linux-kernel - Re: [PATCH bpf-next v1 06/13] bpf: lsm: Init Hooks and create files in securityfs

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Date:   Sat, 4 Jan 2020 00:53:13 +0100
From:   KP Singh <kpsingh@...omium.org>
To:     Kees Cook <keescook@...omium.org>
Cc:     Andrii Nakryiko <andrii.nakryiko@...il.com>,
        open list <linux-kernel@...r.kernel.org>,
        bpf <bpf@...r.kernel.org>, linux-security-module@...r.kernel.org,
        Alexei Starovoitov <ast@...nel.org>,
        Daniel Borkmann <daniel@...earbox.net>,
        James Morris <jmorris@...ei.org>,
        Thomas Garnier <thgarnie@...omium.org>,
        Michael Halcrow <mhalcrow@...gle.com>,
        Paul Turner <pjt@...gle.com>,
        Brendan Gregg <brendan.d.gregg@...il.com>,
        Jann Horn <jannh@...gle.com>,
        Matthew Garrett <mjg59@...gle.com>,
        Christian Brauner <christian@...uner.io>,
        Mickaël Salaün <mic@...ikod.net>,
        Florent Revest <revest@...omium.org>,
        Brendan Jackman <jackmanb@...omium.org>,
        Martin KaFai Lau <kafai@...com>,
        Song Liu <songliubraving@...com>, Yonghong Song <yhs@...com>,
        "Serge E. Hallyn" <serge@...lyn.com>,
        Mauro Carvalho Chehab <mchehab+samsung@...nel.org>,
        "David S. Miller" <davem@...emloft.net>,
        Greg Kroah-Hartman <gregkh@...uxfoundation.org>,
        Nicolas Ferre <nicolas.ferre@...rochip.com>,
        Stanislav Fomichev <sdf@...gle.com>,
        Quentin Monnet <quentin.monnet@...ronome.com>,
        Andrey Ignatov <rdna@...com>, Joe Stringer <joe@...d.net.nz>
Subject: Re: [PATCH bpf-next v1 06/13] bpf: lsm: Init Hooks and create files
 in securityfs

On 30-Dez 11:20, Kees Cook wrote:
> On Mon, Dec 30, 2019 at 04:37:11PM +0100, KP Singh wrote:
> > On 23-Dec 22:28, Andrii Nakryiko wrote:
> > > On Fri, Dec 20, 2019 at 7:43 AM KP Singh <kpsingh@...omium.org> wrote:
> > > [...]
> > 
> > Good catch! You're right. These macros will not be there in v2 as
> > we move to using trampolines based callbacks.
> 
> Speaking of which -- is the BPF trampoline code correctly designed to be
> W^X?

Thanks for pointing this out!

I don't think this is the case as of now.

The dispatcher logic and the tracing programs allocate one page where
one half of it is used for the active trampoline and the other half is
used as a staging area for a future replacement. I sent a patch as an
attempt to fix this:

   https://lore.kernel.org/bpf/20200103234725.22846-1-kpsingh@chromium.org/T/#u

- KP

> 
> -- 
> Kees Cook