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László Monda
2016-08-10 01:45:15 +02:00
commit e6c1fce5b4
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apps/elftosb/common/EncoreBootImageReader.cpp Normal file
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/*
* File: EncoreBootImageReader.cpp
*
* Copyright (c) Freescale Semiconductor, Inc. All rights reserved.
* See included license file for license details.
*/
#include "EncoreBootImageReader.h"
#include "SHA1.h"
#include "rijndael.h"
#include "RijndaelCBCMAC.h"
#include <assert.h>
#include "EndianUtilities.h"
#include "Logging.h"
using namespace elftosb;
//! \post Stream head points to just after the image header.
//! \exception read_error Thrown if the image header is invalid.
void EncoreBootImageReader::readImageHeader()
{
// seek to beginning of the stream/file and read the plaintext header
m_stream.seekg(0, std::ios_base::beg);
if (m_stream.read((char *)&m_header, sizeof(m_header)).bad())
{
throw read_error("failed to read image header");
}
m_header.m_flags = ENDIAN_LITTLE_TO_HOST_U16(m_header.m_flags);
m_header.m_imageBlocks = ENDIAN_LITTLE_TO_HOST_U32(m_header.m_imageBlocks);
m_header.m_firstBootTagBlock = ENDIAN_LITTLE_TO_HOST_U32(m_header.m_firstBootTagBlock);
m_header.m_firstBootableSectionID = ENDIAN_LITTLE_TO_HOST_U32(m_header.m_firstBootableSectionID);
m_header.m_keyCount = ENDIAN_LITTLE_TO_HOST_U16(m_header.m_keyCount);
m_header.m_keyDictionaryBlock = ENDIAN_LITTLE_TO_HOST_U16(m_header.m_keyDictionaryBlock);
m_header.m_headerBlocks = ENDIAN_LITTLE_TO_HOST_U16(m_header.m_headerBlocks);
m_header.m_sectionCount = ENDIAN_LITTLE_TO_HOST_U16(m_header.m_sectionCount);
m_header.m_sectionHeaderSize = ENDIAN_LITTLE_TO_HOST_U16(m_header.m_sectionHeaderSize);
m_header.m_timestamp = ENDIAN_LITTLE_TO_HOST_U64(m_header.m_timestamp);
// m_header.m_componentVersion.m_major = ENDIAN_BIG_TO_HOST_U16(m_header.m_componentVersion.m_major);
// m_header.m_componentVersion.m_minor = ENDIAN_BIG_TO_HOST_U16(m_header.m_componentVersion.m_minor);
// m_header.m_componentVersion.m_revision = ENDIAN_BIG_TO_HOST_U16(m_header.m_componentVersion.m_revision);
// m_header.m_productVersion.m_major = ENDIAN_BIG_TO_HOST_U16(m_header.m_productVersion.m_major);
// m_header.m_productVersion.m_minor = ENDIAN_BIG_TO_HOST_U16(m_header.m_productVersion.m_minor);
// m_header.m_productVersion.m_revision = ENDIAN_BIG_TO_HOST_U16(m_header.m_productVersion.m_revision);
// check header signature 1
if (m_header.m_signature[0] != 'S' || m_header.m_signature[1] != 'T' || m_header.m_signature[2] != 'M' ||
m_header.m_signature[3] != 'P')
{
throw read_error("invalid signature 1");
}
// check header signature 2 for version 1.1 and greater
if ((m_header.m_majorVersion > 1 || (m_header.m_majorVersion == 1 && m_header.m_minorVersion >= 2)) &&
(m_header.m_signature2[0] != 's' || m_header.m_signature2[1] != 'g' || m_header.m_signature2[2] != 't' ||
m_header.m_signature2[3] != 'l'))
{
// throw read_error("invalid signature 2");
Log::log(Logger::WARNING, "warning: invalid signature 2\n");
}
}
//! \pre The image header must have already been read with a call to readImageHeader().
//!
void EncoreBootImageReader::computeHeaderDigest(sha1_digest_t &digest)
{
CSHA1 hash;
hash.Reset();
hash.Update((uint8_t *)&m_header.m_signature, sizeof(m_header) - sizeof(sha1_digest_t));
hash.Final();
hash.GetHash(digest);
}
//! \pre The image header must have already been read.
//! \pre The DEK must have been found already.
//! \post The stream head is at the end of the digest.
void EncoreBootImageReader::readImageDigest()
{
unsigned digestPosition = sizeOfCipherBlocks(m_header.m_imageBlocks - 2);
m_stream.seekg(digestPosition, std::ios_base::beg);
// read the two cipher blocks containing the digest, including padding
cipher_block_t digestBlocks[2];
if (m_stream.read((char *)&digestBlocks, sizeof(digestBlocks)).bad())
{
throw read_error("failed to read image digest");
}
// decrypt the digest
if (isEncrypted())
{
Rijndael cipher;
cipher.init(Rijndael::CBC, Rijndael::Decrypt, m_dek, Rijndael::Key16Bytes, m_header.m_iv);
cipher.blockDecrypt((uint8_t *)&digestBlocks, sizeof(digestBlocks) * 8, (uint8_t *)&digestBlocks);
}
// copy the digest out of the padded blocks
memcpy(m_digest, &digestBlocks, sizeof(m_digest));
}
//! \pre The image header must have already been read with a call to readImageHeader().
//! \post The stream head is at the end of the image minus the last two cipher blocks.
//! \param digest Where to store the resulting digest.
//! \exception read_error Thrown if the image header is invalid.
void EncoreBootImageReader::computeImageDigest(sha1_digest_t &digest)
{
m_stream.seekg(0, std::ios_base::beg);
CSHA1 hash;
hash.Reset();
unsigned blockCount = m_header.m_imageBlocks - 2; // exclude digest at end of image
while (blockCount--)
{
cipher_block_t block;
if (m_stream.read((char *)&block, sizeof(block)).bad())
{
throw read_error("failed to read block while computing image digest");
}
hash.Update(block, sizeof(block));
}
hash.Final();
hash.GetHash(digest);
}
//! \pre Image header must have been read before this method is called.
//!
void EncoreBootImageReader::readSectionTable()
{
// seek to the table
m_stream.seekg(sizeOfCipherBlocks(m_header.m_headerBlocks), std::ios_base::beg);
unsigned sectionCount = m_header.m_sectionCount;
while (sectionCount--)
{
EncoreBootImage::section_header_t header;
if (m_stream.read((char *)&header, sizeof(header)).bad())
{
throw read_error("failed to read section header");
}
// swizzle section header
header.m_tag = ENDIAN_LITTLE_TO_HOST_U32(header.m_tag);
header.m_offset = ENDIAN_LITTLE_TO_HOST_U32(header.m_offset);
header.m_length = ENDIAN_LITTLE_TO_HOST_U32(header.m_length);
header.m_flags = ENDIAN_LITTLE_TO_HOST_U32(header.m_flags);
m_sections.push_back(header);
}
}
//! Requires that an OTP key has been provided as the sole argument. Passing the
//! key into this method lets the caller search the key dictionary for any number
//! of keys and determine which are valid. If \a kek is found in the dictionary,
//! the decrypted DEK is saved and true is returned. A result of false means
//! that \a kek was not found.
//!
//! \pre The image header and section table must have been read already.
//! \post The stream head points somewhere inside the key dictionary, or just after it.
//! \post If the search was successful, the #m_dek member will contain the decrypted
//! session key. Otherwise #m_dek is not modified.
//! \param kek Search for this KEK in the dictionary.
//! \retval true The DEK was found and decrypted. True is also returned when the
//! image is not encrypted at all.
//! \retval false No matching key entry was found. The image cannot be decrypted.
bool EncoreBootImageReader::readKeyDictionary(const AESKey<128> &kek)
{
// do nothing if the image is not encrypted
if (!isEncrypted())
{
return true;
}
// first compute a CBC-MAC over the image header with our KEK
RijndaelCBCMAC mac(kek);
mac.update((const uint8_t *)&m_header, sizeof(m_header));
// run the CBC-MAC over each entry in the section table too
section_array_t::iterator it = m_sections.begin();
for (; it != m_sections.end(); ++it)
{
mac.update((const uint8_t *)&(*it), sizeof(EncoreBootImage::section_header_t));
}
// get the CBC-MAC result
mac.finalize();
const RijndaelCBCMAC::block_t &macResult = mac.getMAC();
// seek to the key dictionary
m_stream.seekg(sizeOfCipherBlocks(m_header.m_keyDictionaryBlock), std::ios_base::beg);
// decipher each key entry
unsigned entries = m_header.m_keyCount;
while (entries--)
{
// read the entry
EncoreBootImage::dek_dictionary_entry_t entry;
if (m_stream.read((char *)&entry, sizeof(entry)).bad())
{
throw read_error("failed to read key dictionary entry");
}
// compare the CBC-MAC we computed with the one in this entry
if (memcmp(macResult, entry.m_mac, sizeof(cipher_block_t)) == 0)
{
// it's a match! now decrypt this entry's key in place
Rijndael cipher;
cipher.init(Rijndael::CBC, Rijndael::Decrypt, kek, Rijndael::Key16Bytes, m_header.m_iv);
cipher.blockDecrypt(entry.m_dek, sizeof(entry.m_dek) * 8, entry.m_dek);
m_dek = entry.m_dek;
memset(entry.m_dek, 0, sizeof(entry.m_dek)); // wipe the key value from memory
return true;
}
}
// if we exit the loop normally then no matching MAC was found
return false;
}
//! Before the boot tag is added to the #m_bootTags member, some basic checks are performed.
//! The command tag field is checked to make sure it matches #ROM_TAG_CMD. And
//! the checksum field is verified to be sure it's correct.
//!
//! After the call to this method returns, the array of boot tags is accessible
//! with the getBootTags() method. The array is sorted in the order in which
//! the boot tags appeared in the image.
//!
//! \pre Image header must have been read.
//! \pre Key dictionary must have been read and a valid DEK found.
//! \post The stream head is left pointing just after the last boot tag.
//! \exception read_error A failure to read the boot tag, or a failure on one
//! of the consistency checks will cause this exception to be thrown.
void EncoreBootImageReader::readBootTags()
{
assert(m_header.m_firstBootTagBlock != 0);
unsigned bootTagOffset = m_header.m_firstBootTagBlock;
while (1)
{
// seek to this boot tag and read it into a temporary buffer
EncoreBootImage::boot_command_t header;
m_stream.seekg(sizeOfCipherBlocks(bootTagOffset), std::ios_base::beg);
if (m_stream.read((char *)&header, sizeof(header)).bad())
{
throw read_error("failed to read boot tag");
}
// swizzle to command header
header.m_flags = ENDIAN_LITTLE_TO_HOST_U16(header.m_flags);
header.m_address = ENDIAN_LITTLE_TO_HOST_U32(header.m_address);
header.m_count = ENDIAN_LITTLE_TO_HOST_U32(header.m_count);
header.m_data = ENDIAN_LITTLE_TO_HOST_U32(header.m_data);
// decrypt in place
if (isEncrypted())
{
Rijndael cipher;
cipher.init(Rijndael::CBC, Rijndael::Decrypt, m_dek, Rijndael::Key16Bytes, m_header.m_iv);
cipher.blockDecrypt((uint8_t *)&header, sizeof(header) * 8, (uint8_t *)&header);
}
// perform some basic checks
if (header.m_tag != EncoreBootImage::ROM_TAG_CMD)
{
throw read_error("boot tag is wrong command type");
}
uint8_t checksum = calculateCommandChecksum(header);
if (checksum != header.m_checksum)
{
throw read_error("boot tag checksum is invalid");
}
// save this boot tag
m_bootTags.push_back(header);
// and finally, update offset and break out of loop
bootTagOffset += header.m_count + 1; // include this boot tag in offset
if (header.m_flags & EncoreBootImage::ROM_LAST_TAG || bootTagOffset >= m_header.m_imageBlocks - 2)
{
break;
}
}
}
uint8_t EncoreBootImageReader::calculateCommandChecksum(EncoreBootImage::boot_command_t &header)
{
uint8_t *bytes = reinterpret_cast<uint8_t *>(&header);
uint8_t checksum = 0x5a;
int i;
// start at one to skip checksum field
for (i = 1; i < sizeof(header); ++i)
{
checksum += bytes[i];
}
return checksum;
}
//! \param index The index of the section to read.
//!
//! \pre Both the image header and section table must have been read already before
//! calling this method.
//! \exception read_error This exception is raised if the stream reports an error while
//! trying to read from the section.
EncoreBootImage::Section *EncoreBootImageReader::readSection(unsigned index)
{
// look up section header
assert(index < m_sections.size());
EncoreBootImage::section_header_t &header = m_sections[index];
// seek to the section
m_stream.seekg(sizeOfCipherBlocks(header.m_offset), std::ios_base::beg);
uint8_t *contents = NULL;
try
{
// allocate memory for the section contents and read the whole thing
unsigned contentLength = sizeOfCipherBlocks(header.m_length);
contents = new uint8_t[contentLength];
if (m_stream.read((char *)contents, contentLength).bad())
{
throw read_error("failed to read section");
}
// decrypt the entire section at once, if the image is encrypted and
// the cleartext flag is not set
if (isEncrypted() && (header.m_flags & EncoreBootImage::ROM_SECTION_CLEARTEXT) == 0)
{
Rijndael cipher;
cipher.init(Rijndael::CBC, Rijndael::Decrypt, m_dek, Rijndael::Key16Bytes, m_header.m_iv);
cipher.blockDecrypt(contents, contentLength * 8, contents);
}
// create section object
EncoreBootImage::Section *resultSection = NULL;
if (header.m_flags & EncoreBootImage::ROM_SECTION_BOOTABLE)
{
// a boot command section.
EncoreBootImage::BootSection *bootSection = new EncoreBootImage::BootSection(header.m_tag);
bootSection->fillFromData((cipher_block_t *)contents, header.m_length);
resultSection = bootSection;
}
else
{
// this is a raw data section
EncoreBootImage::DataSection *dataSection = new EncoreBootImage::DataSection(header.m_tag);
dataSection->setDataNoCopy(contents, contentLength);
contents = NULL;
resultSection = dataSection;
}
return resultSection;
}
catch (...)
{
if (contents)
{
delete[] contents;
}
throw;
}
}