Re: [PATCH v2] arm64/efi: base UEFI mapping permissions on region attributes

[Will Deacon <will.deacon-5wv7dgnIgG8@public.gmane.org>]

Hi Ard,

On Wed, Aug 26, 2015 at 02:30:02PM +0100, Ard Biesheuvel wrote:
> Currently, we infer the UEFI memory region mapping permissions
> from the memory region type (i.e., runtime services code are
> mapped RWX and runtime services data mapped RW-). This appears to
> work fine but is not entirely UEFI spec compliant. So instead, use
> the designated permission attributes to decide how these regions
> should be mapped.
> 
> Since UEFIv2.5 introduces a new EFI_MEMORY_RO permission attribute,
> and redefines EFI_MEMORY_WP as a cacheability attribute, use only
> the former as a read-only attribute. For setting the PXN bit, the
> corresponding EFI_MEMORY_XP attribute is used.
> 
> Signed-off-by: Ard Biesheuvel <ard.biesheuvel-QSEj5FYQhm4dnm+yROfE0A@public.gmane.org>
> ---
> Changes since v1:
> - rewrote page size and alignment check to be more legible
> - use code that is STRICT_MM_TYPECHECKS compliant
> 
> Example output of a recent Tianocore build on FVP Foundation model
> is attached below.
> 
>  arch/arm64/kernel/efi.c | 37 +++++++++++++-------
>  1 file changed, 24 insertions(+), 13 deletions(-)
> 
> diff --git a/arch/arm64/kernel/efi.c b/arch/arm64/kernel/efi.c
> index ab21e0d58278..c8d587f46f3e 100644
> --- a/arch/arm64/kernel/efi.c
> +++ b/arch/arm64/kernel/efi.c
> @@ -235,7 +235,7 @@ static bool __init efi_virtmap_init(void)
>  
>  	for_each_efi_memory_desc(&memmap, md) {
>  		u64 paddr, npages, size;
> -		pgprot_t prot;
> +		pteval_t prot_val;
>  
>  		if (!(md->attribute & EFI_MEMORY_RUNTIME))
>  			continue;
> @@ -247,22 +247,33 @@ static bool __init efi_virtmap_init(void)
>  		memrange_efi_to_native(&paddr, &npages);
>  		size = npages << PAGE_SHIFT;
>  
> -		pr_info("  EFI remap 0x%016llx => %p\n",
> -			md->phys_addr, (void *)md->virt_addr);
> +		if (!is_normal_ram(md))
> +			prot_val = PROT_DEVICE_nGnRE;
> +		else
> +			prot_val = pgprot_val(PAGE_KERNEL_EXEC);
>  
>  		/*
> -		 * Only regions of type EFI_RUNTIME_SERVICES_CODE need to be
> -		 * executable, everything else can be mapped with the XN bits
> -		 * set.
> +		 * On 64 KB granule kernels, only use strict permissions when
> +		 * the region does not share a 64 KB page frame with another
> +		 * region at either end.
>  		 */
> -		if (!is_normal_ram(md))
> -			prot = __pgprot(PROT_DEVICE_nGnRE);
> -		else if (md->type == EFI_RUNTIME_SERVICES_CODE)
> -			prot = PAGE_KERNEL_EXEC;
> -		else
> -			prot = PAGE_KERNEL;
> +		if (PAGE_SIZE == EFI_PAGE_SIZE ||
> +		    (PAGE_ALIGNED(md->virt_addr) &&
> +		     PAGE_ALIGNED(md->phys_addr + md->num_pages * EFI_PAGE_SIZE))) {

Why do you use virt_addr instead of phys_addr for the base check?

Will