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

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Message-ID: <20250110203058.66cd7zlajfbpqf5k@desk>
Date: Fri, 10 Jan 2025 12:30:58 -0800
From: Pawan Gupta <pawan.kumar.gupta@...ux.intel.com>
To: David Laight <david.laight.linux@...il.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 Fri, Jan 10, 2025 at 06:45:45PM +0000, David Laight wrote:
> 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 :-)

Wow, this is mind blowing!