Re: [PATCH v19 4/8] fork: Add shadow stack support to clone3()

["Edgecombe, Rick P" <rick.p.edgecombe@intel.com>]

On Tue, 2025-08-19 at 17:21 +0100, Mark Brown wrote:
> +int arch_shstk_validate_clone(struct task_struct *t,
> +			      struct vm_area_struct *vma,
> +			      struct page *page,
> +			      struct kernel_clone_args *args)
> +{
> +	/*
> +	 * SSP is aligned, so reserved bits and mode bit are a zero, just mark
> +	 * the token 64-bit.
> +	 */

What is this comment doing here? It doesn't make sense. It looks copied from
create_rstor_token()?

> +	void *maddr = page_address(page);
> +	unsigned long token;
> +	int offset;
> +	u64 expected;
> +
> +	token = args->shadow_stack_token;
> +	expected = (token + SS_FRAME_SIZE) | BIT(0);

Instead of the above comment, I think the important thing to say is that args-
>shadow_stack_token is 8 byte aligned, so offset can't overflow out of the page.

Maybe?

/* kernel_clone_args verification assures token address is 8 byte aligned */

> +	offset = offset_in_page(token);
> +
> +	if (!cmpxchg_to_user_page(vma, page, token, (unsigned long *)(maddr + offset),
> +				  expected, 0))
> +		return -EINVAL;
> +	set_page_dirty_lock(page);
> +
> +	return 0;
> +}
> +

With those changes, for the series:

Reviewed-by: Rick Edgecombe <rick.p.edgecombe@intel.com>