utility: add a simple tool for dumping the kernel config

utility/dump_kernel_config.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.
+ *
+ * Exports the kernel commandline from a given partition/image.
+ */
+
+#include <inttypes.h>  /* For uint64_t */
+#include <stdio.h>
+#include <stdlib.h>
+#include <sys/mman.h>
+#include <unistd.h>
+
+#include "kernel_blob.h"
+#include "utility.h"
+#include "vboot_common.h"
+#include "vboot_struct.h"
+
+/* Print help and return error */
+static int PrintHelp(void) {
+  puts("dump_kernel_config - Prints the kernel command line\n"
+       "\n"
+       "Usage:  dump_kernel_config <image/blockdevice>\n"
+       "\n"
+       "");
+  return 1;
+}
+
+static uint8_t* find_kernel_config(uint8_t* blob, uint64_t blob_size) {
+  VbKeyBlockHeader* key_block;
+  VbKernelPreambleHeader* preamble;
+  struct linux_kernel_params *params;
+  uint32_t now = 0;
+  uint32_t offset = 0;
+
+  /* Skip the key block */
+  key_block = (VbKeyBlockHeader*)blob;
+  now += key_block->key_block_size;
+  if (now + blob > blob + blob_size) {
+    error("key_block_size advances past the end of the blob\n");
+    return NULL;
+  }
+
+  /* Open up the preamble */
+  preamble = (VbKernelPreambleHeader*)(blob + now);
+  now += preamble->preamble_size;
+  if (now + blob > blob + blob_size) {
+    error("preamble_size advances past the end of the blob\n");
+    return NULL;
+  }
+
+  /* The parameters are packed before the bootloader and there is no specific
+   * pointer to it so we just walk back by its allocated size. */
+  offset = preamble->bootloader_address -
+           (CROS_32BIT_ENTRY_ADDR + CROS_PARAMS_SIZE) + now;
+  if (offset > blob_size) {
+    error("params are outside of the memory blob: %x\n", offset);
+    return NULL;
+  }
+  params = (struct linux_kernel_params *)(blob + offset);
+
+  /* Grab the offset to the kernel command line using the supplied pointer. */
+  offset = params->cmd_line_ptr - CROS_32BIT_ENTRY_ADDR + now;
+  if (offset > blob_size) {
+    error("cmdline is outside of the memory blob: %x\n", offset);
+    return NULL;
+  }
+  return (uint8_t *)(blob + offset);
+}
+
+static void* MapFile(const char *filename, size_t *size) {
+  FILE* f;
+  uint8_t* buf;
+  long file_size = 0;
+
+  f = fopen(filename, "rb");
+  if (!f) {
+    debug("Unable to open file %s\n", filename);
+    return NULL;
+  }
+
+  fseek(f, 0, SEEK_END);
+  file_size = ftell(f);
+  rewind(f);
+
+  if (file_size <= 0) {
+    fclose(f);
+    return NULL;
+  }
+  *size = (size_t) file_size;
+
+  /* Uses a host primitive as this is not meant for firmware use. */
+  buf = mmap(NULL, *size, PROT_READ, MAP_PRIVATE, fileno(f), 0);
+  if (buf == MAP_FAILED) {
+    error("Failed to mmap the file %s\n", filename);
+    fclose(f);
+    return NULL;
+  }
+
+  fclose(f);
+  return buf;
+}
+
+int main(int argc, char* argv[]) {
+  uint8_t* blob;
+  size_t blob_size;
+  char* infile = argv[1];
+  uint8_t *config = NULL;
+
+  if (argc < 2)
+    return PrintHelp();
+
+  if (!infile || !*infile) {
+    error("Must specify filename\n");
+    return 1;
+  }
+
+  /* Map the kernel image blob. */
+  blob = MapFile(infile, &blob_size);
+  if (!blob) {
+    error("Error reading input file\n");
+    return 1;
+  }
+
+  config = find_kernel_config(blob, (uint64_t)blob_size);
+  if (!config) {
+    error("Error parsing input file\n");
+    munmap(blob, blob_size);
+    return 1;
+  }
+
+  printf("%.*s", CROS_CONFIG_SIZE, config);
+  munmap(blob, blob_size);
+  return 0;
+}