linux-kernel - Re: [PATCH bpf-next] bpf: Make trampolines W^X

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Message-ID: <20200107185532.4zax5j5ln456u7rj@ast-mbp>
Date:   Tue, 7 Jan 2020 10:55:33 -0800
From:   Alexei Starovoitov <alexei.starovoitov@...il.com>
To:     Peter Zijlstra <peterz@...radead.org>
Cc:     Andy Lutomirski <luto@...capital.net>,
        Justin Capella <justincapella@...il.com>,
        KP Singh <kpsingh@...omium.org>,
        Rick Edgecombe <rick.p.edgecombe@...el.com>,
        linux-kernel@...r.kernel.org, bpf@...r.kernel.org, x86@...nel.org,
        linux-security-module@...r.kernel.org,
        Kees Cook <keescook@...omium.org>,
        "David S. Miller" <davem@...emloft.net>,
        Alexey Kuznetsov <kuznet@....inr.ac.ru>,
        Hideaki YOSHIFUJI <yoshfuji@...ux-ipv6.org>,
        Alexei Starovoitov <ast@...nel.org>,
        Daniel Borkmann <daniel@...earbox.net>,
        Martin KaFai Lau <kafai@...com>,
        Song Liu <songliubraving@...com>, Yonghong Song <yhs@...com>,
        Andrii Nakryiko <andriin@...com>,
        Thomas Garnier <thgarnie@...omium.org>,
        Florent Revest <revest@...omium.org>,
        Brendan Jackman <jackmanb@...omium.org>,
        Jann Horn <jannh@...gle.com>,
        Matthew Garrett <mjg59@...gle.com>,
        Michael Halcrow <mhalcrow@...gle.com>
Subject: Re: [PATCH bpf-next] bpf: Make trampolines W^X

On Tue, Jan 07, 2020 at 10:11:32AM +0100, Peter Zijlstra wrote:
> On Mon, Jan 06, 2020 at 02:13:18PM -0800, Alexei Starovoitov wrote:
> > On Sun, Jan 05, 2020 at 10:33:54AM +0900, Andy Lutomirski wrote:
> > > 
> > > >> On Jan 4, 2020, at 8:03 PM, Justin Capella <justincapella@...il.com> wrote:
> > > > 
> > > > I'm rather ignorant about this topic but it would make sense to check prior to making executable from a security standpoint wouldn't it? (In support of the (set_memory_ro + set_memory_x)
> > > > 
> > > 
> > > Maybe, depends if it’s structured in a way that’s actually helpful from a security perspective.
> > > 
> > > It doesn’t help that set_memory_x and friends are not optimized at all. These functions are very, very, very slow and adversely affect all CPUs.
> > 
> > That was one of the reason it wasn't done in the first.
> > Also ftrace trampoline break w^x as well.
> 
> Didn't I fix that?

yes. in the tip. many months ago. that's why up-thread I was saying that I'm
waiting for all text_poke[_bp] patches to land upstream and do the same thing
for bpf trampoline and bpf dispatcher (which has the same issue).