Re: [PATCH v3 4/4] x86: Split .init section to satisfy UEFI CA memory mitigation

[Marek Marczykowski-Górecki <marmarek@xxxxxxxxxxxxxxxxxxxxxx>]

On Tue, Jun 16, 2026 at 11:13:36AM +0100, Frediano Ziglio wrote:
> From: Frediano Ziglio <frediano.ziglio@xxxxxxxxx>
> 
> Currently .init section is both writeable and executable, split data and code
> to have 2 sections satisfying W^X rule.
> 
> It is a requirement for NX_COMPAT so the PE can be loaded with W^X perms
> in the pagetables.
> 
> NX_COMPAT is a requirement from shim-review,
> https://github.com/rhboot/shim-review#do-you-have-the-nx-bit-set-in-your-shim-if-so-is-your-entire-boot-stack-nx-compatible-and-what-testing-have-you-done-to-ensure-such-compatibility
> 
> Signed-off-by: Frediano Ziglio <frediano.ziglio@xxxxxxxxxx>

Acked-by: Marek Marczykowski-Górecki <marmarek@xxxxxxxxxxxxxxxxxxxxxx>

Is that the last piece necessary to satisfy the NX_COMPAT requirement? If
so, I suppose a subsequent patch should actually set the
IMAGE_DLLCHARACTERISTICS_NX_COMPAT bit (IIUC ld --nxcompat option), right?

> --
> Change since v1:
> - update comment style.
> ---
>  xen/arch/x86/xen.lds.S | 12 ++++--------
>  1 file changed, 4 insertions(+), 8 deletions(-)
> 
> diff --git a/xen/arch/x86/xen.lds.S b/xen/arch/x86/xen.lds.S
> index 749d9719cc..8fefda1816 100644
> --- a/xen/arch/x86/xen.lds.S
> +++ b/xen/arch/x86/xen.lds.S
> @@ -193,11 +193,7 @@ SECTIONS
>    __2M_init_start = .;         /* Start of 2M superpages, mapped RWX (boot 
> only). */
>    . = ALIGN(PAGE_SIZE);             /* Init code and data */
>    __init_begin = .;
> -#ifdef EFI /* EFI wants to merge all of .init.*  ELF doesn't. */
> -  DECL_SECTION(.init) {
> -#else
>    DECL_SECTION(.init.text) {
> -#endif
>         _sinittext = .;
>         *(.init.multiboot)
>         *(.init.text)
> @@ -210,12 +206,12 @@ SECTIONS
>          */
>         *(.altinstr_replacement)
>  
> -#ifdef EFI /* EFI wants to merge all of .init.*  ELF doesn't. */
> -       . = ALIGN(SMP_CACHE_BYTES);
> -#else
>    } PHDR(text)
> -  DECL_SECTION(.init.data) {
> +#ifdef EFI
> +  /* Align to satisfy UEFI CA memory mitigation. */
> +  . = ALIGN(SECTION_ALIGN);
>  #endif
> +  DECL_SECTION(.init.data) {
>         *(.init.bss.stack_aligned)
>         *(.init.data.page_aligned)
>  
> -- 
> 2.43.0
> 

-- 
Best Regards,
Marek Marczykowski-Górecki
Invisible Things Lab

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