crypto: sun4i - permit asynchronous skcipher as fallback

Even though the sun4i driver implements asynchronous versions of ecb(aes)
and cbc(aes), the fallbacks it allocates are required to be synchronous.
Given that SIMD based software implementations are usually asynchronous
as well, even though they rarely complete asynchronously (this typically
only happens in cases where the request was made from softirq context,
while SIMD was already in use in the task context that it interrupted),
these implementations are disregarded, and either the generic C version
or another table based version implemented in assembler is selected
instead.

Since falling back to synchronous AES is not only a performance issue, but
potentially a security issue as well (due to the fact that table based AES
is not time invariant), let's fix this, by allocating an ordinary skcipher
as the fallback, and invoke it with the completion routine that was given
to the outer request.
Signed-off-by: Ard Biesheuvel <ardb@kernel.org>
Tested-by: Corentin Labbe <clabbe.montjoie@gmail.com>
Signed-off-by: Herbert Xu <herbert@gondor.apana.org.au>

drivers/crypto/allwinner/sun4i-ss/sun4i-ss-cipher.c

@@ -122,19 +122,17 @@ static int noinline_for_stack sun4i_ss_cipher_poll_fallback(struct skcipher_requ
 	struct crypto_skcipher *tfm = crypto_skcipher_reqtfm(areq);
 	struct sun4i_tfm_ctx *op = crypto_skcipher_ctx(tfm);
 	struct sun4i_cipher_req_ctx *ctx = skcipher_request_ctx(areq);
-	SYNC_SKCIPHER_REQUEST_ON_STACK(subreq, op->fallback_tfm);
 	int err;
 
-	skcipher_request_set_sync_tfm(subreq, op->fallback_tfm);
-	skcipher_request_set_callback(subreq, areq->base.flags, NULL,
-				      NULL);
-	skcipher_request_set_crypt(subreq, areq->src, areq->dst,
+	skcipher_request_set_tfm(&ctx->fallback_req, op->fallback_tfm);
+	skcipher_request_set_callback(&ctx->fallback_req, areq->base.flags,
+				      areq->base.complete, areq->base.data);
+	skcipher_request_set_crypt(&ctx->fallback_req, areq->src, areq->dst,
 				   areq->cryptlen, areq->iv);
 	if (ctx->mode & SS_DECRYPTION)
-		err = crypto_skcipher_decrypt(subreq);
+		err = crypto_skcipher_decrypt(&ctx->fallback_req);
 	else
-		err = crypto_skcipher_encrypt(subreq);
-	skcipher_request_zero(subreq);
+		err = crypto_skcipher_encrypt(&ctx->fallback_req);
 
 	return err;
 }
@@ -494,23 +492,25 @@ int sun4i_ss_cipher_init(struct crypto_tfm *tfm)
 			    alg.crypto.base);
 	op->ss = algt->ss;
 
-	crypto_skcipher_set_reqsize(__crypto_skcipher_cast(tfm),
-				    sizeof(struct sun4i_cipher_req_ctx));
-
-	op->fallback_tfm = crypto_alloc_sync_skcipher(name, 0, CRYPTO_ALG_NEED_FALLBACK);
+	op->fallback_tfm = crypto_alloc_skcipher(name, 0, CRYPTO_ALG_NEED_FALLBACK);
 	if (IS_ERR(op->fallback_tfm)) {
 		dev_err(op->ss->dev, "ERROR: Cannot allocate fallback for %s %ld\n",
 			name, PTR_ERR(op->fallback_tfm));
 		return PTR_ERR(op->fallback_tfm);
 	}
 
+	crypto_skcipher_set_reqsize(__crypto_skcipher_cast(tfm),
+				    sizeof(struct sun4i_cipher_req_ctx) +
+				    crypto_skcipher_reqsize(op->fallback_tfm));
+
+
 	err = pm_runtime_get_sync(op->ss->dev);
 	if (err < 0)
 		goto error_pm;
 
 	return 0;
 error_pm:
-	crypto_free_sync_skcipher(op->fallback_tfm);
+	crypto_free_skcipher(op->fallback_tfm);
 	return err;
 }
 
@@ -518,7 +518,7 @@ void sun4i_ss_cipher_exit(struct crypto_tfm *tfm)
 {
 	struct sun4i_tfm_ctx *op = crypto_tfm_ctx(tfm);
 
-	crypto_free_sync_skcipher(op->fallback_tfm);
+	crypto_free_skcipher(op->fallback_tfm);
 	pm_runtime_put(op->ss->dev);
 }
 
@@ -546,10 +546,10 @@ int sun4i_ss_aes_setkey(struct crypto_skcipher *tfm, const u8 *key,
 	op->keylen = keylen;
 	memcpy(op->key, key, keylen);
 
-	crypto_sync_skcipher_clear_flags(op->fallback_tfm, CRYPTO_TFM_REQ_MASK);
-	crypto_sync_skcipher_set_flags(op->fallback_tfm, tfm->base.crt_flags & CRYPTO_TFM_REQ_MASK);
+	crypto_skcipher_clear_flags(op->fallback_tfm, CRYPTO_TFM_REQ_MASK);
+	crypto_skcipher_set_flags(op->fallback_tfm, tfm->base.crt_flags & CRYPTO_TFM_REQ_MASK);
 
-	return crypto_sync_skcipher_setkey(op->fallback_tfm, key, keylen);
+	return crypto_skcipher_setkey(op->fallback_tfm, key, keylen);
 }
 
 /* check and set the DES key, prepare the mode to be used */
@@ -566,10 +566,10 @@ int sun4i_ss_des_setkey(struct crypto_skcipher *tfm, const u8 *key,
 	op->keylen = keylen;
 	memcpy(op->key, key, keylen);
 
-	crypto_sync_skcipher_clear_flags(op->fallback_tfm, CRYPTO_TFM_REQ_MASK);
-	crypto_sync_skcipher_set_flags(op->fallback_tfm, tfm->base.crt_flags & CRYPTO_TFM_REQ_MASK);
+	crypto_skcipher_clear_flags(op->fallback_tfm, CRYPTO_TFM_REQ_MASK);
+	crypto_skcipher_set_flags(op->fallback_tfm, tfm->base.crt_flags & CRYPTO_TFM_REQ_MASK);
 
-	return crypto_sync_skcipher_setkey(op->fallback_tfm, key, keylen);
+	return crypto_skcipher_setkey(op->fallback_tfm, key, keylen);
 }
 
 /* check and set the 3DES key, prepare the mode to be used */
@@ -586,9 +586,9 @@ int sun4i_ss_des3_setkey(struct crypto_skcipher *tfm, const u8 *key,
 	op->keylen = keylen;
 	memcpy(op->key, key, keylen);
 
-	crypto_sync_skcipher_clear_flags(op->fallback_tfm, CRYPTO_TFM_REQ_MASK);
-	crypto_sync_skcipher_set_flags(op->fallback_tfm, tfm->base.crt_flags & CRYPTO_TFM_REQ_MASK);
+	crypto_skcipher_clear_flags(op->fallback_tfm, CRYPTO_TFM_REQ_MASK);
+	crypto_skcipher_set_flags(op->fallback_tfm, tfm->base.crt_flags & CRYPTO_TFM_REQ_MASK);
 
-	return crypto_sync_skcipher_setkey(op->fallback_tfm, key, keylen);
+	return crypto_skcipher_setkey(op->fallback_tfm, key, keylen);
 
 }

drivers/crypto/allwinner/sun4i-ss/sun4i-ss.h

@@ -170,11 +170,12 @@ struct sun4i_tfm_ctx {
 	u32 keylen;
 	u32 keymode;
 	struct sun4i_ss_ctx *ss;
-	struct crypto_sync_skcipher *fallback_tfm;
+	struct crypto_skcipher *fallback_tfm;
 };
 
 struct sun4i_cipher_req_ctx {
 	u32 mode;
+	struct skcipher_request fallback_req;   // keep at the end
 };
 
 struct sun4i_req_ctx {