Refactor AES context to be shallow-copyable

Replace RK pointer in AES context with a buffer offset, to allow
shallow copying. Fixes #2147.

Signed-off-by: Werner Lewis <werner.lewis@arm.com>

ChangeLog.d/fix-aes-shallow-copying.txt

@@ -0,0 +1,2 @@
+Bugfix
+   * Refactor mbedtls_aes_context to support shallow-copying. Fixes #2147.

include/mbedtls/aes.h

@@ -80,7 +80,7 @@ extern "C" {
 typedef struct mbedtls_aes_context
 {
     int MBEDTLS_PRIVATE(nr);                     /*!< The number of rounds. */
-    uint32_t *MBEDTLS_PRIVATE(rk);               /*!< AES round keys. */
+    size_t MBEDTLS_PRIVATE(rk_offset);           /*!< Buffer offset for AES round keys. */
     uint32_t MBEDTLS_PRIVATE(buf)[68];           /*!< Unaligned data buffer. This buffer can
                                      hold 32 extra Bytes, which can be used for
                                      one of the following purposes:

library/aes.c

@@ -555,14 +555,15 @@ int mbedtls_aes_setkey_enc( mbedtls_aes_context *ctx, const unsigned char *key,
         aes_padlock_ace = mbedtls_padlock_has_support( MBEDTLS_PADLOCK_ACE );
 
     if( aes_padlock_ace )
-        ctx->rk = RK = MBEDTLS_PADLOCK_ALIGN16( ctx->buf );
+        ctx->rk_offset = MBEDTLS_PADLOCK_ALIGN16( ctx->buf ) - ctx->buf;
     else
 #endif
-    ctx->rk = RK = ctx->buf;
+    ctx->rk_offset = 0;
+    RK = ctx->buf + ctx->rk_offset;
 
 #if defined(MBEDTLS_AESNI_C) && defined(MBEDTLS_HAVE_X86_64)
     if( mbedtls_aesni_has_support( MBEDTLS_AESNI_AES ) )
-        return( mbedtls_aesni_setkey_enc( (unsigned char *) ctx->rk, key, keybits ) );
+        return( mbedtls_aesni_setkey_enc( (unsigned char *) RK, key, keybits ) );
 #endif
 
     for( i = 0; i < ( keybits >> 5 ); i++ )
@@ -659,10 +660,11 @@ int mbedtls_aes_setkey_dec( mbedtls_aes_context *ctx, const unsigned char *key,
         aes_padlock_ace = mbedtls_padlock_has_support( MBEDTLS_PADLOCK_ACE );
 
     if( aes_padlock_ace )
-        ctx->rk = RK = MBEDTLS_PADLOCK_ALIGN16( ctx->buf );
+        ctx->rk_offset = MBEDTLS_PADLOCK_ALIGN16( ctx->buf ) - ctx->buf;
     else
 #endif
-    ctx->rk = RK = ctx->buf;
+    ctx->rk_offset = 0;
+    RK = ctx->buf + ctx->rk_offset;
 
     /* Also checks keybits */
     if( ( ret = mbedtls_aes_setkey_enc( &cty, key, keybits ) ) != 0 )
@@ -673,13 +675,13 @@ int mbedtls_aes_setkey_dec( mbedtls_aes_context *ctx, const unsigned char *key,
 #if defined(MBEDTLS_AESNI_C) && defined(MBEDTLS_HAVE_X86_64)
     if( mbedtls_aesni_has_support( MBEDTLS_AESNI_AES ) )
     {
-        mbedtls_aesni_inverse_key( (unsigned char *) ctx->rk,
+        mbedtls_aesni_inverse_key( (unsigned char *) RK,
-                           (const unsigned char *) cty.rk, ctx->nr );
+                           (const unsigned char *) ( cty.buf + cty.rk_offset ), ctx->nr );
         goto exit;
     }
 #endif
 
-    SK = cty.rk + cty.nr * 4;
+    SK = cty.buf + cty.rk_offset + cty.nr * 4;
 
     *RK++ = *SK++;
     *RK++ = *SK++;
@@ -843,7 +845,7 @@ int mbedtls_internal_aes_encrypt( mbedtls_aes_context *ctx,
                                   unsigned char output[16] )
 {
     int i;
-    uint32_t *RK = ctx->rk;
+    uint32_t *RK = ctx->buf + ctx->rk_offset;
     struct
     {
         uint32_t X[4];
@@ -907,7 +909,7 @@ int mbedtls_internal_aes_decrypt( mbedtls_aes_context *ctx,
                                   unsigned char output[16] )
 {
     int i;
-    uint32_t *RK = ctx->rk;
+    uint32_t *RK = ctx->buf + ctx->rk_offset;
     struct
     {
         uint32_t X[4];
@@ -971,7 +973,6 @@ int mbedtls_aes_crypt_ecb( mbedtls_aes_context *ctx,
                            unsigned char output[16] )
 {
     AES_VALIDATE_RET( ctx != NULL );
-    AES_VALIDATE_RET( ctx->rk != NULL );
     AES_VALIDATE_RET( input != NULL );
     AES_VALIDATE_RET( output != NULL );
     AES_VALIDATE_RET( mode == MBEDTLS_AES_ENCRYPT ||

library/aesni.c

@@ -127,7 +127,7 @@ int mbedtls_aesni_crypt_ecb( mbedtls_aes_context *ctx,
          "3:                        \n\t"
          "movdqu    %%xmm0, (%4)    \n\t" // export output
          :
-         : "r" (ctx->nr), "r" (ctx->rk), "r" (mode), "r" (input), "r" (output)
+         : "r" (ctx->nr), "r" (ctx->buf + ctx->rk_offset), "r" (mode), "r" (input), "r" (output)
          : "memory", "cc", "xmm0", "xmm1" );
 
 

library/padlock.c

@@ -82,7 +82,7 @@ int mbedtls_padlock_xcryptecb( mbedtls_aes_context *ctx,
     uint32_t *ctrl;
     unsigned char buf[256];
 
-    rk  = ctx->rk;
+    rk  = ctx->buf + ctx->rk_offset;
     blk = MBEDTLS_PADLOCK_ALIGN16( buf );
     memcpy( blk, input, 16 );
 
@@ -129,7 +129,7 @@ int mbedtls_padlock_xcryptcbc( mbedtls_aes_context *ctx,
         ( (long) output & 15 ) != 0 )
         return( MBEDTLS_ERR_PADLOCK_DATA_MISALIGNED );
 
-    rk = ctx->rk;
+    rk = ctx->buf + ctx->rk_offset;
     iw = MBEDTLS_PADLOCK_ALIGN16( buf );
     memcpy( iw, iv, 16 );
 

tests/suites/test_suite_aes.ecb.data

@@ -228,3 +228,6 @@ aes_decrypt_ecb:"000000000000000000000000000000000000000000000000000000000000000
 
 AES-256-ECB Decrypt NIST KAT #12
 aes_decrypt_ecb:"0000000000000000000000000000000000000000000000000000000000000000":"9b80eefb7ebe2d2b16247aa0efc72f5d":"e0000000000000000000000000000000":0
+
+AES-256-ECB Copy Context NIST KAT #1
+aes_ecb_copy_context:"c1cc358b449909a19436cfbb3f852ef8bcb5ed12ac7058325f56e6099aab1a1c":"00000000000000000000000000000000"

tests/suites/test_suite_aes.function

@@ -460,6 +460,35 @@ void aes_misc_params( )
 }
 /* END_CASE */
 
+/* BEGIN_CASE */
+void aes_ecb_copy_context( data_t * key_str, data_t * src_str )
+{
+    unsigned char output1[16], output2[16], plain[16];
+    mbedtls_aes_context ctx1, ctx2;
+
+    // Set key and encrypt with original context
+    mbedtls_aes_init( &ctx1 );
+    TEST_ASSERT( mbedtls_aes_setkey_enc( &ctx1, key_str->x,
+                                         key_str->len * 8 ) == 0 );
+    TEST_ASSERT( mbedtls_aes_crypt_ecb( &ctx1, MBEDTLS_AES_ENCRYPT,
+                                        src_str->x, output1 ) == 0 );
+
+    ctx2 = ctx1;
+    memset( &ctx1, 0, sizeof( ctx1 ) );
+
+    // Encrypt with copied context and decrypt
+    TEST_ASSERT( mbedtls_aes_crypt_ecb( &ctx2, MBEDTLS_AES_ENCRYPT,
+                                        src_str->x, output2 ) == 0 );
+    TEST_ASSERT( mbedtls_aes_setkey_dec( &ctx2, key_str->x,
+                                         key_str->len * 8) == 0 );
+    TEST_ASSERT( mbedtls_aes_crypt_ecb( &ctx2, MBEDTLS_AES_DECRYPT,
+                                        output1, plain ) == 0 );
+
+    TEST_ASSERT( mbedtls_test_hexcmp( output1, output2, 16, 16 ) == 0 );
+    TEST_ASSERT( mbedtls_test_hexcmp( src_str->x, plain, src_str->len, 16) == 0 );
+}
+/* END_CASE */
+
 /* BEGIN_CASE depends_on:MBEDTLS_SELF_TEST */
 void aes_selftest(  )
 {