crypto: arm/aes-neonbs - resolve fallback cipher at runtime

Currently, the bit sliced NEON AES code for ARM has a link time
dependency on the scalar ARM asm implementation, which it uses as a
fallback to perform CBC encryption and the encryption of the initial
XTS tweak.

The bit sliced NEON code is both fast and time invariant, which makes
it a reasonable default on hardware that supports it. However, the
ARM asm code it pulls in is not time invariant, and due to the way it
is linked in, cannot be overridden by the new generic time invariant
driver. In fact, it will not be used at all, given that the ARM asm
code registers itself as a cipher with a priority that exceeds the
priority of the fixed time cipher.

So remove the link time dependency, and allocate the fallback cipher
via the crypto API. Note that this requires this driver's module_init
call to be replaced with late_initcall, so that the (possibly generic)
fallback cipher is guaranteed to be available when the builtin test
is performed at registration time.

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

arch/arm/crypto/Kconfig

···
 	depends on KERNEL_MODE_NEON
 	select CRYPTO_BLKCIPHER
 	select CRYPTO_SIMD
-	select CRYPTO_AES_ARM
+	select CRYPTO_AES
 	help
 	  Use a faster and more secure NEON based implementation of AES in CBC,
 	  CTR and XTS modes

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

···
 asmlinkage void aesbs_xts_decrypt(u8 out[], u8 const in[], u8 const rk[],
 				  int rounds, int blocks, u8 iv[]);
 
-asmlinkage void __aes_arm_encrypt(const u32 rk[], int rounds, const u8 in[],
-				  u8 out[]);
-
 struct aesbs_ctx {
 	int	rounds;
 	u8	rk[13 * (8 * AES_BLOCK_SIZE) + 32] __aligned(AES_BLOCK_SIZE);
···
 
 struct aesbs_cbc_ctx {
 	struct aesbs_ctx	key;
-	u32			enc[AES_MAX_KEYLENGTH_U32];
+	struct crypto_cipher	*enc_tfm;
 };
 
 struct aesbs_xts_ctx {
 	struct aesbs_ctx	key;
-	u32			twkey[AES_MAX_KEYLENGTH_U32];
+	struct crypto_cipher	*tweak_tfm;
 };
 
 static int aesbs_setkey(struct crypto_skcipher *tfm, const u8 *in_key,
···
 
 	ctx->key.rounds = 6 + key_len / 4;
 
-	memcpy(ctx->enc, rk.key_enc, sizeof(ctx->enc));
-
 	kernel_neon_begin();
 	aesbs_convert_key(ctx->key.rk, rk.key_enc, ctx->key.rounds);
 	kernel_neon_end();
 
-	return 0;
+	return crypto_cipher_setkey(ctx->enc_tfm, in_key, key_len);
 }
 
 static void cbc_encrypt_one(struct crypto_skcipher *tfm, const u8 *src, u8 *dst)
 {
 	struct aesbs_cbc_ctx *ctx = crypto_skcipher_ctx(tfm);
 
-	__aes_arm_encrypt(ctx->enc, ctx->key.rounds, src, dst);
+	crypto_cipher_encrypt_one(ctx->enc_tfm, dst, src);
 }
 
 static int cbc_encrypt(struct skcipher_request *req)
···
 	kernel_neon_end();
 
 	return err;
+}
+
+static int cbc_init(struct crypto_tfm *tfm)
+{
+	struct aesbs_cbc_ctx *ctx = crypto_tfm_ctx(tfm);
+
+	ctx->enc_tfm = crypto_alloc_cipher("aes", 0, 0);
+	if (IS_ERR(ctx->enc_tfm))
+		return PTR_ERR(ctx->enc_tfm);
+	return 0;
+}
+
+static void cbc_exit(struct crypto_tfm *tfm)
+{
+	struct aesbs_cbc_ctx *ctx = crypto_tfm_ctx(tfm);
+
+	crypto_free_cipher(ctx->enc_tfm);
 }
 
 static int ctr_encrypt(struct skcipher_request *req)
···
 			    unsigned int key_len)
 {
 	struct aesbs_xts_ctx *ctx = crypto_skcipher_ctx(tfm);
-	struct crypto_aes_ctx rk;
 	int err;
 
 	err = xts_verify_key(tfm, in_key, key_len);
···
 		return err;
 
 	key_len /= 2;
-	err = crypto_aes_expand_key(&rk, in_key + key_len, key_len);
+	err = crypto_cipher_setkey(ctx->tweak_tfm, in_key + key_len, key_len);
 	if (err)
 		return err;
 
-	memcpy(ctx->twkey, rk.key_enc, sizeof(ctx->twkey));
-
 	return aesbs_setkey(tfm, in_key, key_len);
+}
+
+static int xts_init(struct crypto_tfm *tfm)
+{
+	struct aesbs_xts_ctx *ctx = crypto_tfm_ctx(tfm);
+
+	ctx->tweak_tfm = crypto_alloc_cipher("aes", 0, 0);
+	if (IS_ERR(ctx->tweak_tfm))
+		return PTR_ERR(ctx->tweak_tfm);
+	return 0;
+}
+
+static void xts_exit(struct crypto_tfm *tfm)
+{
+	struct aesbs_xts_ctx *ctx = crypto_tfm_ctx(tfm);
+
+	crypto_free_cipher(ctx->tweak_tfm);
 }
 
 static int __xts_crypt(struct skcipher_request *req,
···
 
 	err = skcipher_walk_virt(&walk, req, true);
 
-	__aes_arm_encrypt(ctx->twkey, ctx->key.rounds, walk.iv, walk.iv);
+	crypto_cipher_encrypt_one(ctx->tweak_tfm, walk.iv, walk.iv);
 
 	kernel_neon_begin();
 	while (walk.nbytes >= AES_BLOCK_SIZE) {
···
 	.base.cra_ctxsize	= sizeof(struct aesbs_cbc_ctx),
 	.base.cra_module	= THIS_MODULE,
 	.base.cra_flags		= CRYPTO_ALG_INTERNAL,
+	.base.cra_init		= cbc_init,
+	.base.cra_exit		= cbc_exit,
 
 	.min_keysize		= AES_MIN_KEY_SIZE,
 	.max_keysize		= AES_MAX_KEY_SIZE,
···
 	.base.cra_ctxsize	= sizeof(struct aesbs_xts_ctx),
 	.base.cra_module	= THIS_MODULE,
 	.base.cra_flags		= CRYPTO_ALG_INTERNAL,
+	.base.cra_init		= xts_init,
+	.base.cra_exit		= xts_exit,
 
 	.min_keysize		= 2 * AES_MIN_KEY_SIZE,
 	.max_keysize		= 2 * AES_MAX_KEY_SIZE,
···
 	return err;
 }
 
-module_init(aes_init);
+late_initcall(aes_init);
 module_exit(aes_exit);