Re: [PATCH 1/1] OvmfPkg/QemuFwCfgDxeLib: SEV: zero FW_CFG_DMA_ACCESS before decrypting it

[Laszlo Ersek <lersek@redhat.com>]

On 08/29/17 16:02, Brijesh Singh wrote:
> 
> 
> On 08/28/2017 07:39 AM, Laszlo Ersek wrote:
>> There's a small window between
>>
>> - AllocFwCfgDmaAccessBuffer() mapping the new FW_CFG_DMA_ACCESS object
>> for
>>    common buffer operation (i.e., decrypting it), and
>>
>> - InternalQemuFwCfgDmaBytes() setting the fields of the object.
>>
>> In this window, earlier garbage in the object is "leaked" to the
>> hypervisor. So zero the object before we decrypt it.
>>
>> (This commit message references AMD SEV directly, because QemuFwCfgDxeLib
>> is not *generally* enabled for IOMMU operation just yet, unlike our goal
>> for the virtio infrastructure. Instead, QemuFwCfgDxeLib uses
>> MemEncryptSevLib explicitly to detect SEV, and then relies on IOMMU
>> protocol behavior that is specific to SEV. At this point, this is by
>> design.)
>>
>> Cc: Brijesh Singh <brijesh.singh@amd.com>
>> Cc: Jordan Justen <jordan.l.justen@intel.com>
>> Cc: Tom Lendacky <thomas.lendacky@amd.com>
>> Contributed-under: TianoCore Contribution Agreement 1.1
>> Signed-off-by: Laszlo Ersek <lersek@redhat.com>
> 
> 
> Reviewed-by: Brijesh Singh <brijesh.singh@amd.com>

Thank you guys for the reviews, pushed as commit d431d8339e8b.

Laszlo