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

["Dov Murik" <dovmurik@linux.ibm.com>]

On 19/07/2021 18:57, Tom Lendacky wrote:
> 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.

It's a sad winking face... I'll fix.

Thanks,
-Dov


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