linux-kernel - RE: [PATCH v4 17/36] Documentation/x86: Document the new attack vector controls

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Message-ID:
 <LV3PR12MB9265B84234C24D42E7CB42EC94B22@LV3PR12MB9265.namprd12.prod.outlook.com>
Date: Tue, 15 Apr 2025 14:59:32 +0000
From: "Kaplan, David" <David.Kaplan@....com>
To: Josh Poimboeuf <jpoimboe@...nel.org>
CC: Thomas Gleixner <tglx@...utronix.de>, Borislav Petkov <bp@...en8.de>,
	Peter Zijlstra <peterz@...radead.org>, Pawan Gupta
	<pawan.kumar.gupta@...ux.intel.com>, Ingo Molnar <mingo@...hat.com>, Dave
 Hansen <dave.hansen@...ux.intel.com>, "x86@...nel.org" <x86@...nel.org>, "H .
 Peter Anvin" <hpa@...or.com>, "linux-kernel@...r.kernel.org"
	<linux-kernel@...r.kernel.org>, Brendan Jackman <jackmanb@...gle.com>, Derek
 Manwaring <derekmn@...zon.com>
Subject: RE: [PATCH v4 17/36] Documentation/x86: Document the new attack
 vector controls

[AMD Official Use Only - AMD Internal Distribution Only]

> -----Original Message-----
> From: Josh Poimboeuf <jpoimboe@...nel.org>
> Sent: Monday, April 14, 2025 6:51 PM
> To: Kaplan, David <David.Kaplan@....com>
> Cc: Thomas Gleixner <tglx@...utronix.de>; Borislav Petkov <bp@...en8.de>;
> Peter Zijlstra <peterz@...radead.org>; Pawan Gupta
> <pawan.kumar.gupta@...ux.intel.com>; Ingo Molnar <mingo@...hat.com>; Dave
> Hansen <dave.hansen@...ux.intel.com>; x86@...nel.org; H . Peter Anvin
> <hpa@...or.com>; linux-kernel@...r.kernel.org; Brendan Jackman
> <jackmanb@...gle.com>; Derek Manwaring <derekmn@...zon.com>
> Subject: Re: [PATCH v4 17/36] Documentation/x86: Document the new attack
> vector controls
>
> Caution: This message originated from an External Source. Use proper caution
> when opening attachments, clicking links, or responding.
>
>
> On Mon, Apr 14, 2025 at 09:15:54PM +0000, Kaplan, David wrote:
> > [AMD Official Use Only - AMD Internal Distribution Only]
> >
> > > -----Original Message-----
> > > From: Josh Poimboeuf <jpoimboe@...nel.org>
> > > Sent: Thursday, April 10, 2025 1:15 PM
> > > To: Kaplan, David <David.Kaplan@....com>
> > > Cc: Thomas Gleixner <tglx@...utronix.de>; Borislav Petkov
> > > <bp@...en8.de>; Peter Zijlstra <peterz@...radead.org>; Pawan Gupta
> > > <pawan.kumar.gupta@...ux.intel.com>; Ingo Molnar <mingo@...hat.com>;
> > > Dave Hansen <dave.hansen@...ux.intel.com>; x86@...nel.org; H . Peter
> > > Anvin <hpa@...or.com>; linux-kernel@...r.kernel.org; Brendan Jackman
> > > <jackmanb@...gle.com>; Derek Manwaring <derekmn@...zon.com>
> > > Subject: Re: [PATCH v4 17/36] Documentation/x86: Document the new
> > > attack vector controls
> > >
> > > Caution: This message originated from an External Source. Use proper
> > > caution when opening attachments, clicking links, or responding.
> > >
> > >
> > > On Mon, Mar 10, 2025 at 11:40:04AM -0500, David Kaplan wrote:
> > > > +=============== ============== ============ =============
> > > ============== ============
> > > > +Vulnerability   User-to-Kernel User-to-User Guest-to-Host Guest-to-Guest
> > > Cross-Thread
> > > > +=============== ============== ============ =============
> > > ============== ============
> > > > +BHI                   X                           X
> > > > +GDS                   X              X            X              X        (Note 1)
> > > > +L1TF                  X                           X                       (Note 2)
> > > > +MDS                   X              X            X              X        (Note 2)
> > > > +MMIO                  X              X            X              X        (Note 2)
> > > > +Meltdown              X
> > > > +Retbleed              X                           X                       (Note 3)
> > > > +RFDS                  X              X            X              X
> > > > +Spectre_v1            X
> > > > +Spectre_v2            X                           X
> > > > +Spectre_v2_user                      X                           X        (Note 1)
> > > > +SRBDS                 X              X            X              X
> > > > +SRSO                  X                           X
> > > > +SSB (Note 4)
> > >
> > > Any reason not to put the "Note 4" in the same column as the others?
> > >
> >
> > The other notes are about cross-thread mitigation specifically and those notes
> refer to the SMT aspects of those issues.
> >
> > Note 4 in this case is about the SSB vulnerability itself, explaining
> > that by default there is no mitigation for any case.  I was concerned
> > that including SSB but without any X's in any of the columns would be
> > confusing, so the note attempted to explain that there were no default
> > mitigations for SSB under any attack vector.
>
> Putting the note there makes it a lot harder to see it.  And I think the lack of X's is
> accurate, no?
>

It is, it's just rather unique compared to the other bugs.  I could remove the note entirely, but I was concerned that might look odd because it'd be the only bug that isn't mitigated under any of the attack vectors.  And that's really just because the current default is not to mitigate that one.

--David Kaplan