linux-kernel - Re: [PATCH 1/3] x86/execmem: don't use PAGE

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Message-ID: <aDdHdwf8REvdu5FF@kernel.org>
Date: Wed, 28 May 2025 20:27:19 +0300
From: Mike Rapoport <rppt@...nel.org>
To: Juergen Gross <jgross@...e.com>
Cc: linux-kernel@...r.kernel.org, x86@...nel.org, xin@...or.com,
	Dave Hansen <dave.hansen@...ux.intel.com>,
	Andy Lutomirski <luto@...nel.org>,
	Peter Zijlstra <peterz@...radead.org>,
	Thomas Gleixner <tglx@...utronix.de>,
	Ingo Molnar <mingo@...hat.com>, Borislav Petkov <bp@...en8.de>,
	"H. Peter Anvin" <hpa@...or.com>, stable@...r.kernel.org
Subject: Re: [PATCH 1/3] x86/execmem: don't use PAGE_KERNEL protection for
 code pages

On Wed, May 28, 2025 at 02:35:55PM +0200, Juergen Gross wrote:
> In case X86_FEATURE_PSE isn't available (e.g. when running as a Xen
> PV guest), execmem_arch_setup() will fall back to use PAGE_KERNEL
> protection for the EXECMEM_MODULE_TEXT range.
> 
> This will result in attempts to execute code with the NX bit set in
> case of ITS mitigation being applied.
> 
> Avoid this problem by using PAGE_KERNEL_EXEC protection instead,
> which will not set the NX bit.
> 
> Cc: <stable@...r.kernel.org>
> Reported-by: Xin Li <xin@...or.com>
> Fixes: 5185e7f9f3bd ("x86/module: enable ROX caches for module text on 64 bit")
> Signed-off-by: Juergen Gross <jgross@...e.com>
> ---
>  arch/x86/mm/init.c | 2 +-
>  1 file changed, 1 insertion(+), 1 deletion(-)
> 
> diff --git a/arch/x86/mm/init.c b/arch/x86/mm/init.c
> index 7456df985d96..f5012ae31d8b 100644
> --- a/arch/x86/mm/init.c
> +++ b/arch/x86/mm/init.c
> @@ -1089,7 +1089,7 @@ struct execmem_info __init *execmem_arch_setup(void)
>  		pgprot = PAGE_KERNEL_ROX;
>  		flags = EXECMEM_KASAN_SHADOW | EXECMEM_ROX_CACHE;
>  	} else {
> -		pgprot = PAGE_KERNEL;
> +		pgprot = PAGE_KERNEL_EXEC;

Please don't. Everything except ITS can work with PAGE_KENREL so the fix
should be on ITS side. 

>  		flags = EXECMEM_KASAN_SHADOW;
>  	}
>  
> -- 
> 2.43.0
> 

-- 
Sincerely yours,
Mike.