linux-kernel - Re: [RFC][PATCH 01/17] x86/alternative: Unconditional custom return thunk

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Date:   Wed, 9 Aug 2023 12:31:21 +0300
From:   Nikolay Borisov <nik.borisov@...e.com>
To:     Peter Zijlstra <peterz@...radead.org>, x86@...nel.org
Cc:     linux-kernel@...r.kernel.org, David.Kaplan@....com,
        Andrew.Cooper3@...rix.com, jpoimboe@...nel.org,
        gregkh@...uxfoundation.org
Subject: Re: [RFC][PATCH 01/17] x86/alternative: Unconditional custom return
 thunk



On 9.08.23 г. 10:12 ч., Peter Zijlstra wrote:
> There is infrastructure to rewrite return thunks to point to any
> random thunk one desires, unwrap that from CALL_THUNKS, which up to
> now was the sole user of that.
> 
> Signed-off-by: Peter Zijlstra (Intel) <peterz@...radead.org>
> ---
>   arch/x86/include/asm/nospec-branch.h |    4 ----
>   arch/x86/kernel/alternative.c        |    2 --
>   2 files changed, 6 deletions(-)
> 
> --- a/arch/x86/include/asm/nospec-branch.h
> +++ b/arch/x86/include/asm/nospec-branch.h
> @@ -347,11 +347,7 @@ extern void srso_untrain_ret(void);
>   extern void srso_untrain_ret_alias(void);
>   extern void entry_ibpb(void);
>   
> -#ifdef CONFIG_CALL_THUNKS
>   extern void (*x86_return_thunk)(void);
> -#else
> -#define x86_return_thunk	(&__x86_return_thunk)
> -#endif
>   
>   #ifdef CONFIG_CALL_DEPTH_TRACKING
>   extern void __x86_return_skl(void);
> --- a/arch/x86/kernel/alternative.c
> +++ b/arch/x86/kernel/alternative.c
> @@ -698,9 +698,7 @@ void __init_or_module noinline apply_ret
>   
>   #ifdef CONFIG_RETHUNK
>   
> -#ifdef CONFIG_CALL_THUNKS
>   void (*x86_return_thunk)(void) __ro_after_init = &__x86_return_thunk;
> -#endif
>   
>   /*
>    * Rewrite the compiler generated return thunk tail-calls.
> 
> 


Reviewed-by: Nikolay Borisov <nik.borisov@...e.com>