Re: [PATCH v2 17/39] mm: Fixup places that call pte_mkwrite() directly

[Peter Zijlstra]

On Thu, Sep 29, 2022 at 03:29:14PM -0700, Rick Edgecombe wrote:
> diff --git a/mm/userfaultfd.c b/mm/userfaultfd.c
> index 7327b2573f7c..b49372c7de41 100644
> --- a/mm/userfaultfd.c
> +++ b/mm/userfaultfd.c
> @@ -63,6 +63,7 @@ int mfill_atomic_install_pte(struct mm_struct *dst_mm, pmd_t *dst_pmd,
>  	int ret;
>  	pte_t _dst_pte, *dst_pte;
>  	bool writable = dst_vma->vm_flags & VM_WRITE;
> +	bool shstk = dst_vma->vm_flags & VM_SHADOW_STACK;
>  	bool vm_shared = dst_vma->vm_flags & VM_SHARED;
>  	bool page_in_cache = page->mapping;
>  	spinlock_t *ptl;
> @@ -83,9 +84,12 @@ int mfill_atomic_install_pte(struct mm_struct *dst_mm, pmd_t *dst_pmd,
>  		writable = false;
>  	}
>  
> -	if (writable)
> -		_dst_pte = pte_mkwrite(_dst_pte);
> -	else
> +	if (writable) {
> +		if (shstk)
> +			_dst_pte = pte_mkwrite_shstk(_dst_pte);
> +		else
> +			_dst_pte = pte_mkwrite(_dst_pte);
> +	} else
>  		/*
>  		 * We need this to make sure write bit removed; as mk_pte()
>  		 * could return a pte with write bit set.

Urgh.. that's unfortunate. But yeah, I don't see a way to make that
pretty either.