Re: [edk2-devel] [PATCH 3/3] OvmfPkg/PlatformPei: Mark TPM MMIO range as unencrypted for SEV

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

On 4/22/21 9:51 AM, Tom Lendacky wrote:
> On 4/22/21 2:34 AM, Laszlo Ersek wrote:
>> On 04/21/21 01:13, Lendacky, Thomas wrote:
>>> On 4/20/21 5:54 PM, Lendacky, Thomas via groups.io wrote:
>>>> From: Tom Lendacky <thomas.lendacky@amd.com>
>>>>
>>>> BZ: https://nam11.safelinks.protection.outlook.com/?url=https%3A%2F%2Fbugzilla.tianocore.org%2Fshow_bug.cgi%3Fid%3D3345&amp;data=04%7C01%7Cthomas.lendacky%40amd.com%7C6b8da1f9a3bf4fb5f01e08d905613998%7C3dd8961fe4884e608e11a82d994e183d%7C0%7C0%7C637546737416495415%7CUnknown%7CTWFpbGZsb3d8eyJWIjoiMC4wLjAwMDAiLCJQIjoiV2luMzIiLCJBTiI6Ik1haWwiLCJXVCI6Mn0%3D%7C1000&amp;sdata=5vPlHPzGlS2%2Bqu3U4RPMITpyY%2F2ZxKJlaVYfFZItONQ%3D&amp;reserved=0
>>>>
>>>> The TPM support in OVMF performs MMIO accesses during the PEI phase. At
>>>> this point, MMIO ranges have not been marked un-encyrpted, so an SEV-ES
>>>> guest will fail attempting to perform MMIO to an encrypted address.
>>
>> (1) The subject says SEV, not SEV-ES, and the code in the patch too
>> suggests SEV, not SEV-ES. If that's correct, can you please update the
>> commit message?
> 
> Yes, I'll update the commit message. The action is correct for all SEV
> guests in general, but it is only with SEV-ES, where the tighter MMIO
> checks can be performed, that an actual issue shows up.
> 
>>
>>>>
>>>> Read the PcdTpmBaseAddress and mark the specification defined range
>>>> (0x5000 in length) as un-encrypted, to allow an SEV-ES guest to process
>>>> the MMIO requests.
>>>>
>>>> Cc: Laszlo Ersek <lersek@redhat.com>
>>>> Cc: Ard Biesheuvel <ardb+tianocore@kernel.org>
>>>> Cc: Jordan Justen <jordan.l.justen@intel.com>
>>>> Cc: Brijesh Singh <brijesh.singh@amd.com>
>>>> Cc: James Bottomley <jejb@linux.ibm.com>
>>>> Cc: Jiewen Yao <jiewen.yao@intel.com>
>>>> Cc: Min Xu <min.m.xu@intel.com>
>>>> Signed-off-by: Tom Lendacky <thomas.lendacky@amd.com>
>>>> ---
>>>>  OvmfPkg/PlatformPei/PlatformPei.inf |  1 +
>>>>  OvmfPkg/PlatformPei/AmdSev.c        | 19 +++++++++++++++++++
>>>>  2 files changed, 20 insertions(+)
>>>>
>>>> diff --git a/OvmfPkg/PlatformPei/PlatformPei.inf b/OvmfPkg/PlatformPei/PlatformPei.inf
>>>> index 6ef77ba7bb21..de60332e9390 100644
>>>> --- a/OvmfPkg/PlatformPei/PlatformPei.inf
>>>> +++ b/OvmfPkg/PlatformPei/PlatformPei.inf
>>>> @@ -113,6 +113,7 @@ [Pcd]
>>>>
>>>>  [FixedPcd]
>>>>    gEfiMdePkgTokenSpaceGuid.PcdPciExpressBaseAddress
>>>> +  gEfiSecurityPkgTokenSpaceGuid.PcdTpmBaseAddress
>>>>    gEmbeddedTokenSpaceGuid.PcdMemoryTypeEfiACPIMemoryNVS
>>>>    gEmbeddedTokenSpaceGuid.PcdMemoryTypeEfiACPIReclaimMemory
>>>>    gEmbeddedTokenSpaceGuid.PcdMemoryTypeEfiReservedMemoryType
>>>> diff --git a/OvmfPkg/PlatformPei/AmdSev.c b/OvmfPkg/PlatformPei/AmdSev.c
>>>> index dddffdebda4b..d524929f9e10 100644
>>>> --- a/OvmfPkg/PlatformPei/AmdSev.c
>>>> +++ b/OvmfPkg/PlatformPei/AmdSev.c
>>>> @@ -141,6 +141,7 @@ AmdSevInitialize (
>>>>    )
>>>>  {
>>>>    UINT64                            EncryptionMask;
>>>> +  UINT64                            TpmBaseAddress;
>>>>    RETURN_STATUS                     PcdStatus;
>>>>
>>>>    //
>>>> @@ -206,6 +207,24 @@ AmdSevInitialize (
>>>>      }
>>>>    }
>>>>
>>>> +  //
>>>> +  // PEI TPM support will perform MMIO accesses, be sure this range is not
>>>> +  // marked encrypted.
>>>> +  //
>>>> +  TpmBaseAddress = PcdGet64 (PcdTpmBaseAddress);
>>>> +  if (TpmBaseAddress != 0) {
>>>> +    RETURN_STATUS  DecryptStatus;
>>>> +
>>>> +    DecryptStatus = MemEncryptSevClearPageEncMask (
>>>> +                      0,
>>>> +                      TpmBaseAddress,
>>>> +                      EFI_SIZE_TO_PAGES (0x5000),
>>>> +                      FALSE
>>>> +                      );
>>>> +
>>>> +    ASSERT_RETURN_ERROR (DecryptStatus);
>>>> +  }
>>>> +
>>>
>>> Laszlo, I'm not sure if this is the best way to approach this. It is
>>> simple and straight forward and the TCG/TPM support is one of the few
>>> (only?) pieces of code that does actual MMIO during PEI that is bitten
>>> by not having the address marked as shared/unencrypted.
>>
>> In SEC, I think we have MMIO access too (LAPIC --
>> InitializeApicTimer()); why does that work?
>>
>> Hmm... Is that because we're immediately in x2apic mode, and that means
>> CPUID plus MSR accesses, and not MMIO? (I'm reminded of commit
>> decb365b0016 ("OvmfPkg: select LocalApicLib instance with x2apic
>> support", 2015-11-30).) And, we have #VC handling in SEC too.

Missed this question in my earlier reply...  LAPIC access has a dedicated
check in ValidateMmioMemory() to allow access in this case.

Thanks,
Tom

>>
>> Anyway: I think the TPM (MMIO) access you see comes from this PEIM:
>>
>>   OvmfPkg/Tcg/Tcg2Config/Tcg2ConfigPei.inf
>>
>> The driver uses the following library instance:
>>
>>   SecurityPkg/Library/Tpm2DeviceLibDTpm/Tpm2DeviceLibDTpm.inf
>>
>> This library instance is what depends on "PcdTpmBaseAddress".
>>
>> And it's not just that decrypting the TPM MMIO range in PlatformPei
>> "looks awkward", but I don't even see it immediately why PlatformPei is
>> guaranteed to be dispatched before Tcg2ConfigPei. The effective depex of
>> Tcg2ConfigPei is just "gEfiPeiPcdPpiGuid" (on X64), according to the
>> build report file. If Tcg2ConfigPei runs first, whatever we do in
>> PlatformPei is too late.
>>
>> I also don't like that, with this patch, we'd decrypt the TPM range even
>> if OVMF weren't built with "-D TPM_ENABLE". Namely, OVMF uses
>> "PcdTpmBaseAddress" as fixed (not dynamic), inheriting the nonzero
>> default from "SecurityPkg.dec". (In ArmVirtQemu, PcdTpmBaseAddress is
>> set dynamically, which is why Tcg2ConfigPei has an ARM-specific depex
>> too.)
>>
>>
>> (2) So, can you please try the following, in the
>> "OvmfPkg/Tcg/Tcg2Config/Tcg2ConfigPei.inf" module:
> 
> I'll take the input from each of your emails on this and see how that all
> works. Thanks for the insight and knowledge!
> 
> Tom
> 
>>
>>> diff --git a/OvmfPkg/Tcg/Tcg2Config/Tcg2ConfigPei.inf b/OvmfPkg/Tcg/Tcg2Config/Tcg2ConfigPei.inf
>>> index 6776ec931ce0..0d0572b83599 100644
>>> --- a/OvmfPkg/Tcg/Tcg2Config/Tcg2ConfigPei.inf
>>> +++ b/OvmfPkg/Tcg/Tcg2Config/Tcg2ConfigPei.inf
>>> @@ -20,13 +20,16 @@ [Defines]
>>>    ENTRY_POINT                    = Tcg2ConfigPeimEntryPoint
>>>
>>>  [Sources]
>>> +  MemEncrypt.h
>>>    Tcg2ConfigPeim.c
>>>    Tpm12Support.h
>>>
>>>  [Sources.IA32, Sources.X64]
>>> +  MemEncryptSev.c
>>>    Tpm12Support.c
>>>
>>>  [Sources.ARM, Sources.AARCH64]
>>> +  MemEncryptNull.c
>>>    Tpm12SupportNull.c
>>>
>>>  [Packages]
>>> @@ -43,6 +46,7 @@ [LibraryClasses]
>>>
>>>  [LibraryClasses.IA32, LibraryClasses.X64]
>>>    BaseLib
>>> +  MemEncryptSevLib
>>>    Tpm12DeviceLib
>>>
>>>  [Guids]
>>> @@ -56,6 +60,9 @@ [Ppis]
>>>  [Pcd]
>>>    gEfiSecurityPkgTokenSpaceGuid.PcdTpmInstanceGuid                 ## PRODUCES
>>>
>>> +[Pcd.IA32, Pcd.X64]
>>> +  gEfiSecurityPkgTokenSpaceGuid.PcdTpmBaseAddress         ## SOMETIMES_CONSUMES
>>> +
>>>  [Depex.IA32, Depex.X64]
>>>    TRUE
>>>
>>
>> In the "MemEncrypt.h" file, declare a function called
>> InternalTpmDecryptAddressRange(). The function definition in
>> "MemEncryptNull.c" should do nothing, while the one in "MemEncryptSev.c"
>> should check MemEncryptSevIsEnabled(), and then make the above-seen
>> MemEncryptSevClearPageEncMask() call.
>>
>> The new InternalTpmDecryptAddressRange() function should be called from
>> Tcg2ConfigPeimEntryPoint(), before the latter calls
>> InternalTpm12Detect(). Regarding error checking... if
>> InternalTpmDecryptAddressRange() fails, I think we can log an error
>> message, and hang with CpuDeadLoop().
>>
>> (An alternative approach would be to call MemEncryptSevIsEnabled() and
>> MemEncryptSevClearPageEncMask() regardless of architecture, i.e., also
>> on ARM / AARCH64. In addition to that, we'd have to implement a Null
>> instance of MemEncryptSevLib, and resolve MemEncryptSevLib to the Null
>> instance in the ArmVirtPkg DSC files. But I don't like that: the library
>> *class* carries SEV in the name, which is inherently X64-specific, thus
>> I wouldn't even like the lib *class* to leak into ArmVirtPkg.)
>>
>>
>> (3) If the approach in (2) works, then please don't forget to update the
>> patch subject (it currently refers to PlatformPei).
>>
>>
>> (4) The argument of the EFI_SIZE_TO_PAGES() function-like macro should
>> have type UINTN. The constant 0x5000 has type "int" (INT32); please cast
>> it to UINTN.
>>
>> (In fact I would prefer a new macro for 0x5000, somewhere in the
>> "MdePkg/Include/IndustryStandard/Tpm*.h" files; but I can see that
>> SecurityPkg already open-codes the 0x5000 constant in
>> "Tcg/Tcg2Acpi/Tpm.asl" and "Tcg/TcgSmm/Tpm.asl", so meh.)
>>
>> Thanks
>> Laszlo
>>