linux-kernel - Re: [PATCH 2/2] x86/bugs: Don't WARN() when overwriting retbleed_return_thunk with srso_return

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Message-ID: <20250516154034.GEaCdccm27F_hgZ8c9@fat_crate.local>
Date: Fri, 16 May 2025 17:40:34 +0200
From: Borislav Petkov <bp@...en8.de>
To: "Kaplan, David" <David.Kaplan@....com>
Cc: Suraj Jitindar Singh <surajjs@...zon.com>,
	"linux-kernel@...r.kernel.org" <linux-kernel@...r.kernel.org>,
	"x86@...nel.org" <x86@...nel.org>,
	Thomas Gleixner <tglx@...utronix.de>,
	Peter Zijlstra <peterz@...radead.org>,
	Josh Poimboeuf <jpoimboe@...nel.org>,
	Pawan Gupta <pawan.kumar.gupta@...ux.intel.com>,
	Ingo Molnar <mingo@...hat.com>,
	Dave Hansen <dave.hansen@...ux.intel.com>,
	"stable@...r.kernel.org" <stable@...r.kernel.org>
Subject: Re: [PATCH 2/2] x86/bugs: Don't WARN() when overwriting
 retbleed_return_thunk with srso_return_thunk

On Fri, May 16, 2025 at 03:18:30PM +0000, Kaplan, David wrote:
> Hmm.  Since SRSO is kind of a superset of retbleed, it might make sense to
> create a new mitigation, RETBLEED_MITIGATION_SAFE_RET.
> 
> retbleed_update_mitigation() can change its mitigation to this if
> srso_mitigation is SAFE_RET (or SAFE_RET_UCODE_NEEDED).
> RETBLEED_MITIGATION_SAFE_RET can do nothing in retbleed_apply_mitigation()
> because it means that srso is taking care of things.  Thoughts?
> 
> This also made me realize there's another minor missing interaction here,
> which is that if spec_rstack_overflow=ibpb, then that should set
> retbleed_mitigation to IBPB as well.

Ok, this sounds like we should expedite our srso mitigation cleanup
intentions. :-)

Lemme find you on chat...

-- 
Regards/Gruss,
    Boris.

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