linux-kernel - Re: [PATCH v3 12/35] x86/bugs: Restructure retbleed mitigation

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Message-ID: <20250110184545.2c7a9976@pumpkin>
Date: Fri, 10 Jan 2025 18:45:45 +0000
From: David Laight <david.laight.linux@...il.com>
To: Pawan Gupta <pawan.kumar.gupta@...ux.intel.com>
Cc: David Kaplan <david.kaplan@....com>, 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>,
 linux-kernel@...r.kernel.org
Subject: Re: [PATCH v3 12/35] x86/bugs: Restructure retbleed mitigation

On Wed, 8 Jan 2025 21:22:37 -0800
Pawan Gupta <pawan.kumar.gupta@...ux.intel.com> wrote:

> On Wed, Jan 08, 2025 at 02:24:52PM -0600, David Kaplan wrote:
> [...]
> > @@ -1064,6 +1063,7 @@ enum spectre_v2_mitigation spectre_v2_enabled __ro_after_init = SPECTRE_V2_NONE;
> >  
> >  enum retbleed_mitigation {
> >  	RETBLEED_MITIGATION_NONE,
> > +	RETBLEED_MITIGATION_AUTO,  
> 
> This new enum ...
> 
> >  	RETBLEED_MITIGATION_UNRET,
> >  	RETBLEED_MITIGATION_IBPB,
> >  	RETBLEED_MITIGATION_IBRS,
> > @@ -1071,14 +1071,6 @@ enum retbleed_mitigation {
> >  	RETBLEED_MITIGATION_STUFF,
> >  };
...
> >  static const char * const retbleed_strings[] = {
> >  	[RETBLEED_MITIGATION_NONE]	= "Vulnerable",
> >  	[RETBLEED_MITIGATION_UNRET]	= "Mitigation: untrained return thunk",  
> 
> ... does not have a corresponding entry in the strings array. AUTO is the
> default, and it is possible that mitigation mode can stay AUTO throughout
> the retbleed mitigation selection depending on cmdline and CONFIGs. e.g.
> retbleed=stuff and spectre_v2=off.

It is possible to use 'a bit of cpp magic' to put the definitions on one line.
Something like:
#define RETBLEED_MITIGATION(x) \
	x(NONE, "Vulnerable") \
	x(AUTO, "xxxx") \
	x(UNRET, "Mitigation: untrained return thunk") \
	...

#define X(NAME, msg) RETBLEED_MITIGATION_##NAME),
enum retbleed_mitigation { RETBLEED_MITIGATION(X) };
#undef X

#define X(NAME, msg) [RETBLEED_MITIGATION_##NAME] = msg,
static const char * const retbleed_strings[] = { RETBLEED_MITIGATION(X) };
#undef X

Then you can't lose message texts even when they are in a different file.
The lower case name (for the strcmp() loop) can also be added.

(and don't let the rust bindgen near it :-)

	David