linux-kernel - Re: [RFC][PATCH 06/17] x86/cpu: Add SRSO untrain to retbleed=

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Date:   Thu, 10 Aug 2023 12:10:03 -0400
From:   Josh Poimboeuf <jpoimboe@...nel.org>
To:     Borislav Petkov <bp@...en8.de>
Cc:     Peter Zijlstra <peterz@...radead.org>, x86@...nel.org,
        linux-kernel@...r.kernel.org, David.Kaplan@....com,
        Andrew.Cooper3@...rix.com, gregkh@...uxfoundation.org
Subject: Re: [RFC][PATCH 06/17] x86/cpu: Add SRSO untrain to retbleed=

On Thu, Aug 10, 2023 at 05:44:04PM +0200, Borislav Petkov wrote:
> On Wed, Aug 09, 2023 at 09:12:24AM +0200, Peter Zijlstra wrote:
> > Since it is now readily apparent that the two SRSO
> > untrain_ret+return_thunk variants are exactly the same mechanism as
> > the existing (retbleed) zen untrain_ret+return_thunk, add them to the
> > existing retbleed options.
> 
> Except that Zen3/4 are not affected by retbleed, according to my current
> state of information.
> 
> I don't like this lumping together of the issues even if their
> mitigations are more or less similar.

I tend to agree that SRSO is a new issue and should have its own sysfs
and cmdline options (though a separate CONFIG option is overkill IMO).

The mitigations are unfortunately intertwined, but we've been in that
situation several times before (e.g., spectre_v2 + intel retbleed).

-- 
Josh