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From: Alexei Starovoitov <alexei.starovoitov@gmail.com>
To: Daniel Borkmann <daniel@iogearbox.net>
Cc: Peter Zijlstra <peterz@infradead.org>,
	Eric Dumazet <eric.dumazet@gmail.com>,
	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: Mon, 2 Dec 2019 08:19:45 -0800	[thread overview]
Message-ID: <CAADnVQJEqVmwAJ2V9NB+0Udwg5H9KJfCSjuSpARAGHLPuhnA=w@mail.gmail.com> (raw)
In-Reply-To: <20191202091716.GA30232@localhost.localdomain>

On Mon, Dec 2, 2019 at 1:17 AM Daniel Borkmann <daniel@iogearbox.net> wrote:
>
> On Mon, Dec 02, 2019 at 09:30:06AM +0100, Peter Zijlstra wrote:
> > On Sun, Dec 01, 2019 at 06:49:32PM -0800, Eric Dumazet wrote:
> >
> > > Thanks for the link !
> > >
> > > Having RO protection as a debug feature would be useful.
> > >
> > > I believe we have CONFIG_STRICT_MODULE_RWX (and CONFIG_STRICT_KERNEL_RWX) for that already.
> > >
> > > Or are we saying we also want to get rid of them ?
> >
> > No, in fact I'm working on making that stronger. We currently still have
> > a few cases that violate the W^X rule.
> >
> > The thing is, when the BPF stuff is JIT'ed, the actual BPF instruction
> > page is not actually executed at all, so making it RO serves no purpose,
> > other than to fragment the direct map.
>
> Yes exactly, in that case it is only used for dumping the BPF insns back
> to user space and therefore no need at all to set it RO. (The JITed image
> however *is* set as RO. - Perhaps there was some confusion given your
> earlier question.)

May be we should also flip the default to net.core.bpf_jit_enable=1
for x86-64 ? and may be arm64 ? These two JITs are well tested
and maintained.

  reply	other threads:[~2019-12-02 16:20 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
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 [this message]
2019-12-02 20:09             ` Daniel Borkmann

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