linux-kernel - RE: [RFC PATCH 01/56] Documentation/admin-guide: Add documentation

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Message-ID:
 <LV3PR12MB9265578BE201F1D5E1D7488194F5A@LV3PR12MB9265.namprd12.prod.outlook.com>
Date: Mon, 20 Oct 2025 13:53:11 +0000
From: "Kaplan, David" <David.Kaplan@....com>
To: Borislav Petkov <bp@...en8.de>
CC: Thomas Gleixner <tglx@...utronix.de>, Peter Zijlstra
	<peterz@...radead.org>, Josh Poimboeuf <jpoimboe@...nel.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>, Alexander Graf <graf@...zon.com>, Boris
 Ostrovsky <boris.ostrovsky@...cle.com>, "linux-kernel@...r.kernel.org"
	<linux-kernel@...r.kernel.org>
Subject: RE: [RFC PATCH 01/56] Documentation/admin-guide: Add documentation

[AMD Official Use Only - AMD Internal Distribution Only]

> -----Original Message-----
> From: Borislav Petkov <bp@...en8.de>
> Sent: Saturday, October 18, 2025 8:39 AM
> To: Kaplan, David <David.Kaplan@....com>
> Cc: Thomas Gleixner <tglx@...utronix.de>; Peter Zijlstra <peterz@...radead.org>;
> Josh Poimboeuf <jpoimboe@...nel.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>; Alexander Graf <graf@...zon.com>; Boris Ostrovsky
> <boris.ostrovsky@...cle.com>; linux-kernel@...r.kernel.org
> Subject: Re: [RFC PATCH 01/56] Documentation/admin-guide: Add documentation
>
> Caution: This message originated from an External Source. Use proper caution
> when opening attachments, clicking links, or responding.
>
>
> On Mon, Oct 13, 2025 at 09:33:49AM -0500, David Kaplan wrote:
> > +Move Policy To Userspace
> > +^^^^^^^^^^^^^^^^^^^^^^^^
> > +
> > +Mitigation choices are related to the security policy and posture of the system.
> > +Most mitigations are only necessary on shared, multi-user systems if untrusted
> > +code may be run on the system, such as through untrusted userspace or
> untrusted
> > +virtual machines.  The kernel may not know how the system will be used on
> boot,
>                                                                         ^^^^^^^^^^
>
> "after it has been booted" I'd say.

Ack

>
> > +and therefore must adopt a strong security posture for safety.
> > +
> > +With dynamic mitigations, userspace can re-select mitigations once the needs of
> > +the system can be determined and more policy information is available.
> > +
> > +Mitigation Testing
> > +^^^^^^^^^^^^^^^^^^
> > +
> > +Dynamic mitigation support makes it easy to toggle individual mitigations or
> > +choose between different mitigation options without the expense of a reboot or
> > +kexec.  This may be useful when evaluating the performance of various
> > +mitigation options.  It can also be useful for performing bug fixes without a
>
> "for fixing bugs in the mitigations themselves" - simpler
>
> > +reboot, in case a particular mitigation is undesired or buggy.
>

Ack.  Although to be clear, all it can do is select a different mitigation.  For instance, if there was a bug in safe-RET, it can't fix that bug.  But it could allow selecting a different SRSO mitigation.

Thanks
--David Kaplan