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Date:   Mon, 2 Mar 2020 20:59:59 -0800
From:   Kees Cook <keescook@chromium.org>
To:     Thomas Garnier <thgarnie@chromium.org>
Cc:     kernel-hardening@lists.openwall.com, kristen@linux.intel.com,
        Thomas Gleixner <tglx@linutronix.de>,
        Ingo Molnar <mingo@redhat.com>, Borislav Petkov <bp@alien8.de>,
        "H. Peter Anvin" <hpa@zytor.com>, x86@kernel.org,
        Miguel Ojeda <miguel.ojeda.sandonis@gmail.com>,
        Rasmus Villemoes <linux@rasmusvillemoes.dk>,
        Peter Zijlstra <peterz@infradead.org>,
        linux-kernel@vger.kernel.org
Subject: Re: [PATCH v11 11/11] x86/alternatives: Adapt assembly for PIE
 support
Message-ID: <202003022059.67FCB9CB75@keescook>
References: <20200228000105.165012-1-thgarnie@chromium.org>
 <20200228000105.165012-12-thgarnie@chromium.org>
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On Thu, Feb 27, 2020 at 04:00:56PM -0800, Thomas Garnier wrote:
> Change the assembly options to work with pointers instead of integers.
> The generated code is the same PIE just ensures input is a pointer.
> 
> Signed-off-by: Thomas Garnier <thgarnie@chromium.org>

Reviewed-by: Kees Cook <keescook@chromium.org>

-Kees

> ---
>  arch/x86/include/asm/alternative.h | 6 +++---
>  1 file changed, 3 insertions(+), 3 deletions(-)
> 
> diff --git a/arch/x86/include/asm/alternative.h b/arch/x86/include/asm/alternative.h
> index 13adca37c99a..43a148042656 100644
> --- a/arch/x86/include/asm/alternative.h
> +++ b/arch/x86/include/asm/alternative.h
> @@ -243,7 +243,7 @@ static inline int alternatives_text_reserved(void *start, void *end)
>  /* Like alternative_io, but for replacing a direct call with another one. */
>  #define alternative_call(oldfunc, newfunc, feature, output, input...)	\
>  	asm_inline volatile (ALTERNATIVE("call %P[old]", "call %P[new]", feature) \
> -		: output : [old] "i" (oldfunc), [new] "i" (newfunc), ## input)
> +		: output : [old] "X" (oldfunc), [new] "X" (newfunc), ## input)
>  
>  /*
>   * Like alternative_call, but there are two features and respective functions.
> @@ -256,8 +256,8 @@ static inline int alternatives_text_reserved(void *start, void *end)
>  	asm_inline volatile (ALTERNATIVE_2("call %P[old]", "call %P[new1]", feature1,\
>  		"call %P[new2]", feature2)				      \
>  		: output, ASM_CALL_CONSTRAINT				      \
> -		: [old] "i" (oldfunc), [new1] "i" (newfunc1),		      \
> -		  [new2] "i" (newfunc2), ## input)
> +		: [old] "X" (oldfunc), [new1] "X" (newfunc1),		      \
> +		  [new2] "X" (newfunc2), ## input)
>  
>  /*
>   * use this macro(s) if you need more than one output parameter
> -- 
> 2.25.1.481.gfbce0eb801-goog
> 

-- 
Kees Cook