linux-kernel - Re: [tip:x86/pti] x86/retpoline: Fill return stack buffer on vmexit

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Date:   Sun, 14 Jan 2018 15:50:09 +0100
From:   Borislav Petkov <bp@...en8.de>
To:     dwmw@...zon.co.uk
Cc:     tim.c.chen@...ux.intel.com, pjt@...gle.com, jikos@...nel.org,
        gregkh@...ux-foundation.org, dave.hansen@...el.com,
        mingo@...nel.org, riel@...hat.com, luto@...capital.net,
        torvalds@...ux-foundation.org, ak@...ux.intel.com,
        keescook@...gle.com, jpoimboe@...hat.com, peterz@...radead.org,
        tglx@...utronix.de, hpa@...or.com, linux-kernel@...r.kernel.org,
        linux-tip-commits@...r.kernel.org
Subject: Re: [tip:x86/pti] x86/retpoline: Fill return stack buffer on vmexit

On Fri, Jan 12, 2018 at 03:37:49AM -0800, tip-bot for David Woodhouse wrote:
> Commit-ID:  117cc7a908c83697b0b737d15ae1eb5943afe35b
> Gitweb:     https://git.kernel.org/tip/117cc7a908c83697b0b737d15ae1eb5943afe35b
> Author:     David Woodhouse <dwmw@...zon.co.uk>
> AuthorDate: Fri, 12 Jan 2018 11:11:27 +0000
> Committer:  Thomas Gleixner <tglx@...utronix.de>
> CommitDate: Fri, 12 Jan 2018 12:33:37 +0100
> 
> x86/retpoline: Fill return stack buffer on vmexit

...

> + /*
> +  * A simpler FILL_RETURN_BUFFER macro. Don't make people use the CPP
> +  * monstrosity above, manually.
> +  */
> +.macro FILL_RETURN_BUFFER reg:req nr:req ftr:req
> +#ifdef CONFIG_RETPOLINE
> +	ANNOTATE_NOSPEC_ALTERNATIVE
> +	ALTERNATIVE "jmp .Lskip_rsb_\@",				\
> +		__stringify(__FILL_RETURN_BUFFER(\reg,\nr,%_ASM_SP))	\
> +		\ftr
> +.Lskip_rsb_\@:
> +#endif
> +.endm

Looks unused to me. Was it ever gound to be used? If not:

---
--- a/arch/x86/include/asm/nospec-branch.h
+++ b/arch/x86/include/asm/nospec-branch.h
@@ -121,20 +121,6 @@
 #endif
 .endm
 
- /*
-  * A simpler FILL_RETURN_BUFFER macro. Don't make people use the CPP
-  * monstrosity above, manually.
-  */
-.macro FILL_RETURN_BUFFER reg:req nr:req ftr:req
-#ifdef CONFIG_RETPOLINE
-	ANNOTATE_NOSPEC_ALTERNATIVE
-	ALTERNATIVE "jmp .Lskip_rsb_\@",				\
-		__stringify(__FILL_RETURN_BUFFER(\reg,\nr,%_ASM_SP))	\
-		\ftr
-.Lskip_rsb_\@:
-#endif
-.endm
-
 #else /* __ASSEMBLY__ */
 
 #define ANNOTATE_NOSPEC_ALTERNATIVE				\

-- 
Regards/Gruss,
    Boris.

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