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SubjectRe: [PATCH 06/16] x86/boot: Setup memory protection for bzImage code
On 2022-10-19 10:57, Andrew Cooper wrote:
> On 06/09/2022 11:41, Evgeniy Baskov wrote:
>> diff --git a/arch/x86/boot/compressed/head_64.S
>> b/arch/x86/boot/compressed/head_64.S
>> index 5273367283b7..889ca7176aa7 100644
>> --- a/arch/x86/boot/compressed/head_64.S
>> +++ b/arch/x86/boot/compressed/head_64.S
>> @@ -602,6 +603,28 @@ SYM_FUNC_START_LOCAL_NOALIGN(.Lrelocated)
>> jmp *%rax
>> SYM_FUNC_END(.Lrelocated)
>>
>> +SYM_FUNC_START_LOCAL_NOALIGN(startup32_enable_nx_if_supported)
>> + pushq %rbx
>> +
>> + leaq has_nx(%rip), %rcx
>> +
>> + mov $0x80000001, %eax
>> + cpuid
>> + btl $20, %edx
>
> btl $(X86_FEATURE_NX & 31), %edx
>
> But also need to check for the availability of the extended leaf in the
> first place.

Yes, thank you for suggestion, that looks more readable. I will
also add the leaf node check. Is there any processor though that
supports long mode and does not support 0x80000001 leaf node?

>
>> + jnc .Lnonx
>> +
>> + movl $1, (%rcx)
>
> Your pointer has been clobbered with some feature flags.

Thanks, I apparently forgot to include fix for this into a patch set...

>
> movl $1, has_nx(%rip)
>
> will work fine without needing the intermediary lea.
>
> ~Andrew

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