linux-kernel - Re: [PATCH v2] hugetlb: clean up potential spectre issue warnings

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Date:   Thu, 24 Feb 2022 10:31:40 +0100
From:   Michal Hocko <mhocko@...e.com>
To:     Mike Kravetz <mike.kravetz@...cle.com>
Cc:     linux-mm@...ck.org, linux-kernel@...r.kernel.org,
        Baolin Wang <baolin.wang@...ux.alibaba.com>,
        Zhenguo Yao <yaozhenguo1@...il.com>,
        Liu Yuntao <liuyuntao10@...wei.com>,
        Dan Carpenter <dan.carpenter@...cle.com>,
        Andrew Morton <akpm@...ux-foundation.org>
Subject: Re: [PATCH v2] hugetlb: clean up potential spectre issue warnings

On Wed 23-02-22 10:36:55, Mike Kravetz wrote:
> On 2/23/22 00:33, Michal Hocko wrote:
> > On Tue 22-02-22 13:53:56, Mike Kravetz wrote:
> >> On 2/21/22 23:47, Michal Hocko wrote:
> >> How about adding this note to the commit message?
> >>
> >> Note: these routines take a user specified value used as an index ONCE
> >> during the boot process.  As a result, they can not be used as a general
> >> method of exploitation.  Code changes are being made to eliminate warnings.
> > 
> > This would help but the question whether the change is worth remains.
> > Does this change have any other advantage than silencing the warning?
> > 
> 
> Silencing the warnings was the primary motivation for the change.  If Dan
> has a plan to change smatch so that they are silenced for __init functions,
> then it would be better to not make the changes to use array_index_nospec.
> 
> While making the changes, I shuffled the code a little and did not immediately
> notice that it also 'fixes' an overflow/truncation issue when assigning an
> unsigned long to int as addressed in [1].  We should probably make this change
> whether or not we use array_index_nospec to silence warnings.
> 
> [1] https://lore.kernel.org/linux-mm/20220209134018.8242-1-liuyuntao10@huawei.com/

Yeah, this makes sense to me.
-- 
Michal Hocko
SUSE Labs