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From:   Kees Cook <keescook@chromium.org>
Date:   Tue, 13 Feb 2018 13:43:49 -0800
Message-ID: <CAGXu5j+zOCLerneUt2b-tvyLLg7fEbr9B0YYow-4DH6oV-nnCw@mail.gmail.com>
Subject: Re: [kernel-hardening] [PATCH 4/6] Protectable Memory
To:     Laura Abbott <labbott@redhat.com>
Cc:     Jann Horn <jannh@google.com>, Igor Stoppa <igor.stoppa@huawei.com>,
        Boris Lukashev <blukashev@sempervictus.com>,
        Christopher Lameter <cl@linux.com>,
        Matthew Wilcox <willy@infradead.org>,
        Jerome Glisse <jglisse@redhat.com>,
        Michal Hocko <mhocko@kernel.org>,
        Christoph Hellwig <hch@infradead.org>,
        linux-security-module <linux-security-module@vger.kernel.org>,
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On Tue, Feb 13, 2018 at 8:09 AM, Laura Abbott <labbott@redhat.com> wrote:
> No, arm64 doesn't fixup the aliases, mostly because arm64 uses larger
> page sizes which can't be broken down at runtime. CONFIG_PAGE_POISONING
> does use 4K pages which could be adjusted at runtime. So yes, you are
> right we would have physmap exposure on arm64 as well.

Errr, so that means even modules and kernel code are writable via the
arm64 physmap? That seems extraordinarily bad. :(

-Kees

-- 
Kees Cook
Pixel Security