Re: [PATCH 06/16] x86/boot: Setup memory protection for bzImage code

[Andrew Cooper]

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.

> +	jnc	.Lnonx
> +
> +	movl	$1, (%rcx)

Your pointer has been clobbered with some feature flags.

movl $1, has_nx(%rip)

will work fine without needing the intermediary lea.

~Andrew