Re: [PATCH v3 6/6] mm/mprotect: use huge_ptep_get() for hugetlb

[Andrew Morton <akpm@linux-foundation.org>]

On Fri,  3 Jul 2026 11:41:59 +0000 Dev Jain <dev.jain@arm.com> wrote:

> prot_none_hugetlb_entry() is the hugetlb callback for the early
> mprotect(PROT_NONE) PFN permission walk on x86.
> 
> The callback passes the decoded PFN to pfn_modify_allowed(). For a
> hugetlb callback, the pte pointer refers to a hugetlb entry. On
> architectures where hugetlb entries need huge_ptep_get(), reading that
> entry with ptep_get() can make the permission check use the wrong PFN.
> 
> Use huge_ptep_get() before decoding the hugetlb PFN.
> 
> Currently there is no path which can trigger a bug: huge_ptep_get() is a
> simple ptep_get() for x86, and the prot_none walk occurs only for x86.
> 
> So no need to backport - use the correct helper anyways.
> 
> ...
>
> --- a/mm/mprotect.c
> +++ b/mm/mprotect.c
> @@ -699,14 +699,20 @@ static int prot_none_pte_entry(pte_t *pte, unsigned long addr,
>  		0 : -EACCES;
>  }
>  
> +#ifdef CONFIG_HUGETLB_PAGE
>  static int prot_none_hugetlb_entry(pte_t *pte, unsigned long hmask,
>  				   unsigned long addr, unsigned long next,
>  				   struct mm_walk *walk)
>  {
> -	return pfn_modify_allowed(pte_pfn(ptep_get(pte)),
> -				  *(pgprot_t *)(walk->private)) ?
> -		0 : -EACCES;
> +	const pte_t entry = huge_ptep_get(walk->mm, addr, pte);
> +
> +	if (pfn_modify_allowed(pte_pfn(entry), *(pgprot_t *)(walk->private)))
> +		return 0;
> +	return -EACCESS;

"EACCES".

>  }
> +#else
> +#define prot_none_hugetlb_entry	NULL
> +#endif

Presumably your .config resulted in this change not being tested...