linux-kernel - Re: [PATCH 1/2] x86/bugs: Check VERW mitigations for consistency

lists.openwall.net		lists / announce owl-users owl-dev john-users john-dev passwdqc-users yescrypt popa3d-users / oss-security kernel-hardening musl sabotage tlsify passwords / crypt-dev xvendor / Bugtraq Full-Disclosure linux-kernel linux-netdev linux-ext4 linux-hardening linux-cve-announce PHC
Open Source and information security mailing list archives

Hash Suite: Windows password security audit tool. GUI, reports in PDF.

[<prev] [next>] [<thread-prev] [thread-next>] [day] [month] [year] [list]

Message-ID: <9ef41b96-8b96-441e-b053-4d7c7d9aa74a@linux.intel.com>
Date: Tue, 29 Oct 2024 07:35:41 -0700
From: Daniel Sneddon <daniel.sneddon@...ux.intel.com>
To: Borislav Petkov <bp@...en8.de>
Cc: Jonathan Corbet <corbet@....net>, Thomas Gleixner <tglx@...utronix.de>,
 Peter Zijlstra <peterz@...radead.org>, Josh Poimboeuf <jpoimboe@...nel.org>,
 Ingo Molnar <mingo@...hat.com>, Dave Hansen <dave.hansen@...ux.intel.com>,
 x86@...nel.org, hpa@...or.com, linux-doc@...r.kernel.org,
 linux-kernel@...r.kernel.org, pawan.kumar.gupta@...ux.intel.com
Subject: Re: [PATCH 1/2] x86/bugs: Check VERW mitigations for consistency

On 10/29/24 04:39, Borislav Petkov wrote:
> On Mon, Oct 28, 2024 at 04:50:34PM -0700, Daniel Sneddon wrote:
>> There are currently 4 mitigations that use VERW: MDS, TAA,
>> MMIO Stale Data, and Register File Data Sampling. Because
>> all 4 use the same mitigation path, if any one of them is
>> enabled, they're all enabled. Normally, this is what is
>> wanted. However, if a user wants to disable the mitigation,
>> this can cause problems. If the user misses disabling even
>> one of these mitigations, then none of them will be
>> disabled. This can cause confusion as the user expects to
>> regain the performance lost to the mitigation but isn't
>> seeing any improvement. Since there are already 4 knobs for
>> controlling it, adding a 5th knob that controls all 4
>> mitigations together would just overcomplicate things.
>> Instead, let the user know their mitigations are out of sync
>> when at least one of these mitigations is disabled but not
>> all 4.
> 
> Please split this commit message into smaller chunks for better readability.
> For example:
> 
>     There are currently 4 mitigations that use VERW: MDS, TAA, MMIO Stale Data,
>     and Register File Data Sampling. Because all 4 use the same mitigation path,
>     if any one of them is enabled, they're all enabled.
>     
>     Normally, this is what is wanted. However, if a user wants to disable the
>     mitigation, this can cause problems. If the user misses disabling even one of
>     these mitigations, then none of them will be disabled.
>     
>     This can cause confusion as the user expects to regain the performance lost to
>     the mitigation but isn't seeing any improvement. Since there are already
>     4 knobs for controlling it, adding a 5th knob that controls all 4 mitigations
>     together would just overcomplicate things.
>     
>     Instead, let the user know their mitigations are out of sync when at least one
>     of these mitigations is disabled but not all 4.
> 
> Thx.
> 

Will do.