crypto: amlogic-gxl - permit async skcipher as fallback

Even though the amlogic-gxl 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@baylibre.com>
Signed-off-by: Herbert Xu <herbert@gondor.apana.org.au>

drivers/crypto/amlogic/amlogic-gxl.h

@@ -109,6 +109,7 @@ struct meson_dev {
 struct meson_cipher_req_ctx {
 	u32 op_dir;
 	int flow;
+	struct skcipher_request fallback_req;	// keep at the end
 };
 
 /*
@@ -126,7 +127,7 @@ struct meson_cipher_tfm_ctx {
 	u32 keylen;
 	u32 keymode;
 	struct meson_dev *mc;
-	struct crypto_sync_skcipher *fallback_tfm;
+	struct crypto_skcipher *fallback_tfm;
 };
 
 /*