f2dc28f0b6
BZ: https://bugzilla.tianocore.org/show_bug.cgi?id=3275 An SEV-SNP guest requires that private memory (aka pages mapped encrypted) must be validated before being accessed. The validation process consist of the following sequence: 1) Set the memory encryption attribute in the page table (aka C-bit). Note: If the processor is in non-PAE mode, then all the memory accesses are considered private. 2) Add the memory range as private in the RMP table. This can be performed using the Page State Change VMGEXIT defined in the GHCB specification. 3) Use the PVALIDATE instruction to set the Validated Bit in the RMP table. During the guest creation time, the VMM encrypts the OVMF_CODE.fd using the SEV-SNP firmware provided LAUNCH_UPDATE_DATA command. In addition to encrypting the content, the command also validates the memory region. This allows us to execute the code without going through the validation sequence. During execution, the reset vector need to access some data pages (such as page tables, SevESWorkarea, Sec stack). The data pages are accessed as private memory. The data pages are not part of the OVMF_CODE.fd, so they were not validated during the guest creation. There are two approaches we can take to validate the data pages before the access: a) Enhance the OVMF reset vector code to validate the pages as described above (go through step 2 - 3). OR b) Validate the pages during the guest creation time. The SEV firmware provides a command which can be used by the VMM to validate the pages without affecting the measurement of the launch. Approach #b seems much simpler; it does not require any changes to the OVMF reset vector code. Update the OVMF metadata with the list of regions that must be pre-validated by the VMM before the boot. Cc: Michael Roth <michael.roth@amd.com> 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: Erdem Aktas <erdemaktas@google.com> Cc: Gerd Hoffmann <kraxel@redhat.com> Acked-by: Gerd Hoffmann <kraxel@redhat.com> Signed-off-by: Brijesh Singh <brijesh.singh@amd.com>
75 lines
2.1 KiB
NASM
75 lines
2.1 KiB
NASM
;-----------------------------------------------------------------------------
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; @file
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; OVMF metadata for the AMD SEV confidential computing guests
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;
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; Copyright (c) 2021, AMD Inc. All rights reserved.<BR>
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;
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; SPDX-License-Identifier: BSD-2-Clause-Patent
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;-----------------------------------------------------------------------------
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BITS 64
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%define OVMF_SEV_METADATA_VERSION 1
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; The section must be accepted or validated by the VMM before the boot
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%define OVMF_SECTION_TYPE_SNP_SEC_MEM 0x1
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; AMD SEV-SNP specific sections
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%define OVMF_SECTION_TYPE_SNP_SECRETS 0x2
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;
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; The section contains the hypervisor pre-populated CPUID values.
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; In the case of SEV-SNP, the CPUID values are filtered and measured by
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; the SEV-SNP firmware.
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; The CPUID format is documented in SEV-SNP firmware spec 0.9 section 7.1
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; (CPUID function structure).
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;
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%define OVMF_SECTION_TYPE_CPUID 0x3
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ALIGN 16
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TIMES (15 - ((OvmfSevGuidedStructureEnd - OvmfSevGuidedStructureStart + 15) % 16)) DB 0
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OvmfSevGuidedStructureStart:
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;
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; OvmfSev metadata descriptor
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;
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OvmfSevMetadataGuid:
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_DescriptorSev:
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DB 'A','S','E','V' ; Signature
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DD OvmfSevGuidedStructureEnd - _DescriptorSev ; Length
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DD OVMF_SEV_METADATA_VERSION ; Version
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DD (OvmfSevGuidedStructureEnd - _DescriptorSev - 16) / 12 ; Number of sections
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; Region need to be pre-validated by the hypervisor
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PreValidate1:
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DD SNP_SEC_MEM_BASE_DESC_1
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DD SNP_SEC_MEM_SIZE_DESC_1
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DD OVMF_SECTION_TYPE_SNP_SEC_MEM
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PreValidate2:
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DD SNP_SEC_MEM_BASE_DESC_2
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DD SNP_SEC_MEM_SIZE_DESC_2
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DD OVMF_SECTION_TYPE_SNP_SEC_MEM
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; SEV-SNP Secrets page
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SevSnpSecrets:
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DD SEV_SNP_SECRETS_BASE
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DD SEV_SNP_SECRETS_SIZE
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DD OVMF_SECTION_TYPE_SNP_SECRETS
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; CPUID values
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CpuidSec:
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DD CPUID_BASE
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DD CPUID_SIZE
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DD OVMF_SECTION_TYPE_CPUID
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; Region need to be pre-validated by the hypervisor
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PreValidate3:
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DD SNP_SEC_MEM_BASE_DESC_3
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DD SNP_SEC_MEM_SIZE_DESC_3
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DD OVMF_SECTION_TYPE_SNP_SEC_MEM
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OvmfSevGuidedStructureEnd:
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ALIGN 16
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