security EIA1: bugfix: memory alignment + read out of array

Compiling the nrUE with -fsanitize=undefined leads to a crash
because the function nas_stream_encrypt_eia1() accesses the data
as uint32_t but the data is not aligned.

Actually this function wants 64 bits (big-endian) of data, so let's
introduce a simple function to read a big-endian 64 bits value.
It may seem bad (unoptimized), but looking at the output of gcc
without -fsanitize=undefined this will be translated as just one
movbeq instruction (on the machine where I did the test), which is
actually less instructions than the previous version which was doing
too movbel plus orq.

Moreover, after the main loop we need to process the last remaining
bytes (so less than 8). The code was wrong, reading past the input
data (and also not caring about alignment). It may work, it may fail,
it depends on many things. But it's plain wrong. So this was replaced
for something better, simpler. No need for mask32bit() anymore, only
one call to U64() is needed.

And now -fsanitize=undefined is happy, so all is good.

We also restrict the input length to be multiple of 8 bits. I don't
think it's a problem. To be refined if I'm wrong. (I think RRC and
NAS messages are 8-bits aligned, so it shouldn't be a problem.)

openair3/SECU/nas_stream_eia1.c

@@ -88,25 +88,36 @@ static uint64_t MUL64(uint64_t V, uint64_t P, uint64_t c)
   return result;
 }
 
-/* mask32bit.
-* Input n: an integer in 1-32.
-* Output : a 32 bit mask.
-* Prepares a 32 bit mask with required number of 1 bits on the MSB side.
-*/
-static uint32_t mask32bit(int n)
+/* read a big endian uint64_t at given address (potentially not 64-bits aligned)
+ * don't read more than 'available_bytes'
+ * (use 0 if no byte to read)
+ * (note: the compiler will optimize this, no need to do better)
+ */
+static inline uint64_t U64(uint8_t *p, int available_bytes)
 {
-  uint32_t mask=0x0;
+  uint64_t a = 0;
+  uint64_t b = 0;
+  uint64_t c = 0;
+  uint64_t d = 0;
+  uint64_t e = 0;
+  uint64_t f = 0;
+  uint64_t g = 0;
+  uint64_t h = 0;
+  switch (available_bytes) {
+    case 8: h = p[7]; /* falltrough */
+    case 7: g = p[6]; /* falltrough */
+    case 6: f = p[5]; /* falltrough */
+    case 5: e = p[4]; /* falltrough */
+    case 4: d = p[3]; /* falltrough */
+    case 3: c = p[2]; /* falltrough */
+    case 2: b = p[1]; /* falltrough */
+    case 1: a = p[0];
+  }
 
-  if ( n%32 == 0 )
-    return 0xffffffff;
-
-  while (n--)
-    mask = (mask>>1) ^ 0x80000000;
-
-  return mask;
+  return (a << (32+24)) | (b << (32+16)) | (c << (32+8)) | (d << 32)
+         | (e << 24) | (f << 16) | (g << 8) | h;
 }
 
-
 /*!
  * @brief Create integrity cmac t for a given message.
  * @param[in] stream_cipher Structure containing various variables to setup encoding
@@ -125,11 +136,8 @@ void nas_stream_encrypt_eia1(nas_stream_cipher_t const *stream_cipher, uint8_t o
   uint64_t        c;
   uint64_t        M_D_2;
   int             rem_bits;
-  uint32_t        mask = 0;
-  uint32_t        *message;
   uint8_t         *key = (uint8_t *)stream_cipher->context;
 
-  message = (uint32_t*)stream_cipher->message; /* To operate 32 bit message internally. */
   /* Load the Integrity Key for SNOW3G initialization as in section 4.4. */
   memcpy(K+3,key+0,4); /*K[3] = key[0]; we assume
     K[3]=key[0]||key[1]||...||key[31] , with key[0] the
@@ -181,11 +189,14 @@ void nas_stream_encrypt_eia1(nas_stream_cipher_t const *stream_cipher, uint8_t o
   EVAL = 0;
   c = 0x1b;
 
+  AssertFatal(stream_cipher->blength % 8 == 0, "unsupported buffer length\n");
+
+  uint8_t *message = stream_cipher->message;
+
   /* for 0 <= i <= D-3 */
   for (i=0; i<D-2; i++) {
-    V = EVAL ^ ( (uint64_t)hton_int32(message[2*i]) << 32 | (uint64_t)hton_int32(message[2*i+1]) );
+    V = EVAL ^ U64(&message[4 * 2*i], 8);
     EVAL = MUL64(V,P,c);
-    //printf ("Mi: %16X %16X\tEVAL: %16lX\n",hton_int32(message[2*i]),hton_int32(message[2*i+1]), EVAL);
   }
 
   /* for D-2 */
@@ -194,14 +205,7 @@ void nas_stream_encrypt_eia1(nas_stream_cipher_t const *stream_cipher, uint8_t o
   if (rem_bits == 0)
     rem_bits = 64;
 
-  mask = mask32bit(rem_bits%32);
-
-  if (rem_bits > 32) {
-    M_D_2 = ( (uint64_t) hton_int32(message[2*(D-2)]) << 32 ) |
-            (uint64_t) (hton_int32(message[2*(D-2)+1]) &  mask);
-  } else {
-    M_D_2 = ( (uint64_t) hton_int32(message[2*(D-2)]) & mask) << 32 ;
-  }
+  M_D_2 = U64(&message[4 * (2*(D-2))], rem_bits/8);
 
   V = EVAL ^ M_D_2;
   EVAL = MUL64(V,P,c);