Re: [RFC PATCH v2 07/32] x86/efi: Access EFI data as encrypted when SEV is active

[Borislav Petkov]

On Thu, Mar 02, 2017 at 10:13:21AM -0500, Brijesh Singh wrote:
> From: Tom Lendacky <thomas.lendacky@xxxxxxx>
> 
> EFI data is encrypted when the kernel is run under SEV. Update the
> page table references to be sure the EFI memory areas are accessed
> encrypted.
> 
> Signed-off-by: Tom Lendacky <thomas.lendacky@xxxxxxx>
> Signed-off-by: Brijesh Singh <brijesh.singh@xxxxxxx>

This SOB chain looks good.

> ---
>  arch/x86/platform/efi/efi_64.c |   15 ++++++++++++++-
>  1 file changed, 14 insertions(+), 1 deletion(-)
> 
> diff --git a/arch/x86/platform/efi/efi_64.c b/arch/x86/platform/efi/efi_64.c
> index 2d8674d..9a76ed8 100644
> --- a/arch/x86/platform/efi/efi_64.c
> +++ b/arch/x86/platform/efi/efi_64.c
> @@ -45,6 +45,7 @@
>  #include <asm/realmode.h>
>  #include <asm/time.h>
>  #include <asm/pgalloc.h>
> +#include <asm/mem_encrypt.h>
>  
>  /*
>   * We allocate runtime services regions bottom-up, starting from -4G, i.e.
> @@ -286,7 +287,10 @@ int __init efi_setup_page_tables(unsigned long pa_memmap, unsigned num_pages)
>  	 * as trim_bios_range() will reserve the first page and isolate it away
>  	 * from memory allocators anyway.
>  	 */
> -	if (kernel_map_pages_in_pgd(pgd, 0x0, 0x0, 1, _PAGE_RW)) {
> +	pf = _PAGE_RW;
> +	if (sev_active())
> +		pf |= _PAGE_ENC;
> +	if (kernel_map_pages_in_pgd(pgd, 0x0, 0x0, 1, pf)) {
>  		pr_err("Failed to create 1:1 mapping for the first page!\n");
>  		return 1;
>  	}
> @@ -329,6 +333,9 @@ static void __init __map_region(efi_memory_desc_t *md, u64 va)
>  	if (!(md->attribute & EFI_MEMORY_WB))
>  		flags |= _PAGE_PCD;
>  
> +	if (sev_active())
> +		flags |= _PAGE_ENC;
> +

So I'm wondering if we could avoid this sprinkling of _PAGE_ENC in the
EFI code by defining something like __supported_pte_mask but called
__efi_base_page_flags or so which has _PAGE_ENC cleared in the SME case,
i.e., when baremetal and has it set in the SEV case.

Then we could simply OR in __efi_base_page_flags which the SME/SEV code
will set appropriately early enough.

Hmm.

Matt, what do you think?

-- 
Regards/Gruss,
    Boris.

SUSE Linux GmbH, GF: Felix ImendÃrffer, Jane Smithard, Graham Norton, HRB 21284 (AG NÃrnberg)
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