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     //
  81     // Read key length stored in big endian format
  82     //
  83     PublicKeyDataLength = SwapBytes32 (*(UINT32 *)(PublicKeyDataXdr));
  84     //
  85     // Point to the start of the key data
  86     //
  87     PublicKeyDataXdr += sizeof (UINT32);
  88     if (PublicKeyDataXdr + PublicKeyDataLength > PublicKeyDataXdrEnd) {
  89       //
  90       // Key data extends beyond end of PCD
  91       //
  92       break;
  93     }
  94
  95     //
  96     // Hash public key from PcdFmpDevicePkcs7CertBufferXdr using SHA256.
  97     // If error occurs computing SHA256, then assume test key is in use.
  98     //
  99     ZeroMem (Digest, SHA256_DIGEST_SIZE);
 100     if (!Sha256Init (HashContext)) {
 101       TestKeyUsed = TRUE;
 102       break;
 103     }
 104
 105     if (!Sha256Update (HashContext, PublicKeyDataXdr, PublicKeyDataLength)) {
 106       TestKeyUsed = TRUE;
 107       break;
 108     }
 109
 110     if (!Sha256Final (HashContext, Digest)) {
 111       TestKeyUsed = TRUE;
 112       break;
 113     }
 114
 115     //
 116     // Check if SHA256 hash of public key matches SHA256 hash of test key
 117     //
 118     if (CompareMem (Digest, PcdGetPtr (PcdFmpDeviceTestKeySha256Digest), SHA256_DIGEST_SIZE) == 0) {
 119       TestKeyUsed = TRUE;
 120       break;
 121     }
 122
 123     //
 124     // Point to start of next key
 125     //
 126     PublicKeyDataXdr += PublicKeyDataLength;
 127     PublicKeyDataXdr  = (UINT8 *)ALIGN_POINTER (PublicKeyDataXdr, sizeof (UINT32));
 128   }
 129
 130   //
 131   // Free hash context buffer required for SHA 256
 132   //
 133   if (HashContext != NULL) {
 134     FreePool (HashContext);
 135     HashContext = NULL;
 136   }
 137
 138   //
 139   // If test key detected or an error occurred checking for the test key, then
 140   // set PcdTestKeyUsed to TRUE.
 141   //
 142   if (TestKeyUsed) {
 143     DEBUG ((DEBUG_INFO, "FmpDxe(%s): Test key detected in PcdFmpDevicePkcs7CertBufferXdr.\n", mImageIdName));
 144     PcdSetBoolS (PcdTestKeyUsed, TRUE);
 145   } else {
 146     DEBUG ((DEBUG_INFO, "FmpDxe(%s): No test key detected in PcdFmpDevicePkcs7CertBufferXdr.\n", mImageIdName));
 147   }
 148 }