linux-kernel - Re: [PATCH v2 1/2] x86/bugs: Don't fill RSB on VMEXIT with eIBRS+retpoline

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Message-ID: <20241203112015.GBZ07pb74AGR-TDWt7@fat_crate.local>
Date: Tue, 3 Dec 2024 12:20:15 +0100
From: Borislav Petkov <bp@...en8.de>
To: Pawan Gupta <pawan.kumar.gupta@...ux.intel.com>
Cc: Josh Poimboeuf <jpoimboe@...nel.org>, x86@...nel.org,
	linux-kernel@...r.kernel.org, amit@...nel.org, kvm@...r.kernel.org,
	amit.shah@....com, thomas.lendacky@....com, 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 v2 1/2] x86/bugs: Don't fill RSB on VMEXIT with
 eIBRS+retpoline

On Mon, Dec 02, 2024 at 03:35:21PM -0800, Pawan Gupta wrote:
> It is in this doc:
> 
>   https://www.intel.com/content/www/us/en/developer/articles/technical/software-security-guidance/technical-documentation/indirect-branch-restricted-speculation.html
> 

I hope those URLs remain more stable than past experience shows.

>   "Processors with enhanced IBRS still support the usage model where IBRS is
>   set only in the OS/VMM for OSes that enable SMEP. To do this, such
>   processors will ensure that guest behavior cannot control the RSB after a
>   VM exit once IBRS is set, even if IBRS was not set at the time of the VM
>   exit."

ACK, thanks.

Now, can we pls add those excerpts to Documentation/ and point to them from
the code so that it is crystal clear why it is ok?

Thx.

-- 
Regards/Gruss,
    Boris.

https://people.kernel.org/tglx/notes-about-netiquette