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Date:   Wed, 26 Aug 2020 18:24:01 +1000
From:   Aleksa Sarai <cyphar@cyphar.com>
To:     Shaokun Zhang <zhangshaokun@hisilicon.com>
Cc:     Will Deacon <will@kernel.org>, linux-fsdevel@vger.kernel.org,
        linux-kernel@vger.kernel.org, Mark Rutland <mark.rutland@arm.com>,
        Peter Zijlstra <peterz@infradead.org>,
        Alexander Viro <viro@zeniv.linux.org.uk>,
        Boqun Feng <boqun.feng@gmail.com>,
        Yuqi Jin <jinyuqi@huawei.com>
Subject: Re: [PATCH RESEND] fs: Move @f_count to different cacheline with
 @f_mode
Message-ID: <20200826082401.c6j5fwrbhl7vgmhj@yavin.dot.cyphar.com>
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On 2020-08-26, Shaokun Zhang <zhangshaokun@hisilicon.com> wrote:
> =E5=9C=A8 2020/8/22 0:02, Will Deacon =E5=86=99=E9=81=93:
> >   - This thing is tagged with __randomize_layout, so it doesn't help an=
ybody
> >     using that crazy plugin
>=20
> This patch isolated the @f_count with @f_mode absolutely and we don't car=
e the
> base address of the structure, or I may miss something what you said.

__randomize_layout randomises the order of fields in a structure on each
kernel rebuild (to make attacks against sensitive kernel structures
theoretically harder because the offset of a field is per-build). It is
separate to ASLR or other base-related randomisation. However it depends
on having CONFIG_GCC_PLUGIN_RANDSTRUCT=3Dy and I believe (at least for
distribution kernels) this isn't a widely-used configuration.

--=20
Aleksa Sarai
Senior Software Engineer (Containers)
SUSE Linux GmbH
<https://www.cyphar.com/>

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