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

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Date:   Thu, 22 Sep 2016 12:46:59 -0500
From:   Tom Lendacky <thomas.lendacky@....com>
To:     Borislav Petkov <bp@...e.de>, Brijesh Singh <brijesh.singh@....com>
CC:     <simon.guinot@...uanux.org>, <linux-efi@...r.kernel.org>,
        <kvm@...r.kernel.org>, <rkrcmar@...hat.com>,
        <matt@...eblueprint.co.uk>, <linus.walleij@...aro.org>,
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        <davem@...emloft.net>
Subject: Re: [RFC PATCH v1 09/28] x86/efi: Access EFI data as encrypted when
 SEV is active

On 09/22/2016 09:35 AM, Borislav Petkov wrote:
> On Mon, Aug 22, 2016 at 07:25:25PM -0400, Brijesh Singh wrote:
>> From: Tom Lendacky <thomas.lendacky@....com>
>>
>> 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@....com>
>> ---
>>  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@tlendack-t1.amdoffice.net
> 
> but now here it is encrypted when SEV is enabled.
> 
> Do you mean, it is encrypted here because we're in the guest kernel?

Yes, the idea is that the SEV guest will be running encrypted from the
start, including the BIOS/UEFI, and so all of the EFI related data will
be encrypted.

Thanks,
Tom

> 
> Thanks.
>