Re: [PATCH v2 09/11] OvmfPkg/AmdSev: reserve MEMFD space for for firmware config hashes

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

On 7/6/21 3:54 AM, Dov Murik wrote:
> From: James Bottomley <jejb@linux.ibm.com>
> 
> Split the existing 4KB page reserved for SEV launch secrets into two
> parts: first 3KB for SEV launch secrets and last 1KB for firmware
> config hashes.
> 
> The area of the firmware config hashes will be attested (measured) by
> the PSP and thus the untrusted VMM can't pass in different files from
> what the guest owner allows.
> 
> Declare this in the Reset Vector table using GUID
> 7255371f-3a3b-4b04-927b-1da6efa8d454 and a uint32_t table of a base
> and size value (similar to the structure used to declare the launch
> secret block).
> 
> 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: Dov Murik <dovmurik@linux.ibm.com>
> Signed-off-by: Dov Murik <dovmurik@linux.ibm.com>
> Signed-off-by: James Bottomley <jejb@linux.ibm.com>

Reviewed by: Tom Lendacky <thomas.lendacky@amd.com>

> ---
>  OvmfPkg/OvmfPkg.dec                          |  6 ++++++
>  OvmfPkg/AmdSev/AmdSevX64.fdf                 |  5 ++++-
>  OvmfPkg/ResetVector/ResetVector.inf          |  2 ++
>  OvmfPkg/ResetVector/Ia16/ResetVectorVtf0.asm | 20 ++++++++++++++++++++
>  OvmfPkg/ResetVector/ResetVector.nasmb        |  2 ++
>  5 files changed, 34 insertions(+), 1 deletion(-)
> 
> diff --git a/OvmfPkg/OvmfPkg.dec b/OvmfPkg/OvmfPkg.dec
> index f82228d69cc2..2ab27f0c73c2 100644
> --- a/OvmfPkg/OvmfPkg.dec
> +++ b/OvmfPkg/OvmfPkg.dec
> @@ -324,6 +324,12 @@ [PcdsFixedAtBuild]
>    gUefiOvmfPkgTokenSpaceGuid.PcdSevLaunchSecretBase|0x0|UINT32|0x42
>    gUefiOvmfPkgTokenSpaceGuid.PcdSevLaunchSecretSize|0x0|UINT32|0x43
>  
> +  ## The base address and size of a hash table confirming allowed
> +  #  parameters to be passed in via the Qemu firmware configuration
> +  #  device
> +  gUefiOvmfPkgTokenSpaceGuid.PcdQemuHashTableBase|0x0|UINT32|0x47
> +  gUefiOvmfPkgTokenSpaceGuid.PcdQemuHashTableSize|0x0|UINT32|0x48
> +
>  [PcdsDynamic, PcdsDynamicEx]
>    gUefiOvmfPkgTokenSpaceGuid.PcdEmuVariableEvent|0|UINT64|2
>    gUefiOvmfPkgTokenSpaceGuid.PcdOvmfFlashVariablesEnable|FALSE|BOOLEAN|0x10
> diff --git a/OvmfPkg/AmdSev/AmdSevX64.fdf b/OvmfPkg/AmdSev/AmdSevX64.fdf
> index 9977b0f00a18..0a89749700c3 100644
> --- a/OvmfPkg/AmdSev/AmdSevX64.fdf
> +++ b/OvmfPkg/AmdSev/AmdSevX64.fdf
> @@ -59,9 +59,12 @@ [FD.MEMFD]
>  0x00B000|0x001000
>  gUefiCpuPkgTokenSpaceGuid.PcdSevEsWorkAreaBase|gUefiCpuPkgTokenSpaceGuid.PcdSevEsWorkAreaSize
>  
> -0x00C000|0x001000
> +0x00C000|0x000C00
>  gUefiOvmfPkgTokenSpaceGuid.PcdSevLaunchSecretBase|gUefiOvmfPkgTokenSpaceGuid.PcdSevLaunchSecretSize
>  
> +0x00CC00|0x000400
> +gUefiOvmfPkgTokenSpaceGuid.PcdQemuHashTableBase|gUefiOvmfPkgTokenSpaceGuid.PcdQemuHashTableSize
> +
>  0x00D000|0x001000
>  gUefiOvmfPkgTokenSpaceGuid.PcdOvmfSecGhcbBackupBase|gUefiOvmfPkgTokenSpaceGuid.PcdOvmfSecGhcbBackupSize
>  
> diff --git a/OvmfPkg/ResetVector/ResetVector.inf b/OvmfPkg/ResetVector/ResetVector.inf
> index dc38f68919cd..d028c92d8cfa 100644
> --- a/OvmfPkg/ResetVector/ResetVector.inf
> +++ b/OvmfPkg/ResetVector/ResetVector.inf
> @@ -47,3 +47,5 @@ [Pcd]
>  [FixedPcd]
>    gUefiOvmfPkgTokenSpaceGuid.PcdSevLaunchSecretBase
>    gUefiOvmfPkgTokenSpaceGuid.PcdSevLaunchSecretSize
> +  gUefiOvmfPkgTokenSpaceGuid.PcdQemuHashTableBase
> +  gUefiOvmfPkgTokenSpaceGuid.PcdQemuHashTableSize
> diff --git a/OvmfPkg/ResetVector/Ia16/ResetVectorVtf0.asm b/OvmfPkg/ResetVector/Ia16/ResetVectorVtf0.asm
> index 9c0b5853a46f..7ec3c6e980c3 100644
> --- a/OvmfPkg/ResetVector/Ia16/ResetVectorVtf0.asm
> +++ b/OvmfPkg/ResetVector/Ia16/ResetVectorVtf0.asm
> @@ -47,7 +47,27 @@ TIMES (15 - ((guidedStructureEnd - guidedStructureStart + 15) % 16)) DB 0
>  ;
>  guidedStructureStart:
>  
> +; SEV Hash Table Block
>  ;
> +; This describes the guest ram area where the hypervisor should
> +; install a table describing the hashes of certain firmware configuration
> +; device files that would otherwise be passed in unchecked.  The current
> +; use is for the kernel, initrd and command line values, but others may be
> +; added.  The data format is:
> +;
> +; base physical address (32 bit word)
> +; table length (32 bit word)
> +;
> +; GUID (SEV FW config hash block): 7255371f-3a3b-4b04-927b-1da6efa8d454
> +;
> +sevFwHashBlockStart:
> +    DD      SEV_FW_HASH_BLOCK_BASE
> +    DD      SEV_FW_HASH_BLOCK_SIZE
> +    DW      sevFwHashBlockEnd - sevFwHashBlockStart
> +    DB      0x1f, 0x37, 0x55, 0x72, 0x3b, 0x3a, 0x04, 0x4b
> +    DB      0x92, 0x7b, 0x1d, 0xa6, 0xef, 0xa8, 0xd4, 0x54
> +sevFwHashBlockEnd:
> +
>  ; SEV Secret block
>  ;
>  ; This describes the guest ram area where the hypervisor should
> diff --git a/OvmfPkg/ResetVector/ResetVector.nasmb b/OvmfPkg/ResetVector/ResetVector.nasmb
> index 5fbacaed5f9d..8d0bab02f8cb 100644
> --- a/OvmfPkg/ResetVector/ResetVector.nasmb
> +++ b/OvmfPkg/ResetVector/ResetVector.nasmb
> @@ -88,5 +88,7 @@
>    %define SEV_ES_AP_RESET_IP  FixedPcdGet32 (PcdSevEsWorkAreaBase)
>    %define SEV_LAUNCH_SECRET_BASE  FixedPcdGet32 (PcdSevLaunchSecretBase)
>    %define SEV_LAUNCH_SECRET_SIZE  FixedPcdGet32 (PcdSevLaunchSecretSize)
> +  %define SEV_FW_HASH_BLOCK_BASE  FixedPcdGet32 (PcdQemuHashTableBase)
> +  %define SEV_FW_HASH_BLOCK_SIZE  FixedPcdGet32 (PcdQemuHashTableSize)
>  %include "Ia16/ResetVectorVtf0.asm"
>  
>