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OvmfPkg/AmdSev: add BlobVerifierLibSevHashes 

Add an implementation for BlobVerifierLib that locates the SEV hashes
table and verifies that the calculated hashes of the kernel, initrd, and
cmdline blobs indeed match the expected hashes stated in the hashes
table.

If there's a missing hash or a hash mismatch then EFI_ACCESS_DENIED is
returned which will cause a failure to load a kernel image.

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>
Reviewed-by: Jiewen Yao <jiewen.yao@intel.com>
[ardb: add CryptoPkg to accepted dependencies list for CI]
This commit is contained in:
Dov Murik 2021-07-01 13:19:46 +00:00 committed by mergify[bot]
parent 0deeab36d1
commit 385b9d80a0
3 changed files with 240 additions and 0 deletions
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37
OvmfPkg/AmdSev/BlobVerifierLibSevHashes/BlobVerifierLibSevHashes.inf Normal file
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@ -0,0 +1,37 @@
## @file
#
# Blob verifier library that uses SEV hashes table. The hashes table holds the
# allowed hashes of the kernel, initrd, and cmdline blobs.
#
# Copyright (C) 2021, IBM Corp
#
# SPDX-License-Identifier: BSD-2-Clause-Patent
#
##
[Defines]
INF_VERSION = 1.29
BASE_NAME = BlobVerifierLibSevHashes
FILE_GUID = 59e713b5-eff3-46a7-8d8b-46f4c004ad7b
MODULE_TYPE = BASE
VERSION_STRING = 1.0
LIBRARY_CLASS = BlobVerifierLib
CONSTRUCTOR = BlobVerifierLibSevHashesConstructor
[Sources]
BlobVerifierSevHashes.c
[Packages]
CryptoPkg/CryptoPkg.dec
MdePkg/MdePkg.dec
OvmfPkg/OvmfPkg.dec
[LibraryClasses]
BaseCryptLib
BaseMemoryLib
DebugLib
PcdLib
[FixedPcd]
gUefiOvmfPkgTokenSpaceGuid.PcdQemuHashTableBase
gUefiOvmfPkgTokenSpaceGuid.PcdQemuHashTableSize

202
OvmfPkg/AmdSev/BlobVerifierLibSevHashes/BlobVerifierSevHashes.c Normal file
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/** @file
Blob verifier library that uses SEV hashes table. The hashes table holds the
allowed hashes of the kernel, initrd, and cmdline blobs.
Copyright (C) 2021, IBM Corporation
SPDX-License-Identifier: BSD-2-Clause-Patent
**/
#include <Library/BaseCryptLib.h>
#include <Library/BaseLib.h>
#include <Library/BaseMemoryLib.h>
#include <Library/DebugLib.h>
#include <Library/BlobVerifierLib.h>
/**
The SEV Hashes table must be in encrypted memory and has the table
and its entries described by
<GUID>|UINT16 <len>|<data>
With the whole table GUID being 9438d606-4f22-4cc9-b479-a793d411fd21
The current possible table entries are for the kernel, the initrd
and the cmdline:
4de79437-abd2-427f-b835-d5b172d2045b kernel
44baf731-3a2f-4bd7-9af1-41e29169781d initrd
97d02dd8-bd20-4c94-aa78-e7714d36ab2a cmdline
The size of the entry is used to identify the hash, but the
expectation is that it will be 32 bytes of SHA-256.
**/
#define SEV_HASH_TABLE_GUID \
(GUID) { 0x9438d606, 0x4f22, 0x4cc9, { 0xb4, 0x79, 0xa7, 0x93, 0xd4, 0x11, 0xfd, 0x21 } }
#define SEV_KERNEL_HASH_GUID \
(GUID) { 0x4de79437, 0xabd2, 0x427f, { 0xb8, 0x35, 0xd5, 0xb1, 0x72, 0xd2, 0x04, 0x5b } }
#define SEV_INITRD_HASH_GUID \
(GUID) { 0x44baf731, 0x3a2f, 0x4bd7, { 0x9a, 0xf1, 0x41, 0xe2, 0x91, 0x69, 0x78, 0x1d } }
#define SEV_CMDLINE_HASH_GUID \
(GUID) { 0x97d02dd8, 0xbd20, 0x4c94, { 0xaa, 0x78, 0xe7, 0x71, 0x4d, 0x36, 0xab, 0x2a } }
STATIC CONST EFI_GUID mSevKernelHashGuid = SEV_KERNEL_HASH_GUID;
STATIC CONST EFI_GUID mSevInitrdHashGuid = SEV_INITRD_HASH_GUID;
STATIC CONST EFI_GUID mSevCmdlineHashGuid = SEV_CMDLINE_HASH_GUID;
#pragma pack (1)
typedef struct {
GUID Guid;
UINT16 Len;
UINT8 Data[];
} HASH_TABLE;
#pragma pack ()
STATIC HASH_TABLE *mHashesTable;
STATIC UINT16 mHashesTableSize;
STATIC
CONST GUID*
FindBlobEntryGuid (
IN CONST CHAR16 *BlobName
)
{
if (StrCmp (BlobName, L"kernel") == 0) {
return &mSevKernelHashGuid;
} else if (StrCmp (BlobName, L"initrd") == 0) {
return &mSevInitrdHashGuid;
} else if (StrCmp (BlobName, L"cmdline") == 0) {
return &mSevCmdlineHashGuid;
} else {
return NULL;
}
}
/**
Verify blob from an external source.
@param[in] BlobName The name of the blob
@param[in] Buf The data of the blob
@param[in] BufSize The size of the blob in bytes
@retval EFI_SUCCESS The blob was verified successfully.
@retval EFI_ACCESS_DENIED The blob could not be verified, and therefore
should be considered non-secure.
**/
EFI_STATUS
EFIAPI
VerifyBlob (
IN CONST CHAR16 *BlobName,
IN CONST VOID *Buf,
IN UINT32 BufSize
)
{
CONST GUID *Guid;
INT32 Remaining;
HASH_TABLE *Entry;
if (mHashesTable == NULL || mHashesTableSize == 0) {
DEBUG ((DEBUG_ERROR,
"%a: Verifier called but no hashes table discoverd in MEMFD\n",
__FUNCTION__));
return EFI_ACCESS_DENIED;
}
Guid = FindBlobEntryGuid (BlobName);
if (Guid == NULL) {
DEBUG ((DEBUG_ERROR, "%a: Unknown blob name \"%s\"\n", __FUNCTION__,
BlobName));
return EFI_ACCESS_DENIED;
}
//
// Remaining is INT32 to catch underflow in case Entry->Len has a
// very high UINT16 value
//
for (Entry = mHashesTable, Remaining = mHashesTableSize;
Remaining >= sizeof *Entry && Remaining >= Entry->Len;
Remaining -= Entry->Len,
Entry = (HASH_TABLE *)((UINT8 *)Entry + Entry->Len)) {
UINTN EntrySize;
EFI_STATUS Status;
UINT8 Hash[SHA256_DIGEST_SIZE];
if (!CompareGuid (&Entry->Guid, Guid)) {
continue;
}
DEBUG ((DEBUG_INFO, "%a: Found GUID %g in table\n", __FUNCTION__, Guid));
EntrySize = Entry->Len - sizeof Entry->Guid - sizeof Entry->Len;
if (EntrySize != SHA256_DIGEST_SIZE) {
DEBUG ((DEBUG_ERROR, "%a: Hash has the wrong size %d != %d\n",
__FUNCTION__, EntrySize, SHA256_DIGEST_SIZE));
return EFI_ACCESS_DENIED;
}
//
// Calculate the buffer's hash and verify that it is identical to the
// expected hash table entry
//
Sha256HashAll (Buf, BufSize, Hash);
if (CompareMem (Entry->Data, Hash, EntrySize) == 0) {
Status = EFI_SUCCESS;
DEBUG ((DEBUG_INFO, "%a: Hash comparison succeeded for \"%s\"\n",
__FUNCTION__, BlobName));
} else {
Status = EFI_ACCESS_DENIED;
DEBUG ((DEBUG_ERROR, "%a: Hash comparison failed for \"%s\"\n",
__FUNCTION__, BlobName));
}
return Status;
}
DEBUG ((DEBUG_ERROR, "%a: Hash GUID %g not found in table\n", __FUNCTION__,
Guid));
return EFI_ACCESS_DENIED;
}
/**
Locate the SEV hashes table.
This function always returns success, even if the table can't be found. The
subsequent VerifyBlob calls will fail if no table was found.
@retval RETURN_SUCCESS The hashes table is set up correctly, or there is no
hashes table
**/
RETURN_STATUS
EFIAPI
BlobVerifierLibSevHashesConstructor (
VOID
)
{
HASH_TABLE *Ptr;
UINT32 Size;
mHashesTable = NULL;
mHashesTableSize = 0;
Ptr = (void *)(UINTN)FixedPcdGet64 (PcdQemuHashTableBase);
Size = FixedPcdGet32 (PcdQemuHashTableSize);
if (Ptr == NULL || Size < sizeof *Ptr ||
!CompareGuid (&Ptr->Guid, &SEV_HASH_TABLE_GUID) ||
Ptr->Len < sizeof *Ptr || Ptr->Len > Size) {
return RETURN_SUCCESS;
}
DEBUG ((DEBUG_INFO, "%a: Found injected hashes table in secure location\n",
__FUNCTION__));
mHashesTable = (HASH_TABLE *)Ptr->Data;
mHashesTableSize = Ptr->Len - sizeof Ptr->Guid - sizeof Ptr->Len;
DEBUG ((DEBUG_VERBOSE, "%a: mHashesTable=0x%p, Size=%u\n", __FUNCTION__,
mHashesTable, mHashesTableSize));
return RETURN_SUCCESS;
}

1
OvmfPkg/OvmfPkg.ci.yaml
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@ -43,6 +43,7 @@
## options defined .pytool/Plugin/DependencyCheck
"DependencyCheck": {
"AcceptableDependencies": [
"CryptoPkg/CryptoPkg.dec",
"MdePkg/MdePkg.dec",
"MdeModulePkg/MdeModulePkg.dec",
"OvmfPkg/OvmfPkg.dec",