Re: [RFC PATCH v1 09/28] x86/efi: Access EFI data as encrypted when SEV is active

[Borislav Petkov]

On Mon, Aug 22, 2016 at 07:25:25PM -0400, 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>
> ---
>  arch/x86/platform/efi/efi_64.c |   14 ++++++++++++--
>  1 file changed, 12 insertions(+), 2 deletions(-)
> 
> diff --git a/arch/x86/platform/efi/efi_64.c b/arch/x86/platform/efi/efi_64.c
> index 0871ea4..98363f3 100644
> --- a/arch/x86/platform/efi/efi_64.c
> +++ b/arch/x86/platform/efi/efi_64.c
> @@ -213,7 +213,7 @@ void efi_sync_low_kernel_mappings(void)
>  
>  int __init efi_setup_page_tables(unsigned long pa_memmap, unsigned num_pages)
>  {
> -	unsigned long pfn, text;
> +	unsigned long pfn, text, flags;
>  	efi_memory_desc_t *md;
>  	struct page *page;
>  	unsigned npages;
> @@ -230,6 +230,10 @@ int __init efi_setup_page_tables(unsigned long pa_memmap, unsigned num_pages)
>  	efi_scratch.efi_pgt = (pgd_t *)__sme_pa(efi_pgd);
>  	pgd = efi_pgd;
>  
> +	flags = _PAGE_NX | _PAGE_RW;
> +	if (sev_active)
> +		flags |= _PAGE_ENC;

So this is confusing me. There's this patch which says EFI data is
accessed in the clear:

https://lkml.kernel.org/r/20160822223738.29880.6909.stgit@xxxxxxxxxxxxxxxxxxxxxxxxx

but now here it is encrypted when SEV is enabled.

Do you mean, it is encrypted here because we're in the guest kernel?

Thanks.

-- 
Regards/Gruss,
    Boris.

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