Re: [edk2-devel] [RFC PATCH 00/19] Add AMD Secure Nested Paging (SEV-SNP) support

["Laszlo Ersek" <lersek@redhat.com>]

Hi Brijesh,

On 03/24/21 16:31, Brijesh Singh wrote:
> BZ: https://bugzilla.tianocore.org/show_bug.cgi?id=3275
> 
> SEV-SNP builds upon existing SEV and SEV-ES functionality while adding
> new hardware-based memory protections. SEV-SNP adds strong memory integrity
> protection to help prevent malicious hypervisor-based attacks like data
> replay, memory re-mapping and more in order to create an isolated memory
> encryption environment.
>  
> This series provides the basic building blocks to support booting the SEV-SNP
> VMs, it does not cover all the security enhancement introduced by the SEV-SNP
> such as interrupt protection.
> 
> Many of the integrity guarantees of SEV-SNP are enforced through a new
> structure called the Reverse Map Table (RMP). Adding a new page to SEV-SNP
> VM requires a 2-step process. First, the hypervisor assigns a page to the
> guest using the new RMPUPDATE instruction. This transitions the page to
> guest-invalid. Second, the guest validates the page using the new PVALIDATE
> instruction. The SEV-SNP VMs can use the new "Page State Change Request NAE"
> defined in the GHCB specification to ask hypervisor to add or remove page
> from the RMP table.
>  
> Each page assigned to the SEV-SNP VM can either be validated or unvalidated,
> as indicated by the Validated flag in the page's RMP entry. There are two
> approaches that can be taken for the page validation: Pre-validation and
> Lazy Validation.
>   
> Under pre-validation, the pages are validated prior to first use. And under
> lazy validation, pages are validated when first accessed. An access to a
> unvalidated page results in a #VC exception, at which time the exception
> handler may validate the page. Lazy validation requires careful tracking of
> the validated pages to avoid validating the same GPA more than once. The
> recently introduced "Unaccepted" memory type can be used to communicate the
> unvalidated memory ranges to the Guest OS.
> 
> At this time we only support the pre-validation. OVMF detects all the available
> system RAM in the PEI phase. When SEV-SNP is enabled, the memory is validated
> before it is made available to the EDK2 core.

Can you describe this in a bit more detail, before I look at the
individual patches? Specifically, what existing logic in the PEI phase
was taken, and extended, and how?

If there is a particular patch whose commit message is closely related
to my question, can you point it out? Patch#15 perhaps? (Doesn't seem
like a big patch; for some reason I'd expect something more complex, but
perhaps that's only because it builds upon the many earlier patches.)

Thanks,
Laszlo

> 
> This series does not implements the following SEV-SNP features yet:
> 
> * CPUID filtering
> * AP bring up using the new SEV-SNP NAE
> * Lazy validation
> * Interrupt security
> 
> The series is based on commit:
> e542e05d4f UefiCpuPkg/SmmCpuFeaturesLib: Abstract PcdCpuMaxLogicalProcessorNumber
> 
> Additional resources
> ---------------------
> SEV-SNP whitepaper
> https://www.amd.com/system/files/TechDocs/SEV-SNP-strengthening-vm-isolation-with-integrity-protection-and-more.pdf
>  
> APM 2: https://www.amd.com/system/files/TechDocs/24593.pdf (section 15.36)
> 
> The complete source is available at
> https://github.com/AMDESE/ovmf/tree/sev-snp-rfc-1
> 
> GHCB spec v2:
>   The draft specification is posted on AMD-SEV-SNP mailing list:
>    https://lists.suse.com/mailman/private/amd-sev-snp/
> 
>   Copy of the spec is also available at 
>   https://github.com/AMDESE/AMDSEV/blob/sev-snp-devel/docs/56421-Guest_Hypervisor_Communication_Block_Standardization.pdf
> 
> GHCB spec v1:
> SEV-SNP firmware specification:
>  https://developer.amd.com/sev/
>   
> Cc: James Bottomley <jejb@linux.ibm.com>
> Cc: Min Xu <min.m.xu@intel.com>
> Cc: Jiewen Yao <jiewen.yao@intel.com>
> Cc: Tom Lendacky <thomas.lendacky@amd.com>
> Cc: Jordan Justen <jordan.l.justen@intel.com>
> Cc: Ard Biesheuvel <ardb+tianocore@kernel.org>
> Cc: Laszlo Ersek <lersek@redhat.com>
> 
> Brijesh Singh (19):
>   OvmfPkg: Reserve the Secrets and Cpuid page for the SEV-SNP guest
>   OvmfPkg: validate the data pages used in the SEC phase
>   MdePkg: Expand the SEV MSR to include the SNP definition
>   OvmfPkg/MemEncryptSevLib: add MemEncryptSevSnpEnabled()
>   MdePkg: Define the GHCB GPA structure
>   UefiCpuPkg/MpLib: add support to register GHCB GPA when SEV-SNP is
>     enabled
>   OvmfPkg: Add a library to support registering GHCB GPA
>   OvmfPkg: register GHCB gpa for the SEV-SNP guest
>   MdePkg: Add AsmPvalidate() support
>   OvmfPkg: Define the Page State Change VMGEXIT structures
>   OvmfPkg/ResetVector: Invalidate the GHCB page
>   OvmfPkg/MemEncryptSevLib: Add support to validate system RAM
>   OvmfPkg/SecMain: Validate the data/code pages used for the PEI phase
>   OvmfPkg/MemEncryptSevLib: Add support to validate RAM in PEI phase
>   OvmfPkg/PlatformPei: Validate the system RAM when SNP is active
>   OvmfPkg/MemEncryptSevLib: Add support to validate > 4GB memory in PEI
>     phase
>   OvmfPkg/VmgExitLib: Allow PMBASE register access in Dxe phase
>   OvmfPkg/MemEncryptSevLib: Validate the memory during set or clear enc
>     attribute
>   OvmfPkg/MemEncryptSevLib: Skip page state change for non RAM region
> 
>  MdePkg/Include/Library/BaseLib.h              |  37 +++
>  MdePkg/Include/Register/Amd/Fam17Msr.h        |  31 ++-
>  MdePkg/Include/Register/Amd/Ghcb.h            |  39 ++-
>  MdePkg/Library/BaseLib/BaseLib.inf            |   1 +
>  MdePkg/Library/BaseLib/X64/Pvalidate.nasm     |  43 +++
>  OvmfPkg/Include/Library/GhcbRegisterLib.h     |  27 ++
>  OvmfPkg/Include/Library/MemEncryptSevLib.h    |  30 +++
>  .../DxeMemEncryptSevLib.inf                   |   7 +
>  .../DxeMemEncryptSevLibInternal.c             |  27 ++
>  .../Ia32/SnpPageStateChange.c                 |  17 ++
>  .../PeiMemEncryptSevLib.inf                   |   9 +
>  .../PeiMemEncryptSevLibInternal.c             |  47 ++++
>  .../SecMemEncryptSevLib.inf                   |   4 +
>  .../SecMemEncryptSevLibInternal.c             |  39 +++
>  .../BaseMemEncryptSevLib/SnpPageStateChange.h |  37 +++
>  .../X64/PeiDxeSnpSetPageState.c               |  63 +++++
>  .../X64/PeiDxeVirtualMemory.c                 | 151 ++++++++++-
>  .../X64/PeiSnpSystemRamValidate.c             | 129 +++++++++
>  .../X64/SecSnpSystemRamValidate.c             |  23 ++
>  .../X64/SnpPageStateChangeInternal.c          | 254 ++++++++++++++++++
>  .../X64/SnpPageStateTrack.c                   | 119 ++++++++
>  .../X64/SnpPageStateTrack.h                   |  36 +++
>  .../X64/SnpSetPageState.h                     |  27 ++
>  .../BaseMemEncryptSevLib/X64/VirtualMemory.h  |  19 ++
>  .../Library/GhcbRegisterLib/GhcbRegisterLib.c |  97 +++++++
>  .../GhcbRegisterLib/GhcbRegisterLib.inf       |  33 +++
>  OvmfPkg/Library/VmgExitLib/SecVmgExitLib.inf  |   4 +
>  OvmfPkg/Library/VmgExitLib/VmgExitLib.inf     |   7 +
>  OvmfPkg/Library/VmgExitLib/VmgExitVcHandler.c |  45 ++++
>  OvmfPkg/OvmfPkg.dec                           |  12 +
>  OvmfPkg/OvmfPkgX64.dsc                        |   1 +
>  OvmfPkg/OvmfPkgX64.fdf                        |  33 ++-
>  OvmfPkg/PlatformPei/AmdSev.c                  |  52 ++++
>  OvmfPkg/PlatformPei/PlatformPei.inf           |   2 +
>  OvmfPkg/ResetVector/Ia16/ResetVectorVtf0.asm  |  24 ++
>  OvmfPkg/ResetVector/Ia32/PageTables64.asm     | 106 ++++++++
>  OvmfPkg/ResetVector/ResetVector.inf           |   5 +
>  OvmfPkg/ResetVector/ResetVector.nasmb         |   4 +
>  OvmfPkg/Sec/SecMain.c                         | 102 +++++++
>  OvmfPkg/Sec/SecMain.inf                       |   2 +
>  UefiCpuPkg/Library/MpInitLib/DxeMpInitLib.inf |   1 +
>  UefiCpuPkg/Library/MpInitLib/MpEqu.inc        |   1 +
>  UefiCpuPkg/Library/MpInitLib/MpLib.c          |   2 +
>  UefiCpuPkg/Library/MpInitLib/MpLib.h          |   2 +
>  UefiCpuPkg/Library/MpInitLib/PeiMpInitLib.inf |   1 +
>  UefiCpuPkg/Library/MpInitLib/X64/MpFuncs.nasm |  51 ++++
>  UefiCpuPkg/UefiCpuPkg.dec                     |   6 +
>  47 files changed, 1790 insertions(+), 19 deletions(-)
>  create mode 100644 MdePkg/Library/BaseLib/X64/Pvalidate.nasm
>  create mode 100644 OvmfPkg/Include/Library/GhcbRegisterLib.h
>  create mode 100644 OvmfPkg/Library/BaseMemEncryptSevLib/Ia32/SnpPageStateChange.c
>  create mode 100644 OvmfPkg/Library/BaseMemEncryptSevLib/SnpPageStateChange.h
>  create mode 100644 OvmfPkg/Library/BaseMemEncryptSevLib/X64/PeiDxeSnpSetPageState.c
>  create mode 100644 OvmfPkg/Library/BaseMemEncryptSevLib/X64/PeiSnpSystemRamValidate.c
>  create mode 100644 OvmfPkg/Library/BaseMemEncryptSevLib/X64/SecSnpSystemRamValidate.c
>  create mode 100644 OvmfPkg/Library/BaseMemEncryptSevLib/X64/SnpPageStateChangeInternal.c
>  create mode 100644 OvmfPkg/Library/BaseMemEncryptSevLib/X64/SnpPageStateTrack.c
>  create mode 100644 OvmfPkg/Library/BaseMemEncryptSevLib/X64/SnpPageStateTrack.h
>  create mode 100644 OvmfPkg/Library/BaseMemEncryptSevLib/X64/SnpSetPageState.h
>  create mode 100644 OvmfPkg/Library/GhcbRegisterLib/GhcbRegisterLib.c
>  create mode 100644 OvmfPkg/Library/GhcbRegisterLib/GhcbRegisterLib.inf
>