crypto: arm/aes-neonbs - implement ciphertext stealing for XTS

Update the AES-XTS implementation based on NEON instructions so that it
can deal with inputs whose size is not a multiple of the cipher block
size. This is part of the original XTS specification, but was never
implemented before in the Linux kernel.

Signed-off-by: Ard Biesheuvel <[e-mail]>
Signed-off-by: Herbert Xu <[e-mail]>

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

···
 
 	/*
 	 * aesbs_xts_encrypt(u8 out[], u8 const in[], u8 const rk[], int rounds,
-	 *		     int blocks, u8 iv[])
+	 *		     int blocks, u8 iv[], int reorder_last_tweak)
 	 * aesbs_xts_decrypt(u8 out[], u8 const in[], u8 const rk[], int rounds,
-	 *		     int blocks, u8 iv[])
+	 *		     int blocks, u8 iv[], int reorder_last_tweak)
 	 */
 __xts_prepare8:
 	vld1.8		{q14}, [r7]		// load iv
···
 
 	vld1.8		{q7}, [r1]!
 	next_tweak	q14, q12, q15, q13
-	veor		q7, q7, q12
+THUMB(	itt		le		)
+	W(cmple)	r8, #0
+	ble		1f
+0:	veor		q7, q7, q12
 	vst1.8		{q12}, [r4, :128]
 
-0:	vst1.8		{q14}, [r7]		// store next iv
+	vst1.8		{q14}, [r7]		// store next iv
 	bx		lr
+
+1:	vswp		q12, q14
+	b		0b
 ENDPROC(__xts_prepare8)
 
 	.macro		__xts_crypt, do8, o0, o1, o2, o3, o4, o5, o6, o7
 	push		{r4-r8, lr}
 	mov		r5, sp			// preserve sp
 	ldrd		r6, r7, [sp, #24]	// get blocks and iv args
+	ldr		r8, [sp, #32]		// reorder final tweak?
+	rsb		r8, r8, #1
 	sub		ip, sp, #128		// make room for 8x tweak
 	bic		ip, ip, #0xf		// align sp to 16 bytes
 	mov		sp, ip

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

···
 #include <crypto/ctr.h>
 #include <crypto/internal/simd.h>
 #include <crypto/internal/skcipher.h>
+#include <crypto/scatterwalk.h>
 #include <crypto/xts.h>
 #include <linux/module.h>
 
···
 				  int rounds, int blocks, u8 ctr[], u8 final[]);
 
 asmlinkage void aesbs_xts_encrypt(u8 out[], u8 const in[], u8 const rk[],
-				  int rounds, int blocks, u8 iv[]);
+				  int rounds, int blocks, u8 iv[], int);
 asmlinkage void aesbs_xts_decrypt(u8 out[], u8 const in[], u8 const rk[],
-				  int rounds, int blocks, u8 iv[]);
+				  int rounds, int blocks, u8 iv[], int);
 
 struct aesbs_ctx {
 	int	rounds;
···
 
 struct aesbs_xts_ctx {
 	struct aesbs_ctx	key;
+	struct crypto_cipher	*cts_tfm;
 	struct crypto_cipher	*tweak_tfm;
 };
 
···
 		return err;
 
 	key_len /= 2;
+	err = crypto_cipher_setkey(ctx->cts_tfm, in_key, key_len);
+	if (err)
+		return err;
 	err = crypto_cipher_setkey(ctx->tweak_tfm, in_key + key_len, key_len);
 	if (err)
 		return err;
···
 {
 	struct aesbs_xts_ctx *ctx = crypto_tfm_ctx(tfm);
 
+	ctx->cts_tfm = crypto_alloc_cipher("aes", 0, 0);
+	if (IS_ERR(ctx->cts_tfm))
+		return PTR_ERR(ctx->cts_tfm);
+
 	ctx->tweak_tfm = crypto_alloc_cipher("aes", 0, 0);
+	if (IS_ERR(ctx->tweak_tfm))
+		crypto_free_cipher(ctx->cts_tfm);
 
 	return PTR_ERR_OR_ZERO(ctx->tweak_tfm);
 }
···
 	struct aesbs_xts_ctx *ctx = crypto_tfm_ctx(tfm);
 
 	crypto_free_cipher(ctx->tweak_tfm);
+	crypto_free_cipher(ctx->cts_tfm);
 }
 
-static int __xts_crypt(struct skcipher_request *req,
+static int __xts_crypt(struct skcipher_request *req, bool encrypt,
 		       void (*fn)(u8 out[], u8 const in[], u8 const rk[],
-				  int rounds, int blocks, u8 iv[]))
+				  int rounds, int blocks, u8 iv[], int))
 {
 	struct crypto_skcipher *tfm = crypto_skcipher_reqtfm(req);
 	struct aesbs_xts_ctx *ctx = crypto_skcipher_ctx(tfm);
+	int tail = req->cryptlen % AES_BLOCK_SIZE;
+	struct skcipher_request subreq;
+	u8 buf[2 * AES_BLOCK_SIZE];
 	struct skcipher_walk walk;
 	int err;
+
+	if (req->cryptlen < AES_BLOCK_SIZE)
+		return -EINVAL;
+
+	if (unlikely(tail)) {
+		skcipher_request_set_tfm(&subreq, tfm);
+		skcipher_request_set_callback(&subreq,
+					      skcipher_request_flags(req),
+					      NULL, NULL);
+		skcipher_request_set_crypt(&subreq, req->src, req->dst,
+					   req->cryptlen - tail, req->iv);
+		req = &subreq;
+	}
 
 	err = skcipher_walk_virt(&walk, req, true);
 	if (err)
···
 
 	while (walk.nbytes >= AES_BLOCK_SIZE) {
 		unsigned int blocks = walk.nbytes / AES_BLOCK_SIZE;
+		int reorder_last_tweak = !encrypt && tail > 0;
 
-		if (walk.nbytes < walk.total)
+		if (walk.nbytes < walk.total) {
 			blocks = round_down(blocks,
 					    walk.stride / AES_BLOCK_SIZE);
+			reorder_last_tweak = 0;
+		}
 
 		kernel_neon_begin();
 		fn(walk.dst.virt.addr, walk.src.virt.addr, ctx->key.rk,
-		   ctx->key.rounds, blocks, walk.iv);
+		   ctx->key.rounds, blocks, walk.iv, reorder_last_tweak);
 		kernel_neon_end();
 		err = skcipher_walk_done(&walk,
 					 walk.nbytes - blocks * AES_BLOCK_SIZE);
 	}
 
-	return err;
+	if (err || likely(!tail))
+		return err;
+
+	/* handle ciphertext stealing */
+	scatterwalk_map_and_copy(buf, req->dst, req->cryptlen - AES_BLOCK_SIZE,
+				 AES_BLOCK_SIZE, 0);
+	memcpy(buf + AES_BLOCK_SIZE, buf, tail);
+	scatterwalk_map_and_copy(buf, req->src, req->cryptlen, tail, 0);
+
+	crypto_xor(buf, req->iv, AES_BLOCK_SIZE);
+
+	if (encrypt)
+		crypto_cipher_encrypt_one(ctx->cts_tfm, buf, buf);
+	else
+		crypto_cipher_decrypt_one(ctx->cts_tfm, buf, buf);
+
+	crypto_xor(buf, req->iv, AES_BLOCK_SIZE);
+
+	scatterwalk_map_and_copy(buf, req->dst, req->cryptlen - AES_BLOCK_SIZE,
+				 AES_BLOCK_SIZE + tail, 1);
+	return 0;
 }
 
 static int xts_encrypt(struct skcipher_request *req)
 {
-	return __xts_crypt(req, aesbs_xts_encrypt);
+	return __xts_crypt(req, true, aesbs_xts_encrypt);
 }
 
 static int xts_decrypt(struct skcipher_request *req)
 {
-	return __xts_crypt(req, aesbs_xts_decrypt);
+	return __xts_crypt(req, false, aesbs_xts_decrypt);
 }
 
 static struct skcipher_alg aes_algs[] = { {