VBoot Reference: Refactor Pass 1: Split {firmware|kernel}_image

src/platform/vboot_reference/utils/kernel_image_fw.c

+/* Copyright (c) 2010 The Chromium OS Authors. All rights reserved.
+ * Use of this source code is governed by a BSD-style license that can be
+ * found in the LICENSE file.
+ *
+ * Functions for verifying a verified boot kernel image.
+ * (Firmware portion)
+ */
+
+#include "kernel_image_fw.h"
+
+#include "padding.h"
+#include "rollback_index.h"
+#include "rsa_utility.h"
+#include "sha_utility.h"
+#include "utility.h"
+
+/* Macro to determine the size of a field structure in the KernelImage
+ * structure. */
+#define FIELD_LEN(field) (sizeof(((KernelImage*)0)->field))
+#define KERNEL_CONFIG_FIELD_LEN (FIELD_LEN(kernel_version) + FIELD_LEN(options.version) + \
+                                 FIELD_LEN(options.cmd_line) + \
+                                 FIELD_LEN(options.kernel_len) + \
+                                 FIELD_LEN(options.kernel_load_addr) + \
+                                 FIELD_LEN(options.kernel_entry_addr))
+
+char* kVerifyKernelErrors[VERIFY_KERNEL_MAX] = {
+  "Success.",
+  "Invalid Image.",
+  "Kernel Key Signature Failed.",
+  "Invalid Kernel Verification Algorithm.",
+  "Config Signature Failed.",
+  "Kernel Signature Failed.",
+  "Wrong Kernel Magic.",
+};
+
+int VerifyKernelHeader(const uint8_t* firmware_key_blob,
+                       const uint8_t* header_blob,
+                       const int dev_mode,
+                       int* firmware_algorithm,
+                       int* kernel_algorithm,
+                       int* kernel_header_len) {
+  int kernel_sign_key_len;
+  int firmware_sign_key_len;
+  uint16_t header_version, header_len;
+  uint16_t firmware_sign_algorithm, kernel_sign_algorithm;
+  uint8_t* header_checksum = NULL;
+
+  /* Base Offset for the header_checksum field. Actual offset is
+   * this + kernel_sign_key_len. */
+  int base_header_checksum_offset = (FIELD_LEN(header_version) +
+                                     FIELD_LEN(header_len) +
+                                     FIELD_LEN(firmware_sign_algorithm) +
+                                     FIELD_LEN(kernel_sign_algorithm) +
+                                     FIELD_LEN(kernel_key_version));
+
+  Memcpy(&header_version, header_blob, sizeof(header_version));
+  Memcpy(&header_len, header_blob + FIELD_LEN(header_version),
+         sizeof(header_len));
+  Memcpy(&firmware_sign_algorithm,
+         header_blob + (FIELD_LEN(header_version) +
+                        FIELD_LEN(header_len)),
+         sizeof(firmware_sign_algorithm));
+  Memcpy(&kernel_sign_algorithm,
+         header_blob + (FIELD_LEN(header_version) +
+                        FIELD_LEN(header_len) +
+                        FIELD_LEN(firmware_sign_algorithm)),
+         sizeof(kernel_sign_algorithm));
+
+  /* TODO(gauravsh): Make this return two different error types depending
+   * on whether the firmware or kernel signing algorithm is invalid. */
+  if (firmware_sign_algorithm >= kNumAlgorithms)
+    return VERIFY_KERNEL_INVALID_ALGORITHM;
+  if (kernel_sign_algorithm >= kNumAlgorithms)
+    return VERIFY_KERNEL_INVALID_ALGORITHM;
+
+  *firmware_algorithm = (int) firmware_sign_algorithm;
+  *kernel_algorithm = (int) kernel_sign_algorithm;
+  kernel_sign_key_len = RSAProcessedKeySize(kernel_sign_algorithm);
+  firmware_sign_key_len = RSAProcessedKeySize(firmware_sign_algorithm);
+
+
+  /* Verify if header len is correct? */
+  if (header_len != (base_header_checksum_offset +
+                     kernel_sign_key_len +
+                     FIELD_LEN(header_checksum))) {
+    debug("VerifyKernelHeader: Header length mismatch\n");
+    return VERIFY_KERNEL_INVALID_IMAGE;
+  }
+  *kernel_header_len = (int) header_len;
+
+  /* Verify if the hash of the header is correct. */
+  header_checksum = DigestBuf(header_blob,
+                              header_len - FIELD_LEN(header_checksum),
+                              SHA512_DIGEST_ALGORITHM);
+  if (SafeMemcmp(header_checksum,
+                 header_blob + (base_header_checksum_offset +
+                                kernel_sign_key_len),
+                 FIELD_LEN(header_checksum))) {
+    Free(header_checksum);
+    debug("VerifyKernelHeader: Invalid header hash\n");
+    return VERIFY_KERNEL_INVALID_IMAGE;
+  }
+  Free(header_checksum);
+
+  /* Verify kernel key signature unless we are in dev mode. */
+  if (!dev_mode) {
+    if (!RSAVerifyBinary_f(firmware_key_blob, NULL,  /* Key to use */
+                           header_blob,  /* Data to verify */
+                           header_len, /* Length of data */
+                           header_blob + header_len,  /* Expected Signature */
+                           firmware_sign_algorithm))
+      return VERIFY_KERNEL_KEY_SIGNATURE_FAILED;
+  }
+  return 0;
+}
+
+int VerifyKernelConfig(RSAPublicKey* kernel_sign_key,
+                       const uint8_t* config_blob,
+                       int algorithm,
+                       uint64_t* kernel_len) {
+  uint64_t len;
+  if (!RSAVerifyBinary_f(NULL, kernel_sign_key,  /* Key to use */
+                         config_blob,  /* Data to verify */
+                         KERNEL_CONFIG_FIELD_LEN,  /* Length of data */
+                         config_blob + KERNEL_CONFIG_FIELD_LEN,  /* Expected
+                                                                  * Signature */
+                         algorithm))
+    return VERIFY_KERNEL_CONFIG_SIGNATURE_FAILED;
+
+  Memcpy(&len,
+         config_blob + (FIELD_LEN(kernel_version) + FIELD_LEN(options.version) +
+                              FIELD_LEN(options.cmd_line)),
+         sizeof(len));
+  *kernel_len = len;
+  return 0;
+}
+
+int VerifyKernelData(RSAPublicKey* kernel_sign_key,
+                     const uint8_t* kernel_config_start,
+                     const uint8_t* kernel_data_start,
+                     uint64_t kernel_len,
+                     int algorithm) {
+  int signature_len = siglen_map[algorithm];
+  uint8_t* digest;
+  DigestContext ctx;
+
+  /* Since the kernel signature is computed over the kernel version, options
+   * and data, which does not form a contiguous region of memory, we calculate
+   * the message digest ourselves. */
+  DigestInit(&ctx, algorithm);
+  DigestUpdate(&ctx, kernel_config_start, KERNEL_CONFIG_FIELD_LEN);
+  DigestUpdate(&ctx, kernel_data_start + signature_len, kernel_len);
+  digest = DigestFinal(&ctx);
+  if (!RSAVerifyBinaryWithDigest_f(
+          NULL, kernel_sign_key,  /* Key to use. */
+          digest, /* Digest of the data to verify. */
+          kernel_data_start,  /* Expected Signature */
+          algorithm)) {
+    Free(digest);
+    return VERIFY_KERNEL_SIGNATURE_FAILED;
+  }
+  Free(digest);
+  return 0;
+}
+
+int VerifyKernel(const uint8_t* firmware_key_blob,
+                 const uint8_t* kernel_blob,
+                 const int dev_mode) {
+  int error_code;
+  int firmware_sign_algorithm;  /* Firmware signing key algorithm. */
+  int kernel_sign_algorithm;  /* Kernel Signing key algorithm. */
+  RSAPublicKey* kernel_sign_key;
+  int kernel_sign_key_len, kernel_key_signature_len, kernel_signature_len,
+      header_len;
+  uint64_t kernel_len;
+  const uint8_t* header_ptr;  /* Pointer to header. */
+  const uint8_t* kernel_sign_key_ptr;  /* Pointer to signing key. */
+  const uint8_t* config_ptr;  /* Pointer to kernel config block. */
+  const uint8_t* kernel_ptr;  /* Pointer to kernel signature/data. */
+
+  /* Note: All the offset calculations are based on struct FirmwareImage which
+   * is defined in include/firmware_image.h. */
+
+  /* Compare magic bytes. */
+  if (SafeMemcmp(kernel_blob, KERNEL_MAGIC, KERNEL_MAGIC_SIZE))
+    return VERIFY_KERNEL_WRONG_MAGIC;
+  header_ptr = kernel_blob + KERNEL_MAGIC_SIZE;
+
+  /* Only continue if header verification succeeds. */
+  if ((error_code = VerifyKernelHeader(firmware_key_blob, header_ptr, dev_mode,
+                                       &firmware_sign_algorithm,
+                                       &kernel_sign_algorithm, &header_len))) {
+    debug("VerifyKernel: Kernel header verification failed.\n");
+    return error_code;  /* AKA jump to recovery. */
+  }
+  /* Parse signing key into RSAPublicKey structure since it is required multiple
+   * times. */
+  kernel_sign_key_len = RSAProcessedKeySize(kernel_sign_algorithm);
+  kernel_sign_key_ptr = header_ptr + (FIELD_LEN(header_version) +
+                                      FIELD_LEN(header_len) +
+                                      FIELD_LEN(firmware_sign_algorithm) +
+                                      FIELD_LEN(kernel_sign_algorithm) +
+                                      FIELD_LEN(kernel_key_version));
+  kernel_sign_key = RSAPublicKeyFromBuf(kernel_sign_key_ptr,
+                                        kernel_sign_key_len);
+  kernel_signature_len = siglen_map[kernel_sign_algorithm];
+  kernel_key_signature_len = siglen_map[firmware_sign_algorithm];
+
+  /* Only continue if config verification succeeds. */
+  config_ptr = (header_ptr + header_len + kernel_key_signature_len);
+  if ((error_code = VerifyKernelConfig(kernel_sign_key, config_ptr,
+                                       kernel_sign_algorithm,
+                                       &kernel_len))) {
+    RSAPublicKeyFree(kernel_sign_key);
+    return error_code;  /* AKA jump to recovery. */
+  }
+  /* Only continue if kernel data verification succeeds. */
+  kernel_ptr = (config_ptr +
+                KERNEL_CONFIG_FIELD_LEN +  /* Skip config block/signature. */
+                kernel_signature_len);
+
+  if ((error_code = VerifyKernelData(kernel_sign_key, config_ptr, kernel_ptr,
+                                     kernel_len,
+                                     kernel_sign_algorithm))) {
+    RSAPublicKeyFree(kernel_sign_key);
+    return error_code;  /* AKA jump to recovery. */
+  }
+  RSAPublicKeyFree(kernel_sign_key);
+  return 0;  /* Success! */
+}
+
+uint32_t GetLogicalKernelVersion(uint8_t* kernel_blob) {
+  uint8_t* kernel_ptr;
+  uint16_t kernel_key_version;
+  uint16_t kernel_version;
+  uint16_t firmware_sign_algorithm;
+  uint16_t kernel_sign_algorithm;
+  int kernel_key_signature_len;
+  int kernel_sign_key_len;
+  kernel_ptr = kernel_blob + (FIELD_LEN(magic) +
+                              FIELD_LEN(header_version) +
+                              FIELD_LEN(header_len));
+  Memcpy(&firmware_sign_algorithm, kernel_ptr, sizeof(firmware_sign_algorithm));
+  kernel_ptr += FIELD_LEN(firmware_sign_algorithm);
+  Memcpy(&kernel_sign_algorithm, kernel_ptr, sizeof(kernel_sign_algorithm));
+  kernel_ptr += FIELD_LEN(kernel_sign_algorithm);
+  Memcpy(&kernel_key_version, kernel_ptr, sizeof(kernel_key_version));
+
+  if (firmware_sign_algorithm >= kNumAlgorithms)
+    return 0;
+  if (kernel_sign_algorithm >= kNumAlgorithms)
+    return 0;
+  kernel_key_signature_len = siglen_map[firmware_sign_algorithm];
+  kernel_sign_key_len = RSAProcessedKeySize(kernel_sign_algorithm);
+  kernel_ptr += (FIELD_LEN(kernel_key_version) +
+                 kernel_sign_key_len +
+                 FIELD_LEN(header_checksum) +
+                 kernel_key_signature_len);
+  Memcpy(&kernel_version, kernel_ptr, sizeof(kernel_version));
+  return CombineUint16Pair(kernel_key_version, kernel_version);
+}
+
+int VerifyKernelDriver_f(uint8_t* firmware_key_blob,
+                         kernel_entry* kernelA,
+                         kernel_entry* kernelB,
+                         int dev_mode) {
+  int i;
+  /* Contains the logical kernel version (32-bit) which is calculated as
+   * (kernel_key_version << 16 | kernel_version) where
+   * [kernel_key_version], [firmware_version] are both 16-bit.
+   */
+  uint32_t kernelA_lversion, kernelB_lversion;
+  uint32_t min_lversion;  /* Minimum of kernel A and kernel B lversion. */
+  uint32_t stored_lversion;  /* Stored logical version in the TPM. */
+  kernel_entry* try_kernel[2];  /* Kernel in try order. */
+  int try_kernel_which[2];  /* Which corresponding kernel in the try order */
+  uint32_t try_kernel_lversion[2];  /* Their logical versions. */
+
+  /* [kernel_to_boot] will eventually contain the boot path to follow
+   * and is returned to the caller. Initially, we set it to recovery. If
+   * a valid bootable kernel is found, it will be set to that. */
+  int kernel_to_boot = BOOT_KERNEL_RECOVERY_CONTINUE;
+
+
+  /* The TPM must already have be initialized, so no need to call SetupTPM(). */
+
+  /* We get the key versions by reading directly from the image blobs without
+   * any additional (expensive) sanity checking on the blob since it's faster to
+   * outright reject a kernel with an older kernel key version. A malformed
+   * or corrupted kernel blob will still fail when VerifyKernel() is called
+   * on it.
+   */
+  kernelA_lversion = GetLogicalKernelVersion(kernelA->kernel_blob);
+  kernelB_lversion = GetLogicalKernelVersion(kernelB->kernel_blob);
+  min_lversion  = Min(kernelA_lversion, kernelB_lversion);
+  stored_lversion = CombineUint16Pair(GetStoredVersion(KERNEL_KEY_VERSION),
+                                      GetStoredVersion(KERNEL_VERSION));
+
+  /* TODO(gauravsh): The kernel entries kernelA and kernelB come from the
+   * partition table - verify its signature/checksum before proceeding
+   * further. */
+
+  /* The logic for deciding which kernel to boot from is taken from the
+   * the Chromium OS Drive Map design document.
+   *
+   * We went to consider the kernels in their according to their boot
+   * priority attribute value.
+   */
+
+  if (kernelA->boot_priority >= kernelB->boot_priority) {
+    try_kernel[0] = kernelA;
+    try_kernel_which[0] = BOOT_KERNEL_A_CONTINUE;
+    try_kernel_lversion[0] = kernelA_lversion;
+    try_kernel[1] = kernelB;
+    try_kernel_which[1] = BOOT_KERNEL_B_CONTINUE;
+    try_kernel_lversion[1] = kernelB_lversion;
+  } else {
+    try_kernel[0] = kernelB;
+    try_kernel_which[0] = BOOT_KERNEL_B_CONTINUE;
+    try_kernel_lversion[0] = kernelB_lversion;
+    try_kernel[1] = kernelA;
+    try_kernel_which[1] = BOOT_KERNEL_A_CONTINUE;
+    try_kernel_lversion[1] = kernelA_lversion;
+  }
+
+  /* TODO(gauravsh): Changes to boot_tries_remaining and boot_priority
+   * below should be propagated to partition table. This will be added
+   * once the firmware parition table parsing code is in. */
+  for (i = 0; i < 2; i++) {
+    if ((try_kernel[i]->boot_success_flag ||
+         try_kernel[i]->boot_tries_remaining) &&
+        (VERIFY_KERNEL_SUCCESS == VerifyKernel(firmware_key_blob,
+                                               try_kernel[i]->kernel_blob,
+                                               dev_mode))) {
+      if (try_kernel[i]->boot_tries_remaining > 0)
+        try_kernel[i]->boot_tries_remaining--;
+      if (stored_lversion > try_kernel_lversion[i])
+        continue;  /* Rollback: I am afraid I can't let you do that Dave. */
+      if (i == 0 && (stored_lversion < try_kernel_lversion[1])) {
+        /* The higher priority kernel is valid and bootable, See if we
+         * need to update the stored version for rollback prevention. */
+        if (VERIFY_KERNEL_SUCCESS == VerifyKernel(firmware_key_blob,
+                                                  try_kernel[1]->kernel_blob,
+                                                  dev_mode)) {
+          WriteStoredVersion(KERNEL_KEY_VERSION,
+                             (uint16_t) (min_lversion >> 16));
+          WriteStoredVersion(KERNEL_VERSION,
+                             (uint16_t) (min_lversion & 0xFFFF));
+          stored_lversion = min_lversion;  /* Update stored version as it's
+                                            * used later. */
+        }
+      }
+      kernel_to_boot = try_kernel_which[i];
+      break;  /* We found a valid kernel. */
+    }
+    try_kernel[i]->boot_priority = 0;
+    }  /* for loop. */
+
+  /* Lock Kernel TPM rollback indices from further writes.
+   * TODO(gauravsh): Figure out if these can be combined into one
+   * 32-bit location since we seem to always use them together. This can help
+   * us minimize the number of NVRAM writes/locks (which are limited over flash
+   * memory lifetimes.
+   */
+  LockStoredVersion(KERNEL_KEY_VERSION);
+  LockStoredVersion(KERNEL_VERSION);
+  return kernel_to_boot;
+}