Re: [edk2-devel] [PATCH v2 15/15] OvfmPkg/VmgExitLib: Validate #VC MMIO is to un-encrypted memory

["Lendacky, Thomas" <thomas.lendacky@amd.com>]

On 1/7/21 11:27 AM, Laszlo Ersek via groups.io wrote:
> On 01/06/21 22:21, Lendacky, Thomas wrote:
>> From: Tom Lendacky <thomas.lendacky@amd.com>
>>
>> BZ: https://nam11.safelinks.protection.outlook.com/?url=https%3A%2F%2Fbugzilla.tianocore.org%2Fshow_bug.cgi%3Fid%3D3108&amp;data=04%7C01%7Cthomas.lendacky%40amd.com%7Cbb067ba9ec7d47a785b108d8b33192f1%7C3dd8961fe4884e608e11a82d994e183d%7C0%7C0%7C637456372789618447%7CUnknown%7CTWFpbGZsb3d8eyJWIjoiMC4wLjAwMDAiLCJQIjoiV2luMzIiLCJBTiI6Ik1haWwiLCJXVCI6Mn0%3D%7C1000&amp;sdata=4gBvuWLwJxtPwahzl%2BjC6sNb%2FEgb0WmGscSwSdKBPOQ%3D&amp;reserved=0
>>
>> When SEV-ES is active, and MMIO operation will trigger a #VC and the
>> VmgExitLib exception handler will process this MMIO operation.
>>
>> A malicious hypervisor could try to extract information from encrypted
>> memory by setting a reserved bit in the guests nested page tables for
>> a non-MMIO area. This can result in the encrypted data being copied into
>> the GHCB shared buffer area and accessed by the hypervisor.
>>
>> Prevent this by ensuring that the MMIO source/destination is un-encrypted
>> memory. For the APIC register space, access is allowed in general.
>>
>> Cc: Jordan Justen <jordan.l.justen@intel.com>
>> Cc: Laszlo Ersek <lersek@redhat.com>
>> Cc: Ard Biesheuvel <ard.biesheuvel@arm.com>
>> Cc: Brijesh Singh <brijesh.singh@amd.com>
>> Acked-by: Laszlo Ersek <lersek@redhat.com>
>> Signed-off-by: Tom Lendacky <thomas.lendacky@amd.com>
>> ---
>>   OvmfPkg/AmdSev/AmdSevX64.dsc                                 |  1 +
>>   OvmfPkg/OvmfPkgX64.dsc                                       |  1 +
>>   OvmfPkg/Library/BaseMemEncryptSevLib/DxeMemEncryptSevLib.inf |  2 +-
>>   OvmfPkg/Library/VmgExitLib/SecVmgExitLib.inf                 |  2 +
>>   OvmfPkg/Library/VmgExitLib/VmgExitLib.inf                    |  2 +
>>   OvmfPkg/Library/VmgExitLib/VmgExitVcHandler.c                | 81 ++++++++++++++++++++
>>   6 files changed, 88 insertions(+), 1 deletion(-)
> 
> Looks OK, thanks.

Thanks for the review, Laszlo! I've applied all of your comments for this 
series should a v3 need to be submitted.

Thanks,
Tom

> Laszlo
>