crypto: arm64/aes-ccm - fix logical bug in AAD MAC handling

The NEON MAC calculation routine fails to handle the case correctly
where there is some data in the buffer, and the input fills it up
exactly. In this case, we enter the loop at the end with w8 == 0,
while a negative value is assumed, and so the loop carries on until
the increment of the 32-bit counter wraps around, which is quite
obviously wrong.

So omit the loop altogether in this case, and exit right away.
Reported-by: NEric Biggers <ebiggers@kernel.org>
Fixes: a3fd8210 ("arm64/crypto: AES in CCM mode using ARMv8 Crypto ...")
Cc: stable@vger.kernel.org
Signed-off-by: NArd Biesheuvel <ard.biesheuvel@linaro.org>
Signed-off-by: NHerbert Xu <herbert@gondor.apana.org.au>

arch/arm64/crypto/aes-ce-ccm-core.S

@@ -74,12 +74,13 @@ ENTRY(ce_aes_ccm_auth_data)
 	beq	10f
 	ext	v0.16b, v0.16b, v0.16b, #1	/* rotate out the mac bytes */
 	b	7b
-8:	mov	w7, w8
+8:	cbz	w8, 91f
+	mov	w7, w8
 	add	w8, w8, #16
 9:	ext	v1.16b, v1.16b, v1.16b, #1
 	adds	w7, w7, #1
 	bne	9b
-	eor	v0.16b, v0.16b, v1.16b
+91:	eor	v0.16b, v0.16b, v1.16b
 	st1	{v0.16b}, [x0]
 10:	str	w8, [x3]
 	ret