linux-kernel - Re: [PATCH v11 06/11] x86/CPU: Adapt assembly for PIE support

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Date:   Mon, 2 Mar 2020 20:58:00 -0800
From:   Kees Cook <keescook@...omium.org>
To:     Thomas Garnier <thgarnie@...omium.org>
Cc:     kernel-hardening@...ts.openwall.com, kristen@...ux.intel.com,
        Thomas Gleixner <tglx@...utronix.de>,
        Ingo Molnar <mingo@...hat.com>, Borislav Petkov <bp@...en8.de>,
        "H. Peter Anvin" <hpa@...or.com>, x86@...nel.org,
        Andy Lutomirski <luto@...nel.org>,
        "Peter Zijlstra (Intel)" <peterz@...radead.org>,
        Len Brown <len.brown@...el.com>, linux-kernel@...r.kernel.org
Subject: Re: [PATCH v11 06/11] x86/CPU: Adapt assembly for PIE support

On Thu, Feb 27, 2020 at 04:00:51PM -0800, Thomas Garnier wrote:
> Change the assembly code to use only relative references of symbols for the
> kernel to be PIE compatible.
> 
> Signed-off-by: Thomas Garnier <thgarnie@...omium.org>

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

-Kees

> ---
>  arch/x86/include/asm/processor.h | 6 ++++--
>  1 file changed, 4 insertions(+), 2 deletions(-)
> 
> diff --git a/arch/x86/include/asm/processor.h b/arch/x86/include/asm/processor.h
> index 09705ccc393c..fdf6366c482d 100644
> --- a/arch/x86/include/asm/processor.h
> +++ b/arch/x86/include/asm/processor.h
> @@ -746,11 +746,13 @@ static inline void sync_core(void)
>  		"pushfq\n\t"
>  		"mov %%cs, %0\n\t"
>  		"pushq %q0\n\t"
> -		"pushq $1f\n\t"
> +		"leaq 1f(%%rip), %q0\n\t"
> +		"pushq %q0\n\t"
>  		"iretq\n\t"
>  		UNWIND_HINT_RESTORE
>  		"1:"
> -		: "=&r" (tmp), ASM_CALL_CONSTRAINT : : "cc", "memory");
> +		: "=&r" (tmp), ASM_CALL_CONSTRAINT
> +		: : "cc", "memory");
>  #endif
>  }
>  
> -- 
> 2.25.1.481.gfbce0eb801-goog
> 

-- 
Kees Cook