Re: [PATCH 18/28] mm: enforce that vmap can't map pages executable

[Mark Rutland]

On Wed, Apr 08, 2020 at 01:59:16PM +0200, Christoph Hellwig wrote:
> To help enforcing the W^X protection don't allow remapping existing
> pages as executable.
> 
> Based on patch from Peter Zijlstra <peterz@xxxxxxxxxxxxx>.
> 
> Signed-off-by: Christoph Hellwig <hch@xxxxxx>
> ---
>  arch/x86/include/asm/pgtable_types.h | 6 ++++++
>  include/asm-generic/pgtable.h        | 4 ++++
>  mm/vmalloc.c                         | 2 +-
>  3 files changed, 11 insertions(+), 1 deletion(-)
> 
> diff --git a/arch/x86/include/asm/pgtable_types.h b/arch/x86/include/asm/pgtable_types.h
> index 947867f112ea..2e7c442cc618 100644
> --- a/arch/x86/include/asm/pgtable_types.h
> +++ b/arch/x86/include/asm/pgtable_types.h
> @@ -282,6 +282,12 @@ typedef struct pgprot { pgprotval_t pgprot; } pgprot_t;
>  
>  typedef struct { pgdval_t pgd; } pgd_t;
>  
> +static inline pgprot_t pgprot_nx(pgprot_t prot)
> +{
> +	return __pgprot(pgprot_val(prot) | _PAGE_NX);
> +}
> +#define pgprot_nx pgprot_nx
> +
>  #ifdef CONFIG_X86_PAE

I reckon for arm64 we can do similar in our <asm/pgtable.h>:

#define pgprot_nx(pgprot_t prot) \
	__pgprot_modify(prot, 0, PTE_PXN)

... matching the style of our existing pgprot_*() modifier helpers.

Mark.

>  
>  /*
> diff --git a/include/asm-generic/pgtable.h b/include/asm-generic/pgtable.h
> index 329b8c8ca703..8c5f9c29698b 100644
> --- a/include/asm-generic/pgtable.h
> +++ b/include/asm-generic/pgtable.h
> @@ -491,6 +491,10 @@ static inline int arch_unmap_one(struct mm_struct *mm,
>  #define flush_tlb_fix_spurious_fault(vma, address) flush_tlb_page(vma, address)
>  #endif
>  
> +#ifndef pgprot_nx
> +#define pgprot_nx(prot)	(prot)
> +#endif
> +
>  #ifndef pgprot_noncached
>  #define pgprot_noncached(prot)	(prot)
>  #endif
> diff --git a/mm/vmalloc.c b/mm/vmalloc.c
> index 7356b3f07bd8..334c75251ddb 100644
> --- a/mm/vmalloc.c
> +++ b/mm/vmalloc.c
> @@ -2390,7 +2390,7 @@ void *vmap(struct page **pages, unsigned int count,
>  	if (!area)
>  		return NULL;
>  
> -	if (map_kernel_range((unsigned long)area->addr, size, prot,
> +	if (map_kernel_range((unsigned long)area->addr, size, pgprot_nx(prot),
>  			pages) < 0) {
>  		vunmap(area->addr);
>  		return NULL;
> -- 
> 2.25.1
>