FmpDevicePkg/FmpDxe/DetectTestKey.c

   1 /** @file
   2   Detects if PcdFmpDevicePkcs7CertBufferXdr contains a test key.
   3
   4   Copyright (c) 2018 - 2019, Intel Corporation. All rights reserved.<BR>
   5
   6   SPDX-License-Identifier: BSD-2-Clause-Patent
   7
   8 **/
   9
  10 #include "FmpDxe.h"
  11
  12 /**
  13   Check to see if any of the keys in PcdFmpDevicePkcs7CertBufferXdr matches
  14   the test key.  PcdFmpDeviceTestKeySha256Digest contains the SHA256 hash of
  15   the test key.  For each key in PcdFmpDevicePkcs7CertBufferXdr, compute the
  16   SHA256 hash and compare it to PcdFmpDeviceTestKeySha256Digest.  If the
  17   SHA256 hash matches or there is then error computing the SHA256 hash, then
  18   set PcdTestKeyUsed to TRUE.  Skip this check if PcdTestKeyUsed is already
  19   TRUE or PcdFmpDeviceTestKeySha256Digest is not exactly SHA256_DIGEST_SIZE
  20   bytes.
  21 **/
  22 VOID
  23 DetectTestKey (
  24   VOID
  25   )
  26 {
  27   BOOLEAN  TestKeyUsed;
  28   UINTN    PublicKeyDataLength;
  29   UINT8    *PublicKeyDataXdr;
  30   UINT8    *PublicKeyDataXdrEnd;
  31   VOID     *HashContext;
  32   UINT8    Digest[SHA256_DIGEST_SIZE];
  33   UINTN    TestKeyDigestSize;
  34
  35   //
  36   // If PcdFmpDeviceTestKeySha256Digest is not exactly SHA256_DIGEST_SIZE bytes,
  37   // then skip the test key detection.
  38   //
  39   TestKeyDigestSize = PcdGetSize (PcdFmpDeviceTestKeySha256Digest);
  40   if (TestKeyDigestSize != SHA256_DIGEST_SIZE) {
  41     return;
  42   }
  43
  44   //
  45   // If PcdTestKeyUsed is already TRUE, then skip test key detection
  46   //
  47   TestKeyUsed = PcdGetBool (PcdTestKeyUsed);
  48   if (TestKeyUsed) {
  49     return;
  50   }
  51
  52   //
  53   // If PcdFmpDevicePkcs7CertBufferXdr is invalid, then skip test key detection
  54   //
  55   PublicKeyDataXdr    = PcdGetPtr (PcdFmpDevicePkcs7CertBufferXdr);
  56   PublicKeyDataXdrEnd = PublicKeyDataXdr + PcdGetSize (PcdFmpDevicePkcs7CertBufferXdr);
  57   if (PublicKeyDataXdr == NULL || PublicKeyDataXdr == PublicKeyDataXdrEnd) {
  58     return;
  59   }
  60
  61   //
  62   // Allocate hash context buffer required for SHA 256
  63   //
  64   HashContext = AllocatePool (Sha256GetContextSize ());
  65   if (HashContext == NULL) {
  66     TestKeyUsed = TRUE;
  67   }
  68
  69   //
  70   // Loop through all keys in PcdFmpDevicePkcs7CertBufferXdr
  71   //
  72   while (!TestKeyUsed && PublicKeyDataXdr < PublicKeyDataXdrEnd) {
  73     if (PublicKeyDataXdr + sizeof (UINT32) > PublicKeyDataXdrEnd) {
  74       //
  75       // Key data extends beyond end of PCD
  76       //
  77       break;
  78     }
  79     //
  80     // Read key length stored in big endian format
  81     //
  82     PublicKeyDataLength = SwapBytes32 (*(UINT32 *)(PublicKeyDataXdr));
  83     //
  84     // Point to the start of the key data
  85     //
  86     PublicKeyDataXdr += sizeof (UINT32);
  87     if (PublicKeyDataXdr + PublicKeyDataLength > PublicKeyDataXdrEnd) {
  88       //
  89       // Key data extends beyond end of PCD
  90       //
  91       break;
  92     }
  93
  94     //
  95     // Hash public key from PcdFmpDevicePkcs7CertBufferXdr using SHA256.
  96     // If error occurs computing SHA256, then assume test key is in use.
  97     //
  98     ZeroMem (Digest, SHA256_DIGEST_SIZE);
  99     if (!Sha256Init (HashContext)) {
 100       TestKeyUsed = TRUE;
 101       break;
 102     }
 103     if (!Sha256Update (HashContext, PublicKeyDataXdr, PublicKeyDataLength)) {
 104       TestKeyUsed = TRUE;
 105       break;
 106     }
 107     if (!Sha256Final (HashContext, Digest)) {
 108       TestKeyUsed = TRUE;
 109       break;
 110     }
 111
 112     //
 113     // Check if SHA256 hash of public key matches SHA256 hash of test key
 114     //
 115     if (CompareMem (Digest, PcdGetPtr (PcdFmpDeviceTestKeySha256Digest), SHA256_DIGEST_SIZE) == 0) {
 116       TestKeyUsed = TRUE;
 117       break;
 118     }
 119
 120     //
 121     // Point to start of next key
 122     //
 123     PublicKeyDataXdr += PublicKeyDataLength;
 124     PublicKeyDataXdr = (UINT8 *)ALIGN_POINTER (PublicKeyDataXdr, sizeof (UINT32));
 125   }
 126
 127   //
 128   // Free hash context buffer required for SHA 256
 129   //
 130   if (HashContext != NULL) {
 131     FreePool (HashContext);
 132     HashContext = NULL;
 133   }
 134
 135   //
 136   // If test key detected or an error occurred checking for the test key, then
 137   // set PcdTestKeyUsed to TRUE.
 138   //
 139   if (TestKeyUsed) {
 140     DEBUG ((DEBUG_INFO, "FmpDxe(%s): Test key detected in PcdFmpDevicePkcs7CertBufferXdr.\n", mImageIdName));
 141     PcdSetBoolS (PcdTestKeyUsed, TRUE);
 142   } else {
 143     DEBUG ((DEBUG_INFO, "FmpDxe(%s): No test key detected in PcdFmpDevicePkcs7CertBufferXdr.\n", mImageIdName));
 144   }
 145 }