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

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Message-ID: <137571b5-0665-4ddd-ae78-0b8530daa549@suse.com>
Date: Wed, 28 May 2025 20:22:08 +0200
From: Jürgen Groß <jgross@...e.com>
To: Mike Rapoport <rppt@...nel.org>
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 28.05.25 19:27, Mike Rapoport wrote:
> 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.

Hmm, maybe adding another element to execmem_info[] with the new
type EXECMEM_KERNEL_TEXT, specifying PAGE_KERNEL_EXEC if !PSE?

Juergen

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