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

[Brijesh Singh <brijesh.singh@amd.com>]

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>