linux-kernel - Re: [PATCH v7 04/12] x86: relocate_kernel

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Message-ID: <201906101433.0A1A27960@keescook>
Date:   Mon, 10 Jun 2019 14:33:05 -0700
From:   Kees Cook <keescook@...omium.org>
To:     Thomas Garnier <thgarnie@...omium.org>
Cc:     kernel-hardening@...ts.openwall.com, kristen@...ux.intel.com,
        Thomas Garnier <thgarnie@...gle.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,
        linux-kernel@...r.kernel.org
Subject: Re: [PATCH v7 04/12] x86: relocate_kernel - Adapt assembly for PIE
 support

On Mon, May 20, 2019 at 04:19:29PM -0700, Thomas Garnier wrote:
> From: Thomas Garnier <thgarnie@...gle.com>
> 
> Change the assembly code to use only absolute references of symbols for the
> kernel to be PIE compatible.
> 
> Position Independent Executable (PIE) support will allow to extend the
> KASLR randomization range below 0xffffffff80000000.
> 
> Signed-off-by: Thomas Garnier <thgarnie@...gle.com>

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

-Kees

> ---
>  arch/x86/kernel/relocate_kernel_64.S | 2 +-
>  1 file changed, 1 insertion(+), 1 deletion(-)
> 
> diff --git a/arch/x86/kernel/relocate_kernel_64.S b/arch/x86/kernel/relocate_kernel_64.S
> index 11eda21eb697..3320368b6ec9 100644
> --- a/arch/x86/kernel/relocate_kernel_64.S
> +++ b/arch/x86/kernel/relocate_kernel_64.S
> @@ -208,7 +208,7 @@ identity_mapped:
>  	movq	%rax, %cr3
>  	lea	PAGE_SIZE(%r8), %rsp
>  	call	swap_pages
> -	movq	$virtual_mapped, %rax
> +	movabsq	$virtual_mapped, %rax
>  	pushq	%rax
>  	ret
>  
> -- 
> 2.21.0.1020.gf2820cf01a-goog
> 

-- 
Kees Cook