linux-kernel - Re: [PATCH 1/2] x86/bugs: Don't fill RSB on VMEXIT with eIBRS+retpoline

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Message-ID: <20241120181238.n3xwpd6uticlaw4a@desk>
Date: Wed, 20 Nov 2024 10:12:38 -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 1/2] x86/bugs: Don't fill RSB on VMEXIT with
 eIBRS+retpoline

On Tue, Nov 19, 2024 at 11:27:50PM -0800, Josh Poimboeuf wrote:
> eIBRS protects against RSB underflow/poisoning attacks.  Adding
> retpoline to the mix doesn't change that.  Retpoline has a balanced
> CALL/RET anyway.
> 
> So the current full RSB filling on VMEXIT with eIBRS+retpoline is
> overkill.  Disable it (or do the VMEXIT_LITE mitigation if needed).
> 
> 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>