crypto: arm64/aes - don't use IV buffer to return final keystream block

The arm64 bit sliced AES core code uses the IV buffer to pass the final
keystream block back to the glue code if the input is not a multiple of
the block size, so that the asm code does not have to deal with anything
except 16 byte blocks. This is done under the assumption that the outgoing
IV is meaningless anyway in this case, given that chaining is no longer
possible under these circumstances.

However, as it turns out, the CCM driver does expect the IV to retain
a value that is equal to the original IV except for the counter value,
and even interprets byte zero as a length indicator, which may result
in memory corruption if the IV is overwritten with something else.

So use a separate buffer to return the final keystream block.

Signed-off-by: Ard Biesheuvel <ard.biesheuvel@linaro.org>
Signed-off-by: Herbert Xu <herbert@gondor.apana.org.au>

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

@@ -853,13 +853,15 @@ ENDPROC(aesbs_xts_decrypt)
 
 	/*
 	 * aesbs_ctr_encrypt(u8 out[], u8 const in[], u8 const rk[],
-	 *		     int rounds, int blocks, u8 iv[], bool final)
+	 *		     int rounds, int blocks, u8 iv[], u8 final[])
 	 */
 ENTRY(aesbs_ctr_encrypt)
 	stp		x29, x30, [sp, #-16]!
 	mov		x29, sp
 
-	add		x4, x4, x6		// do one extra block if final
+	cmp		x6, #0
+	cset		x10, ne
+	add		x4, x4, x10		// do one extra block if final
 
 	ldp		x7, x8, [x5]
 	ld1		{v0.16b}, [x5]
@@ -874,19 +876,26 @@ CPU_LE(	rev		x8, x8		)
 	csel		x4, x4, xzr, pl
 	csel		x9, x9, xzr, le
 
+	tbnz		x9, #1, 0f
 	next_ctr	v1
+	tbnz		x9, #2, 0f
 	next_ctr	v2
+	tbnz		x9, #3, 0f
 	next_ctr	v3
+	tbnz		x9, #4, 0f
 	next_ctr	v4
+	tbnz		x9, #5, 0f
 	next_ctr	v5
+	tbnz		x9, #6, 0f
 	next_ctr	v6
+	tbnz		x9, #7, 0f
 	next_ctr	v7
 
 0:	mov		bskey, x2
 	mov		rounds, x3
 	bl		aesbs_encrypt8
 
-	lsr		x9, x9, x6		// disregard the extra block
+	lsr		x9, x9, x10		// disregard the extra block
 	tbnz		x9, #0, 0f
 
 	ld1		{v8.16b}, [x1], #16
@@ -928,36 +937,36 @@ CPU_LE(	rev		x8, x8		)
 	eor		v5.16b, v5.16b, v15.16b
 	st1		{v5.16b}, [x0], #16
 
-	next_ctr	v0
+8:	next_ctr	v0
 	cbnz		x4, 99b
 
 0:	st1		{v0.16b}, [x5]
-8:	ldp		x29, x30, [sp], #16
+	ldp		x29, x30, [sp], #16
 	ret
 
 	/*
-	 * If we are handling the tail of the input (x6 == 1), return the
-	 * final keystream block back to the caller via the IV buffer.
+	 * If we are handling the tail of the input (x6 != NULL), return the
+	 * final keystream block back to the caller.
 	 */
 1:	cbz		x6, 8b
-	st1		{v1.16b}, [x5]
+	st1		{v1.16b}, [x6]
 	b		8b
 2:	cbz		x6, 8b
-	st1		{v4.16b}, [x5]
+	st1		{v4.16b}, [x6]
 	b		8b
 3:	cbz		x6, 8b
-	st1		{v6.16b}, [x5]
+	st1		{v6.16b}, [x6]
 	b		8b
 4:	cbz		x6, 8b
-	st1		{v3.16b}, [x5]
+	st1		{v3.16b}, [x6]
 	b		8b
 5:	cbz		x6, 8b
-	st1		{v7.16b}, [x5]
+	st1		{v7.16b}, [x6]
 	b		8b
 6:	cbz		x6, 8b
-	st1		{v2.16b}, [x5]
+	st1		{v2.16b}, [x6]
 	b		8b
 7:	cbz		x6, 8b
-	st1		{v5.16b}, [x5]
+	st1		{v5.16b}, [x6]
 	b		8b
 ENDPROC(aesbs_ctr_encrypt)

arch/arm64/crypto/aes-neonbs-glue.c

@@ -34,7 +34,7 @@ asmlinkage void aesbs_cbc_decrypt(u8 out[], u8 const in[], u8 const rk[],
 				  int rounds, int blocks, u8 iv[]);
 
 asmlinkage void aesbs_ctr_encrypt(u8 out[], u8 const in[], u8 const rk[],
-				  int rounds, int blocks, u8 iv[], bool final);
+				  int rounds, int blocks, u8 iv[], u8 final[]);
 
 asmlinkage void aesbs_xts_encrypt(u8 out[], u8 const in[], u8 const rk[],
 				  int rounds, int blocks, u8 iv[]);
@@ -201,6 +201,7 @@ static int ctr_encrypt(struct skcipher_request *req)
 	struct crypto_skcipher *tfm = crypto_skcipher_reqtfm(req);
 	struct aesbs_ctx *ctx = crypto_skcipher_ctx(tfm);
 	struct skcipher_walk walk;
+	u8 buf[AES_BLOCK_SIZE];
 	int err;
 
 	err = skcipher_walk_virt(&walk, req, true);
@@ -208,12 +209,12 @@ static int ctr_encrypt(struct skcipher_request *req)
 	kernel_neon_begin();
 	while (walk.nbytes > 0) {
 		unsigned int blocks = walk.nbytes / AES_BLOCK_SIZE;
-		bool final = (walk.total % AES_BLOCK_SIZE) != 0;
+		u8 *final = (walk.total % AES_BLOCK_SIZE) ? buf : NULL;
 
 		if (walk.nbytes < walk.total) {
 			blocks = round_down(blocks,
 					    walk.stride / AES_BLOCK_SIZE);
-			final = false;
+			final = NULL;
 		}
 
 		aesbs_ctr_encrypt(walk.dst.virt.addr, walk.src.virt.addr,
@@ -225,7 +226,7 @@ static int ctr_encrypt(struct skcipher_request *req)
 
 			if (dst != src)
 				memcpy(dst, src, walk.total % AES_BLOCK_SIZE);
-			crypto_xor(dst, walk.iv, walk.total % AES_BLOCK_SIZE);
+			crypto_xor(dst, final, walk.total % AES_BLOCK_SIZE);
 
 			err = skcipher_walk_done(&walk, 0);
 			break;