linux-kernel - Re: [PATCH RFC 3/4] x86/pti: don't mark the user PGD with _PAGE

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Message-ID: <CA+55aFyCGw3sq4s_5qtg5rJGU_F6efWanOutYo4E-eiZSs05nQ@mail.gmail.com>
Date:   Mon, 8 Jan 2018 10:35:32 -0800
From:   Linus Torvalds <torvalds@...ux-foundation.org>
To:     Alan Cox <gnomes@...rguk.ukuu.org.uk>
Cc:     Ingo Molnar <mingo@...nel.org>,
        Dave Hansen <dave.hansen@...el.com>,
        Thomas Gleixner <tglx@...utronix.de>, Willy Tarreau <w@....eu>,
        Linux Kernel Mailing List <linux-kernel@...r.kernel.org>,
        "the arch/x86 maintainers" <x86@...nel.org>
Subject: Re: [PATCH RFC 3/4] x86/pti: don't mark the user PGD with _PAGE_NX.

On Mon, Jan 8, 2018 at 10:25 AM, Alan Cox <gnomes@...rguk.ukuu.org.uk> wrote:
>
> I still think cgroups are the best model for this. In particular it
> naturally fits things like containers, or network facing apps that fork
> helpers.
>
> Secondly when you are looking at barrier semantics between client/client
> a cgroup is much more natural as a way to group processes together who
> don't need to be protected from each other as they are trusting each
> other. (Or we could just harcode this based upon ptraceability ?)

I agree that cgroups would be fairly natural, but I do think we could
look at things like simply trusted users too ("running as root? Yeah,
we're not going to try to protect the kernel from you") and/or trusted
binaries.

But all of those things are likely things that can easily be
determined at execve() time.

                      Linus