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

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Message-ID: <20240210004022.aff2dnr6dzwq5gkq@treble>
Date: Fri, 9 Feb 2024 16:40:22 -0800
From: Josh Poimboeuf <jpoimboe@...nel.org>
To: Pawan Gupta <pawan.kumar.gupta@...ux.intel.com>
Cc: Thomas Gleixner <tglx@...utronix.de>, Borislav Petkov <bp@...en8.de>,
	Peter Zijlstra <peterz@...radead.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>
Subject: Re: [PATCH] x86/bugs: Default retbleed to =stuff when retpoline is
 auto enabled

On Fri, Feb 09, 2024 at 12:33:46PM -0800, Pawan Gupta wrote:
> On Fri, Feb 09, 2024 at 10:56:25AM -0800, Josh Poimboeuf wrote:
> > On Thu, Feb 08, 2024 at 05:12:15PM -0800, Pawan Gupta wrote:
> > > +			   spectre_v2_enabled == SPECTRE_V2_RETPOLINE) {
> > > +			if (IS_ENABLED(CONFIG_CALL_DEPTH_TRACKING))
> > > +				retbleed_mitigation = RETBLEED_MITIGATION_STUFF;
> > > +			else
> > > +				pr_err("WARNING: Retpoline enabled, but kernel not compiled with CALL_DEPTH_TRACKING.\n");
> > 
> > If retbleed is vulnerable then the sysfs file should show that.
> 
> It does shows vulnerable, retbleed_mitigation is not set to
> RETBLEED_MITIGATION_STUFF for CONFIG_CALL_DEPTH_TRACKING=n.

Ah right, in that case retbleed_mitigation still has its initialized
value of RETBLEED_MITIGATION_NONE.

> > Also, I think this pr_err() is redundant with RETBLEED_INTEL_MSG and can
> > be removed.
> 
> IMO, they both serve a different purpose, RETBLEED_INTEL_MSG is a
> generic warning, and the message with !CONFIG_CALL_DEPTH_TRACKING hints
> a corrective action.
> 
> If you look at "case RETBLEED_CMD_STUFF" it also prints a separate warning for
> !CONFIG_CALL_DEPTH_TRACKING:

Yep, makes sense.

-- 
Josh