[PATCH] ARM: dma-mapping: don't allow DMA mappings to be marked executable

[linux@arm.linux.org.uk (Russell King - ARM Linux)]

On Thu, Oct 24, 2013 at 10:04:23AM +0100, Catalin Marinas wrote:
> Hi Russell,
> 
> On Thu, 2013-10-24 at 08:05 +0100, Russell King - ARM Linux wrote:
> > --- a/arch/arm/mm/dma-mapping.c
> > +++ b/arch/arm/mm/dma-mapping.c
> > @@ -688,7 +688,7 @@ static void *__dma_alloc(struct device *dev, size_t size, dma_addr_t *handle,
> >  void *arm_dma_alloc(struct device *dev, size_t size, dma_addr_t *handle,
> >  		    gfp_t gfp, struct dma_attrs *attrs)
> >  {
> > -	pgprot_t prot = __get_dma_pgprot(attrs, pgprot_kernel);
> > +	pgprot_t prot = __get_dma_pgprot(attrs, PAGE_KERNEL);
> 
> I think we lose the shareability attribute we add to pgprot_kernel when
> SMP. So this creates a mismatched aliases and could have implications on
> the barrier use (though I think we use the full system DSB in most cases
> related to DMA). But architecturally I would feel better if we have the
> same shareability domain.

We don't.

#define _MOD_PROT(p, b) __pgprot(pgprot_val(p) | (b))

#define PAGE_KERNEL             _MOD_PROT(pgprot_kernel, L_PTE_XN)
#define PAGE_KERNEL_EXEC        pgprot_kernel

PAGE_KERNEL is used in generic code to setup kernel mappings by things
like vmalloc() etc.