Re: [RFC Part1 PATCH v3 01/17] Documentation/x86: Add AMD Secure Encrypted Virtualization (SEV) descrption

Brijesh Singh
2017-07-25T14:59:21Z

On 07/25/2017 12:45 AM, Borislav Petkov wrote:
> On Mon, Jul 24, 2017 at 02:07:41PM -0500, Brijesh Singh wrote:
>
> Subject: Re: [RFC Part1 PATCH v3 01/17] Documentation/x86: Add AMD Secure Encrypted Virtualization (SEV) descrption
> ^^^^^^^^^^
>
> Please introduce a spellchecker into your workflow.
>
>> Update amd-memory-encryption document describing the AMD Secure Encrypted
>
> "Update the AMD memory encryption document...
>
> The patch has the proper URL already.
>
>> Virtualization (SEV) feature.
>>
>> Signed-off-by: Brijesh Singh <brijesh.singh-5C7GfCeVMHo@public.gmane.org>
>> ---
>> Documentation/x86/amd-memory-encryption.txt | 29 ++++++++++++++++++++++++++---
>> 1 file changed, 26 insertions(+), 3 deletions(-)
>>
>> diff --git a/Documentation/x86/amd-memory-encryption.txt b/Documentation/x86/amd-memory-encryption.txt
>> index f512ab7..747df07 100644
>> --- a/Documentation/x86/amd-memory-encryption.txt
>> +++ b/Documentation/x86/amd-memory-encryption.txt
>> @@ -1,4 +1,5 @@
>> -Secure Memory Encryption (SME) is a feature found on AMD processors.
>> +Secure Memory Encryption (SME) and Secure Encrypted Virtualization (SEV) are
>> +features found on AMD processors.
>>
>> SME provides the ability to mark individual pages of memory as encrypted using
>> the standard x86 page tables. A page that is marked encrypted will be
>> @@ -6,6 +7,12 @@ automatically decrypted when read from DRAM and encrypted when written to
>> DRAM. SME can therefore be used to protect the contents of DRAM from physical
>> attacks on the system.
>>
>> +SEV enables running encrypted virtual machine (VMs) in which the code and data
>
> machines
>
>> +of the virtual machine are secured so that decrypted version is available only
>
> ... of the guest VM ... ... so that a decrypted ...
>
>> +within the VM itself. SEV guest VMs have concept of private and shared memory.
>
> have *the* concept - you need to use
> definite and indefinite articles in your
> text.
>
>> +Private memory is encrypted with the guest-specific key, while shared memory
>> +may be encrypted with hypervisor key.
>
> And here you explain that the hypervisor key is the same key which we
> use in SME. So that people can make the connection.
>
>> +
>> A page is encrypted when a page table entry has the encryption bit set (see
>> below on how to determine its position). The encryption bit can also be
>> specified in the cr3 register, allowing the PGD table to be encrypted. Each
>> @@ -19,11 +26,20 @@ so that the PGD is encrypted, but not set the encryption bit in the PGD entry
>> for a PUD which results in the PUD pointed to by that entry to not be
>> encrypted.
>>
>> -Support for SME can be determined through the CPUID instruction. The CPUID
>> -function 0x8000001f reports information related to SME:
>> +When SEV is enabled, certain type of memory (namely insruction pages and guest
>
> When SEV is enabled, instruction pages and guest page tables are ...
>
>> +page tables) are always treated as private. Due to security reasons all DMA
>
> security reasons??
>
>> +operations inside the guest must be performed on shared memory. Since the
>> +memory encryption bit is only controllable by the guest OS when it is operating
>
> ... is controlled ...
>
>> +in 64-bit or 32-bit PAE mode, in all other modes the SEV hardware forces memory
>
> ... forces the memory ...
>
>> +encryption bit to 1.
>> +
>> +Support for SME and SEV can be determined through the CPUID instruction. The
>> +CPUID function 0x8000001f reports information related to SME:
>>
>> 0x8000001f[eax]:
>> Bit[0] indicates support for SME
>> + 0x800001f[eax]:
>
> There's a 0 missing and you don't really need it as it is already above.
>
>> + Bit[1] indicates support for SEV
>> 0x8000001f[ebx]:
>> Bits[5:0] pagetable bit number used to activate memory
>> encryption
>> @@ -39,6 +55,13 @@ determine if SME is enabled and/or to enable memory encryption:
>> Bit[23] 0 = memory encryption features are disabled
>> 1 = memory encryption features are enabled
>>
>> +If SEV is supported, MSR 0xc0010131 (MSR_F17H_SEV) can be used to determine if
>
> If this MSR is going to be part of the architecture - and I really think
> it is - then call it MSR_AMD64_SEV.
>

Thanks Boris, I'll update the doc per your feedbacks. And will rename the MSR to
MSR_AMD64_SEV.

-Brijesh