cad1866e@gmail.com>
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/
Thanks,
Daniel
next prev parent reply other threads:[~2019-11-30 9:52 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 [this message]
2019-12-01 17:54 ` Alexei Starovoitov
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
Reply instructions:
You may reply publicly to this message via plain-text email
using any one of the following methods:
* Save the following mbox file, import it into your mail client,
and reply-to-all from there: mbox
Avoid top-posting and favor interleaved quoting:
https://en.wikipedia.org/wiki/Posting_style#Interleaved_style
* Reply using the --to, --cc, and --in-reply-to
switches of git-send-email(1):
git send-email \
--in-reply-to=10d4c87c-3d53-2dbf-d8c0-8b36863fec60@iogearbox.net \
--to=daniel@iogearbox.net \
--cc=alexei.starovoitov@gmail.com \
--cc=bpf@vger.kernel.org \
--cc=eric.dumazet@gmail.com \
--cc=hpa@zytor.com \
--cc=netdev@vger.kernel.org \
--cc=peterz@infradead.org \
/path/to/YOUR_REPLY
https://kernel.org/pub/software/scm/git/docs/git-send-email.html
* If your mail client supports setting the In-Reply-To header
via mailto: links, try the mailto: link
Be sure your reply has a Subject: header at the top and a blank line
before the message body.
This is a public inbox, see mirroring instructions
for how to clone and mirror all data and code used for this inbox;
as well as URLs for NNTP newsgroup(s).