Re: [PATCH v2 07/11] OvmfPkg/QemuKernelLoaderFsDxe: call VerifyBlob after fetch from fw_cfg

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

On 7/6/21 3:54 AM, Dov Murik wrote:
> In QemuKernelLoaderFsDxeEntrypoint we use FetchBlob to read the content
> of the kernel/initrd/cmdline from the QEMU fw_cfg interface.  Insert a
> call to VerifyBlob after fetching to allow BlobVerifierLib
> implementations to add a verification step for these blobs.
> 
> This will allow confidential computing OVMF builds to add verification
> mechanisms for these blobs that originate from an untrusted source
> (QEMU).
> 
> The null implementation of BlobVerifierLib does nothing in VerifyBlob,
> and therefore no functional change is expected.
> 
> Cc: Laszlo Ersek <lersek@redhat.com>
> Cc: Ard Biesheuvel <ardb+tianocore@kernel.org>
> Cc: Jordan Justen <jordan.l.justen@intel.com>
> Cc: Ashish Kalra <ashish.kalra@amd.com>
> Cc: Brijesh Singh <brijesh.singh@amd.com>
> Cc: Erdem Aktas <erdemaktas@google.com>
> Cc: James Bottomley <jejb@linux.ibm.com>
> Cc: Jiewen Yao <jiewen.yao@intel.com>
> Cc: Min Xu <min.m.xu@intel.com>
> Cc: Tom Lendacky <thomas.lendacky@amd.com>
> Ref: https://bugzilla.tianocore.org/show_bug.cgi?id=3457
> Co-developed-by: James Bottomley <jejb@linux.ibm.com>
> Signed-off-by: James Bottomley <jejb@linux.ibm.com>
> Signed-off-by: Dov Murik <dovmurik@linux.ibm.com>
> ---
>  OvmfPkg/QemuKernelLoaderFsDxe/QemuKernelLoaderFsDxe.c | 9 +++++++++
>  1 file changed, 9 insertions(+)
> 
> diff --git a/OvmfPkg/QemuKernelLoaderFsDxe/QemuKernelLoaderFsDxe.c b/OvmfPkg/QemuKernelLoaderFsDxe/QemuKernelLoaderFsDxe.c
> index c7ddd86f5c75..b43330d23b80 100644
> --- a/OvmfPkg/QemuKernelLoaderFsDxe/QemuKernelLoaderFsDxe.c
> +++ b/OvmfPkg/QemuKernelLoaderFsDxe/QemuKernelLoaderFsDxe.c
> @@ -17,6 +17,7 @@
>  #include <Guid/QemuKernelLoaderFsMedia.h>
>  #include <Library/BaseLib.h>
>  #include <Library/BaseMemoryLib.h>
> +#include <Library/BlobVerifierLib.h>
>  #include <Library/DebugLib.h>
>  #include <Library/DevicePathLib.h>
>  #include <Library/MemoryAllocationLib.h>
> @@ -1039,6 +1040,14 @@ QemuKernelLoaderFsDxeEntrypoint (
>      if (EFI_ERROR (Status)) {
>        goto FreeBlobs;
>      }
> +    Status = VerifyBlob (
> +               CurrentBlob->Name,
> +               CurrentBlob->Data,
> +               CurrentBlob->Size
> +             );

Just a nit, but the ");" should be under the "C" in CurrentBlob.

Thanks,
Tom

> +    if (EFI_ERROR (Status)) {
> +      goto FreeBlobs;
> +    }
>      mTotalBlobBytes += CurrentBlob->Size;
>    }
>    KernelBlob      = &mKernelBlob[KernelBlobTypeKernel];
>