linux-kernel - Re: [PATCH v3] x86/bugs: Default retbleed to =stuff when retpoline is enabled

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Date: Wed, 3 Apr 2024 07:50:49 -0700
From: Pawan Gupta <pawan.kumar.gupta@...ux.intel.com>
To: Nikolay Borisov <nik.borisov@...e.com>
Cc: Thomas Gleixner <tglx@...utronix.de>, Borislav Petkov <bp@...en8.de>,
	Peter Zijlstra <peterz@...radead.org>,
	Josh Poimboeuf <jpoimboe@...nel.org>,
	Ingo Molnar <mingo@...hat.com>,
	Dave Hansen <dave.hansen@...ux.intel.com>, x86@...nel.org,
	"H. Peter Anvin" <hpa@...or.com>,
	Daniel Sneddon <daniel.sneddon@...ux.intel.com>,
	antonio.gomez.iglesias@...ux.intel.com,
	alyssa.milburn@...ux.intel.com, andrew.cooper3@...rix.com,
	linux-kernel@...r.kernel.org,
	Alyssa Milburn <alyssa.milburn@...el.com>, stable@...nel.org
Subject: Re: [PATCH v3] x86/bugs: Default retbleed to =stuff when retpoline
 is enabled

On Wed, Apr 03, 2024 at 05:32:40PM +0300, Nikolay Borisov wrote:
> 
> 
> On 3.04.24 г. 8:54 ч., Pawan Gupta wrote:
> > On Intel systems when retpoline mitigation is enabled for spectre-v2,
> > retbleed=auto does not enable RSB stuffing. This may make the system
> > vulnerable to retbleed. Retpoline is not the default mitigation when
> > IBRS is present, but in virtualized cases a VMM can hide IBRS from
> > guests, resulting in guest deploying retpoline by default. Even if IBRS
> > is enumerated, a user can still select spectre_v2=retpoline.
> > 
> > As with other mitigations, mitigate retbleed by default. On Intel
> > systems when retpoline is enabled, and retbleed mitigation is set to
> > auto, enable Call Depth Tracking and RSB stuffing i.e. retbleed=stuff
> > mitigation. For AMD/Hygon auto mode already selects the appropriate
> > mitigation.
> > 
> > Reported-by: Alyssa Milburn <alyssa.milburn@...el.com>
> > Cc: stable@...nel.org
> > Signed-off-by: Pawan Gupta <pawan.kumar.gupta@...ux.intel.com>
> 
> Reviewed-by: Nikolay Borisov <nik.borisov@...e.com>

Thanks.