linux-kernel - Re: [PATCH v3 5/6] x86/bugs: Don't fill RSB on context switch with eIBRS

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Message-ID: <80e2557d-b4b0-4097-9662-8772d2af25fe@suse.com>
Date: Tue, 8 Apr 2025 16:51:43 +0300
From: Nikolay Borisov <nik.borisov@...e.com>
To: Josh Poimboeuf <jpoimboe@...nel.org>, x86@...nel.org
Cc: 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, pawan.kumar.gupta@...ux.intel.com,
 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 v3 5/6] x86/bugs: Don't fill RSB on context switch with
 eIBRS



On 2.04.25 г. 21:19 ч., 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 either the prev or the next task has opted in to protection.  RSB
> filling 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, so remove it.
> 
> Suggested-by: Pawan Gupta <pawan.kumar.gupta@...ux.intel.com>
> Reviewed-by: Pawan Gupta <pawan.kumar.gupta@...ux.intel.com>
> Reviewed-by: Amit Shah <amit.shah@....com>
> Signed-off-by: Josh Poimboeuf <jpoimboe@...nel.org>

Reviewed-by: Nikolay Borisov <nik.borisov@...e.com>