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From:   Andy Lutomirski <luto@kernel.org>
Date:   Tue, 13 Nov 2018 10:36:45 -0800
Message-ID: <CALCETrV0sPgf4ZgG1joF_5hM-ycPsWM9DWGO=diQ_LQKin4VuA@mail.gmail.com>
Subject: Re: [PATCH 10/17] prmem: documentation
To:     Igor Stoppa <igor.stoppa@huawei.com>
Cc:     Nadav Amit <nadav.amit@gmail.com>,
        Igor Stoppa <igor.stoppa@gmail.com>,
        Kees Cook <keescook@chromium.org>,
        Peter Zijlstra <peterz@infradead.org>,
        Mimi Zohar <zohar@linux.vnet.ibm.com>,
        Matthew Wilcox <willy@infradead.org>,
        Dave Chinner <david@fromorbit.com>,
        James Morris <jmorris@namei.org>,
        Michal Hocko <mhocko@kernel.org>,
        Kernel Hardening <kernel-hardening@lists.openwall.com>,
        linux-integrity <linux-integrity@vger.kernel.org>,
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        Dave Hansen <dave.hansen@linux.intel.com>,
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On Tue, Nov 13, 2018 at 10:33 AM Igor Stoppa <igor.stoppa@huawei.com> wrote:
>
> I forgot one sentence :-(
>
> On 13/11/2018 20:31, Igor Stoppa wrote:
> > On 13/11/2018 19:47, Andy Lutomirski wrote:
> >
> >> For general rare-writish stuff, I don't think we want IRQs running
> >> with them mapped anywhere for write.  For AVC and IMA, I'm less sure.
> >
> > Why would these be less sensitive?
> >
> > But I see a big difference between my initial implementation and this one.
> >
> > In my case, by using a shared mapping, visible to all cores, freezing
> > the core that is performing the write would have exposed the writable
> > mapping to a potential attack run from another core.
> >
> > If the mapping is private to the core performing the write, even if it
> > is frozen, it's much harder to figure out what it had mapped and where,
> > from another core.
> >
> > To access that mapping, the attack should be performed from the ISR, I
> > think.
>
> Unless the secondary mapping is also available to other cores, through
> the shared mm_struct ?
>

I don't think this matters much.  The other cores will only be able to
use that mapping when they're doing a rare write.