linux-kernel - Re: [PATCH 22/23] x86/nospec: Refactor UNTRAIN_RET[

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Date:   Fri, 25 Aug 2023 21:22:10 +0300
From:   Nikolay Borisov <nik.borisov@...e.com>
To:     Josh Poimboeuf <jpoimboe@...nel.org>, x86@...nel.org
Cc:     linux-kernel@...r.kernel.org, Borislav Petkov <bp@...en8.de>,
        Peter Zijlstra <peterz@...radead.org>,
        Babu Moger <babu.moger@....com>,
        Paolo Bonzini <pbonzini@...hat.com>,
        Sean Christopherson <seanjc@...gle.com>, David.Kaplan@....com,
        Andrew Cooper <andrew.cooper3@...rix.com>,
        gregkh@...uxfoundation.org, Thomas Gleixner <tglx@...utronix.de>
Subject: Re: [PATCH 22/23] x86/nospec: Refactor UNTRAIN_RET[_*]



On 25.08.23 г. 10:01 ч., Josh Poimboeuf wrote:
> Factor out the UNTRAIN_RET[_*] common bits into a helper macro.
> 
> Signed-off-by: Josh Poimboeuf <jpoimboe@...nel.org>
> ---
>   arch/x86/include/asm/nospec-branch.h | 31 +++++++++-------------------
>   1 file changed, 10 insertions(+), 21 deletions(-)
> 
> diff --git a/arch/x86/include/asm/nospec-branch.h b/arch/x86/include/asm/nospec-branch.h
> index 51e3f1a287d2..dcc78477a38d 100644
> --- a/arch/x86/include/asm/nospec-branch.h
> +++ b/arch/x86/include/asm/nospec-branch.h
> @@ -288,35 +288,24 @@
>    * As such, this must be placed after every *SWITCH_TO_KERNEL_CR3 at a point
>    * where we have a stack but before any RET instruction.
>    */
> -.macro UNTRAIN_RET
> +.macro __UNTRAIN_RET ibpb_feature, call_depth_insns
>   #if defined(CONFIG_RETHUNK) || defined(CONFIG_CPU_IBPB_ENTRY)
>   	VALIDATE_UNRET_END
>   	ALTERNATIVE_3 "",						\
>   		      CALL_UNTRAIN_RET, X86_FEATURE_UNRET,		\
> -		      "call entry_ibpb", X86_FEATURE_ENTRY_IBPB,	\
> -		     __stringify(RESET_CALL_DEPTH), X86_FEATURE_CALL_DEPTH
> +		      "call entry_ibpb", \ibpb_feature,			\
> +		     __stringify(\call_depth_insns), X86_FEATURE_CALL_DEPTH

so this becomes __stringify(__stringify(RESET_CALL_DEPTH)) etc.

Meaning in the high-level macros you want to pass just 
RESET_CALL_DEPTH/RESET_CALL_DEPTH_FROM_CALL ?

>   #endif
>   .endm
>   
> -.macro UNTRAIN_RET_VM
> -#if defined(CONFIG_RETHUNK) || defined(CONFIG_CPU_IBPB_ENTRY)
> -	VALIDATE_UNRET_END
> -	ALTERNATIVE_3 "",						\
> -		      CALL_UNTRAIN_RET, X86_FEATURE_UNRET,		\
> -		      "call entry_ibpb", X86_FEATURE_IBPB_ON_VMEXIT,	\
> -		      __stringify(RESET_CALL_DEPTH), X86_FEATURE_CALL_DEPTH
> -#endif
> -.endm
> +#define UNTRAIN_RET \
> +	__UNTRAIN_RET X86_FEATURE_ENTRY_IBPB, __stringify(RESET_CALL_DEPTH)
>   
> -.macro UNTRAIN_RET_FROM_CALL
> -#if defined(CONFIG_RETHUNK) || defined(CONFIG_CPU_IBPB_ENTRY)
> -	VALIDATE_UNRET_END
> -	ALTERNATIVE_3 "",						\
> -		      CALL_UNTRAIN_RET, X86_FEATURE_UNRET,		\
> -		      "call entry_ibpb", X86_FEATURE_ENTRY_IBPB,	\
> -		      __stringify(RESET_CALL_DEPTH_FROM_CALL), X86_FEATURE_CALL_DEPTH
> -#endif
> -.endm
> +#define UNTRAIN_RET_VM \
> +	__UNTRAIN_RET X86_FEATURE_IBPB_ON_VMEXIT, __stringify(RESET_CALL_DEPTH)
> +
> +#define UNTRAIN_RET_FROM_CALL \
> +	__UNTRAIN_RET X86_FEATURE_ENTRY_IBPB, __stringify(RESET_CALL_DEPTH_FROM_CALL)
>   
>   
>   .macro CALL_DEPTH_ACCOUNT