crypto: arm64/aes-neonbs - fix returning final keystream block

commit 12455e32 upstream.

The arm64 NEON bit-sliced implementation of AES-CTR fails the improved
skcipher tests because it sometimes produces the wrong ciphertext.  The
bug is that the final keystream block isn't returned from the assembly
code when the number of non-final blocks is zero.  This can happen if
the input data ends a few bytes after a page boundary.  In this case the
last bytes get "encrypted" by XOR'ing them with uninitialized memory.

Fix the assembly code to return the final keystream block when needed.

Fixes: 88a3f582 ("crypto: arm64/aes - don't use IV buffer to return final keystream block")
Cc: <stable@vger.kernel.org> # v4.11+
Reviewed-by: Ard Biesheuvel <ard.biesheuvel@linaro.org>
Signed-off-by: Eric Biggers <ebiggers@google.com>
Signed-off-by: Herbert Xu <herbert@gondor.apana.org.au>
Signed-off-by: Greg Kroah-Hartman <gregkh@linuxfoundation.org>

arch/arm64/crypto/aes-neonbs-core.S

@@ -940,7 +940,7 @@ CPU_LE(	rev		x8, x8		)
 8:	next_ctr	v0
 	cbnz		x4, 99b
 
-0:	st1		{v0.16b}, [x5]
+	st1		{v0.16b}, [x5]
 	ldp		x29, x30, [sp], #16
 	ret
 
@@ -948,6 +948,9 @@ CPU_LE(	rev		x8, x8		)
 	 * If we are handling the tail of the input (x6 != NULL), return the
 	 * final keystream block back to the caller.
 	 */
+0:	cbz		x6, 8b
+	st1		{v0.16b}, [x6]
+	b		8b
 1:	cbz		x6, 8b
 	st1		{v1.16b}, [x6]
 	b		8b