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aes: Add fault injection checks when writing key to hardware

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Vulnerability reported by LimitedResults under Espressif Bug Bounty Program.
This commit is contained in:
Angus Gratton 2019-05-21 18:12:42 +10:00 committed by Angus Gratton
parent 7c5dd19c83
commit 088439c634
2 changed files with 86 additions and 22 deletions
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102
components/esp32/hwcrypto/aes.c
View file

@ -50,6 +50,11 @@
*/
static portMUX_TYPE aes_spinlock = portMUX_INITIALIZER_UNLOCKED;
static inline bool valid_key_length(const esp_aes_context *ctx)
{
return ctx->key_bytes == 128/8 || ctx->key_bytes == 192/8 || ctx->key_bytes == 256/8;
}
void esp_aes_acquire_hardware( void )
{
portENTER_CRITICAL(&aes_spinlock);
@ -94,6 +99,7 @@ int esp_aes_setkey( esp_aes_context *ctx, const unsigned char *key,
}
ctx->key_bytes = keybits / 8;
memcpy(ctx->key, key, ctx->key_bytes);
ctx->key_in_hardware = 0;
return 0;
}
@ -103,28 +109,47 @@ int esp_aes_setkey( esp_aes_context *ctx, const unsigned char *key,
*
* Call only while holding esp_aes_acquire_hardware().
*/
static inline void esp_aes_setkey_hardware( esp_aes_context *ctx, int mode)
static void esp_aes_setkey_hardware(esp_aes_context *ctx, int mode)
{
const uint32_t MODE_DECRYPT_BIT = 4;
unsigned mode_reg_base = (mode == ESP_AES_ENCRYPT) ? 0 : MODE_DECRYPT_BIT;
ctx->key_in_hardware = 0;
for (int i = 0; i < ctx->key_bytes/4; ++i) {
DPORT_REG_WRITE(AES_KEY_BASE + i * 4, *(((uint32_t *)ctx->key) + i));
ctx->key_in_hardware += 4;
}
DPORT_REG_WRITE(AES_MODE_REG, mode_reg_base + ((ctx->key_bytes / 8) - 2));
/* Fault injection check: all words of key data should have been written to hardware */
if (ctx->key_in_hardware < 16
|| ctx->key_in_hardware != ctx->key_bytes) {
abort();
}
}
/* Run a single 16 byte block of AES, using the hardware engine.
*
* Call only while holding esp_aes_acquire_hardware().
*/
static void esp_aes_block(const void *input, void *output)
static int esp_aes_block(esp_aes_context *ctx, const void *input, void *output)
{
const uint32_t *input_words = (const uint32_t *)input;
uint32_t i0, i1, i2, i3;
uint32_t *output_words = (uint32_t *)output;
/* If no key is written to hardware yet, either the user hasn't called
mbedtls_aes_setkey_enc/mbedtls_aes_setkey_dec - meaning we also don't
know which mode to use - or a fault skipped the
key write to hardware. Treat this as a fatal error and zero the output block.
*/
if (ctx->key_in_hardware != ctx->key_bytes) {
bzero(output, 16);
return MBEDTLS_ERR_AES_INVALID_INPUT_LENGTH;
}
/* Storing i0,i1,i2,i3 in registers not an array
helps a lot with optimisations at -Os level */
i0 = input_words[0];
@ -153,11 +178,14 @@ static void esp_aes_block(const void *input, void *output)
Bypassing this check requires at least one additional fault.
*/
if(i0 == output_words[0] && i1 == output_words[1] && i2 == output_words[2] && i3 == output_words[3]) {
// calling two zeroing functions to narrow the
// window for a double-fault here
// calling zeroing functions to narrow the
// window for a double-fault of the abort step, here
memset(output, 0, 16);
mbedtls_platform_zeroize(output, 16);
abort();
}
return 0;
}
/*
@ -167,11 +195,18 @@ int esp_internal_aes_encrypt( esp_aes_context *ctx,
const unsigned char input[16],
unsigned char output[16] )
{
int r;
if (!valid_key_length(ctx)) {
return MBEDTLS_ERR_AES_INVALID_KEY_LENGTH;
}
esp_aes_acquire_hardware();
ctx->key_in_hardware = 0;
esp_aes_setkey_hardware(ctx, ESP_AES_ENCRYPT);
esp_aes_block(input, output);
r = esp_aes_block(ctx, input, output);
esp_aes_release_hardware();
return 0;
return r;
}
void esp_aes_encrypt( esp_aes_context *ctx,
@ -189,11 +224,18 @@ int esp_internal_aes_decrypt( esp_aes_context *ctx,
const unsigned char input[16],
unsigned char output[16] )
{
int r;
if (!valid_key_length(ctx)) {
return MBEDTLS_ERR_AES_INVALID_KEY_LENGTH;
}
esp_aes_acquire_hardware();
ctx->key_in_hardware = 0;
esp_aes_setkey_hardware(ctx, ESP_AES_DECRYPT);
esp_aes_block(input, output);
r = esp_aes_block(ctx, input, output);
esp_aes_release_hardware();
return 0;
return r;
}
void esp_aes_decrypt( esp_aes_context *ctx,
@ -203,7 +245,6 @@ void esp_aes_decrypt( esp_aes_context *ctx,
esp_internal_aes_decrypt(ctx, input, output);
}
/*
* AES-ECB block encryption/decryption
*/
@ -212,12 +253,19 @@ int esp_aes_crypt_ecb( esp_aes_context *ctx,
const unsigned char input[16],
unsigned char output[16] )
{
int r;
if (!valid_key_length(ctx)) {
return MBEDTLS_ERR_AES_INVALID_KEY_LENGTH;
}
esp_aes_acquire_hardware();
ctx->key_in_hardware = 0;
esp_aes_setkey_hardware(ctx, mode);
esp_aes_block(input, output);
r = esp_aes_block(ctx, input, output);
esp_aes_release_hardware();
return 0;
return r;
}
@ -241,14 +289,19 @@ int esp_aes_crypt_cbc( esp_aes_context *ctx,
return ( ERR_ESP_AES_INVALID_INPUT_LENGTH );
}
if (!valid_key_length(ctx)) {
return MBEDTLS_ERR_AES_INVALID_KEY_LENGTH;
}
esp_aes_acquire_hardware();
ctx->key_in_hardware = 0;
esp_aes_setkey_hardware(ctx, mode);
if ( mode == ESP_AES_DECRYPT ) {
while ( length > 0 ) {
memcpy(temp, input_words, 16);
esp_aes_block(input_words, output_words);
esp_aes_block(ctx, input_words, output_words);
for ( i = 0; i < 4; i++ ) {
output_words[i] = output_words[i] ^ iv_words[i];
@ -267,7 +320,7 @@ int esp_aes_crypt_cbc( esp_aes_context *ctx,
output_words[i] = input_words[i] ^ iv_words[i];
}
esp_aes_block(output_words, output_words);
esp_aes_block(ctx, output_words, output_words);
memcpy( iv_words, output_words, 16 );
input_words += 4;
@ -295,14 +348,19 @@ int esp_aes_crypt_cfb128( esp_aes_context *ctx,
int c;
size_t n = *iv_off;
if (!valid_key_length(ctx)) {
return MBEDTLS_ERR_AES_INVALID_KEY_LENGTH;
}
esp_aes_acquire_hardware();
ctx->key_in_hardware = 0;
esp_aes_setkey_hardware(ctx, ESP_AES_ENCRYPT);
if ( mode == ESP_AES_DECRYPT ) {
while ( length-- ) {
if ( n == 0 ) {
esp_aes_block(iv, iv );
esp_aes_block(ctx, iv, iv );
}
c = *input++;
@ -314,7 +372,7 @@ int esp_aes_crypt_cfb128( esp_aes_context *ctx,
} else {
while ( length-- ) {
if ( n == 0 ) {
esp_aes_block(iv, iv );
esp_aes_block(ctx, iv, iv );
}
iv[n] = *output++ = (unsigned char)( iv[n] ^ *input++ );
@ -343,13 +401,18 @@ int esp_aes_crypt_cfb8( esp_aes_context *ctx,
unsigned char c;
unsigned char ov[17];
if (!valid_key_length(ctx)) {
return MBEDTLS_ERR_AES_INVALID_KEY_LENGTH;
}
esp_aes_acquire_hardware();
ctx->key_in_hardware = 0;
esp_aes_setkey_hardware(ctx, ESP_AES_ENCRYPT);
while ( length-- ) {
memcpy( ov, iv, 16 );
esp_aes_block(iv, iv);
esp_aes_block(ctx, iv, iv);
if ( mode == ESP_AES_DECRYPT ) {
ov[16] = *input;
@ -383,13 +446,18 @@ int esp_aes_crypt_ctr( esp_aes_context *ctx,
int c, i;
size_t n = *nc_off;
if (!valid_key_length(ctx)) {
return MBEDTLS_ERR_AES_INVALID_KEY_LENGTH;
}
esp_aes_acquire_hardware();
ctx->key_in_hardware = 0;
esp_aes_setkey_hardware(ctx, ESP_AES_ENCRYPT);
while ( length-- ) {
if ( n == 0 ) {
esp_aes_block(nonce_counter, stream_block);
esp_aes_block(ctx, nonce_counter, stream_block);
for ( i = 16; i > 0; i-- )
if ( ++nonce_counter[i - 1] != 0 ) {

6
components/esp32/include/hwcrypto/aes.h
View file

@ -41,17 +41,13 @@ extern "C" {
/**
* \brief AES context structure
*
* \note buf is able to hold 32 extra bytes, which can be used:
* - for alignment purposes if VIA padlock is used, and/or
* - to simplify key expansion in the 256-bit case by
* generating an extra round key
*/
typedef struct {
uint8_t key_bytes;
volatile uint8_t key_in_hardware; /* This variable is used for fault injection checks, so marked volatile to avoid optimisation */
uint8_t key[32];
} esp_aes_context;
/**
* \brief The AES XTS context-type definition.
*/