linux-kernel - Re: [PATCH RESEND] fs: Move @f_count to different cacheline with @f

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Date:   Thu, 27 Aug 2020 16:27:34 +0800
From:   Shaokun Zhang <zhangshaokun@...ilicon.com>
To:     Aleksa Sarai <cyphar@...har.com>
CC:     Will Deacon <will@...nel.org>, <linux-fsdevel@...r.kernel.org>,
        <linux-kernel@...r.kernel.org>,
        Mark Rutland <mark.rutland@....com>,
        "Peter Zijlstra" <peterz@...radead.org>,
        Alexander Viro <viro@...iv.linux.org.uk>,
        Boqun Feng <boqun.feng@...il.com>,
        Yuqi Jin <jinyuqi@...wei.com>
Subject: Re: [PATCH RESEND] fs: Move @f_count to different cacheline with
 @f_mode

Hi Aleksa,

在 2020/8/26 16:24, Aleksa Sarai 写道:
> On 2020-08-26, Shaokun Zhang <zhangshaokun@...ilicon.com> wrote:
>> 在 2020/8/22 0:02, Will Deacon 写道:
>>>   - This thing is tagged with __randomize_layout, so it doesn't help anybody
>>>     using that crazy plugin
>>
>> This patch isolated the @f_count with @f_mode absolutely and we don't care 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

My bad, I missed Will's comments for my poor understanding on it.

> separate to ASLR or other base-related randomisation. However it depends
> on having CONFIG_GCC_PLUGIN_RANDSTRUCT=y and I believe (at least for
> distribution kernels) this isn't a widely-used configuration.

Thanks for more explanations about it, in our test, this config is also
disabled. If having CONFIG_GCC_PLUGIN_RANDSTRUCT=y, it seems this patch
will lose its value.
If it isn't widely-used for this config, hopefully we can do something on
the scene.

Thanks,
Shaokun

>