FmpDevicePkg/FmpDxe/DetectTestKey.c

   1 /** @file
   2   Detects if PcdFmpDevicePkcs7CertBufferXdr contains a test key.
   3
   4   Copyright (c) 2018, Intel Corporation. All rights reserved.<BR>
   5
   6   SPDX-License-Identifier: BSD-2-Clause-Patent
   7
   8 **/
   9
  10 #include <PiDxe.h>
  11 #include <Library/DebugLib.h>
  12 #include <Library/BaseLib.h>
  13 #include <Library/BaseMemoryLib.h>
  14 #include <Library/PcdLib.h>
  15 #include <Library/MemoryAllocationLib.h>
  16 #include <Library/BaseCryptLib.h>
  17
  18 /**
  19   Check to see if any of the keys in PcdFmpDevicePkcs7CertBufferXdr matches
  20   the test key.  PcdFmpDeviceTestKeySha256Digest contains the SHA256 hash of
  21   the test key.  For each key in PcdFmpDevicePkcs7CertBufferXdr, compute the
  22   SHA256 hash and compare it to PcdFmpDeviceTestKeySha256Digest.  If the
  23   SHA256 hash matches or there is then error computing the SHA256 hash, then
  24   set PcdTestKeyUsed to TRUE.  Skip this check if PcdTestKeyUsed is already
  25   TRUE or PcdFmpDeviceTestKeySha256Digest is not exactly SHA256_DIGEST_SIZE
  26   bytes.
  27 **/
  28 VOID
  29 DetectTestKey (
  30   VOID
  31   )
  32 {
  33   BOOLEAN  TestKeyUsed;
  34   UINTN    PublicKeyDataLength;
  35   UINT8    *PublicKeyDataXdr;
  36   UINT8    *PublicKeyDataXdrEnd;
  37   VOID     *HashContext;
  38   UINT8    Digest[SHA256_DIGEST_SIZE];
  39   UINTN    TestKeyDigestSize;
  40
  41   //
  42   // If PcdFmpDeviceTestKeySha256Digest is not exacty SHA256_DIGEST_SIZE bytes,
  43   // then skip the test key detection.
  44   //
  45   TestKeyDigestSize = PcdGetSize (PcdFmpDeviceTestKeySha256Digest);
  46   if (TestKeyDigestSize != SHA256_DIGEST_SIZE) {
  47     return;
  48   }
  49
  50   //
  51   // If PcdTestKeyUsed is already TRUE, then skip test key detection
  52   //
  53   TestKeyUsed = PcdGetBool (PcdTestKeyUsed);
  54   if (TestKeyUsed) {
  55     return;
  56   }
  57
  58   //
  59   // If PcdFmpDevicePkcs7CertBufferXdr is invalid, then skip test key detection
  60   //
  61   PublicKeyDataXdr    = PcdGetPtr (PcdFmpDevicePkcs7CertBufferXdr);
  62   PublicKeyDataXdrEnd = PublicKeyDataXdr + PcdGetSize (PcdFmpDevicePkcs7CertBufferXdr);
  63   if (PublicKeyDataXdr == NULL || PublicKeyDataXdr == PublicKeyDataXdrEnd) {
  64     return;
  65   }
  66
  67   //
  68   // Allocate hash context buffer required for SHA 256
  69   //
  70   HashContext = AllocatePool (Sha256GetContextSize ());
  71   if (HashContext == NULL) {
  72     TestKeyUsed = TRUE;
  73   }
  74
  75   //
  76   // Loop through all keys in PcdFmpDevicePkcs7CertBufferXdr
  77   //
  78   while (!TestKeyUsed && PublicKeyDataXdr < PublicKeyDataXdrEnd) {
  79     if (PublicKeyDataXdr + sizeof (UINT32) > PublicKeyDataXdrEnd) {
  80       //
  81       // Key data extends beyond end of PCD
  82       //
  83       break;
  84     }
  85     //
  86     // Read key length stored in big endian format
  87     //
  88     PublicKeyDataLength = SwapBytes32 (*(UINT32 *)(PublicKeyDataXdr));
  89     //
  90     // Point to the start of the key data
  91     //
  92     PublicKeyDataXdr += sizeof (UINT32);
  93     if (PublicKeyDataXdr + PublicKeyDataLength > PublicKeyDataXdrEnd) {
  94       //
  95       // Key data extends beyond end of PCD
  96       //
  97       break;
  98     }
  99
 100     //
 101     // Hash public key from PcdFmpDevicePkcs7CertBufferXdr using SHA256.
 102     // If error occurs computing SHA256, then assume test key is in use.
 103     //
 104     ZeroMem (Digest, SHA256_DIGEST_SIZE);
 105     if (!Sha256Init (HashContext)) {
 106       TestKeyUsed = TRUE;
 107       break;
 108     }
 109     if (!Sha256Update (HashContext, PublicKeyDataXdr, PublicKeyDataLength)) {
 110       TestKeyUsed = TRUE;
 111       break;
 112     }
 113     if (!Sha256Final (HashContext, Digest)) {
 114       TestKeyUsed = TRUE;
 115       break;
 116     }
 117
 118     //
 119     // Check if SHA256 hash of public key matches SHA256 hash of test key
 120     //
 121     if (CompareMem (Digest, PcdGetPtr (PcdFmpDeviceTestKeySha256Digest), SHA256_DIGEST_SIZE) == 0) {
 122       TestKeyUsed = TRUE;
 123       break;
 124     }
 125
 126     //
 127     // Point to start of next key
 128     //
 129     PublicKeyDataXdr += PublicKeyDataLength;
 130     PublicKeyDataXdr = (UINT8 *)ALIGN_POINTER (PublicKeyDataXdr, sizeof (UINT32));
 131   }
 132
 133   //
 134   // Free hash context buffer required for SHA 256
 135   //
 136   if (HashContext != NULL) {
 137     FreePool (HashContext);
 138     HashContext = NULL;
 139   }
 140
 141   //
 142   // If test key detected or an error occured checking for the test key, then
 143   // set PcdTestKeyUsed to TRUE.
 144   //
 145   if (TestKeyUsed) {
 146     DEBUG ((DEBUG_INFO, "FmpDxe: Test key detected in PcdFmpDevicePkcs7CertBufferXdr.\n"));
 147     PcdSetBoolS (PcdTestKeyUsed, TRUE);
 148   } else {
 149     DEBUG ((DEBUG_INFO, "FmpDxe: No test key detected in PcdFmpDevicePkcs7CertBufferXdr.\n"));
 150   }
 151 }