linux-kernel - Re: [PATCH 2/2] x86/bugs: Don't fill RSB on context switch with eIBRS

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Message-ID: <20241120184238.rddzpb7fhbhtqphr@desk>
Date: Wed, 20 Nov 2024 10:42:38 -0800
From: Pawan Gupta <pawan.kumar.gupta@...ux.intel.com>
To: Josh Poimboeuf <jpoimboe@...nel.org>
Cc: x86@...nel.org, linux-kernel@...r.kernel.org, amit@...nel.org,
	kvm@...r.kernel.org, amit.shah@....com, thomas.lendacky@....com,
	bp@...en8.de, tglx@...utronix.de, peterz@...radead.org,
	corbet@....net, mingo@...hat.com, dave.hansen@...ux.intel.com,
	hpa@...or.com, seanjc@...gle.com, pbonzini@...hat.com,
	daniel.sneddon@...ux.intel.com, kai.huang@...el.com,
	sandipan.das@....com, boris.ostrovsky@...cle.com,
	Babu.Moger@....com, david.kaplan@....com, dwmw@...zon.co.uk,
	andrew.cooper3@...rix.com
Subject: Re: [PATCH 2/2] x86/bugs: Don't fill RSB on context switch with eIBRS

On Tue, Nov 19, 2024 at 11:27:51PM -0800, Josh Poimboeuf wrote:
> User->user Spectre v2 attacks (including RSB) across context switches
> are already mitigated by IBPB in cond_mitigation(), if enabled globally
> or if at least one of the tasks has opted in to protection.  RSB filling

Is below less ambiguous?

s/if at least one of the tasks/if previous or the next task/

> without IBPB serves no purpose for protecting user space, as indirect
> branches are still vulnerable.
> 
> User->kernel RSB attacks are mitigated by eIBRS.  In which case the RSB
> filling on context switch isn't needed.  Fix that.
> 
> While at it, update and coalesce the comments describing the various RSB
> mitigations.
> 
> Suggested-by: Pawan Gupta <pawan.kumar.gupta@...ux.intel.com>
> Signed-off-by: Josh Poimboeuf <jpoimboe@...nel.org>

Reviewed-by: Pawan Gupta <pawan.kumar.gupta@...ux.intel.com>