Received-SPF: pass (google.com: domain of linux-kernel-owner@vger.kernel.org designates 23.128.96.18 as permitted sender) client-ip=23.128.96.18;
Subject: Re: [PATCH RESEND] fs: Move @f_count to different cacheline with
 @f_mode
To:     Aleksa Sarai <cyphar@cyphar.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>
References: <1592987548-8653-1-git-send-email-zhangshaokun@hisilicon.com>
 <20200821160252.GC21517@willie-the-truck>
 <a75e514c-7e2d-54ed-45d4-327b2a514e67@hisilicon.com>
 <20200826082401.c6j5fwrbhl7vgmhj@yavin.dot.cyphar.com>
From:   Shaokun Zhang <zhangshaokun@hisilicon.com>
Message-ID: <803a5202-6240-b062-b1d9-2aed0e11ebad@hisilicon.com>
Date:   Thu, 27 Aug 2020 16:27:34 +0800
User-Agent: Mozilla/5.0 (Windows NT 10.0; WOW64; rv:68.0) Gecko/20100101
 Thunderbird/68.8.1
MIME-Version: 1.0
In-Reply-To: <20200826082401.c6j5fwrbhl7vgmhj@yavin.dot.cyphar.com>
Content-Type: text/plain; charset="utf-8"
Content-Transfer-Encoding: 8bit
Sender: linux-kernel-owner@vger.kernel.org
Precedence: bulk

Hi Aleksa,

在 2020/8/26 16:24, Aleksa Sarai 写道:
> On 2020-08-26, Shaokun Zhang <zhangshaokun@hisilicon.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

>