crypto: skcipher - Introduce crypto_sync_skcipher

In preparation for removal of VLAs due to skcipher requests on the stack
via SKCIPHER_REQUEST_ON_STACK() usage, this introduces the infrastructure
for the "sync skcipher" tfm, which is for handling the on-stack cases of
skcipher, which are always non-ASYNC and have a known limited request
size.

The crypto API additions:

	struct crypto_sync_skcipher (wrapper for struct crypto_skcipher)
	crypto_alloc_sync_skcipher()
	crypto_free_sync_skcipher()
	crypto_sync_skcipher_setkey()
	crypto_sync_skcipher_get_flags()
	crypto_sync_skcipher_set_flags()
	crypto_sync_skcipher_clear_flags()
	crypto_sync_skcipher_blocksize()
	crypto_sync_skcipher_ivsize()
	crypto_sync_skcipher_reqtfm()
	skcipher_request_set_sync_tfm()
	SYNC_SKCIPHER_REQUEST_ON_STACK() (with tfm type check)

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

crypto/skcipher.c

@@ -949,6 +949,30 @@ struct crypto_skcipher *crypto_alloc_skcipher(const char *alg_name,
 }
 EXPORT_SYMBOL_GPL(crypto_alloc_skcipher);
 
+struct crypto_sync_skcipher *crypto_alloc_sync_skcipher(
+				const char *alg_name, u32 type, u32 mask)
+{
+	struct crypto_skcipher *tfm;
+
+	/* Only sync algorithms allowed. */
+	mask |= CRYPTO_ALG_ASYNC;
+
+	tfm = crypto_alloc_tfm(alg_name, &crypto_skcipher_type2, type, mask);
+
+	/*
+	 * Make sure we do not allocate something that might get used with
+	 * an on-stack request: check the request size.
+	 */
+	if (!IS_ERR(tfm) && WARN_ON(crypto_skcipher_reqsize(tfm) >
+				    MAX_SYNC_SKCIPHER_REQSIZE)) {
+		crypto_free_skcipher(tfm);
+		return ERR_PTR(-EINVAL);
+	}
+
+	return (struct crypto_sync_skcipher *)tfm;
+}
+EXPORT_SYMBOL_GPL(crypto_alloc_sync_skcipher);
+
 int crypto_has_skcipher2(const char *alg_name, u32 type, u32 mask)
 {
 	return crypto_type_has_alg(alg_name, &crypto_skcipher_type2,

include/crypto/skcipher.h

@@ -65,6 +65,10 @@ struct crypto_skcipher {
 	struct crypto_tfm base;
 };
 
+struct crypto_sync_skcipher {
+	struct crypto_skcipher base;
+};
+
 /**
  * struct skcipher_alg - symmetric key cipher definition
  * @min_keysize: Minimum key size supported by the transformation. This is the
@@ -139,6 +143,19 @@ struct skcipher_alg {
 	struct crypto_alg base;
 };
 
+#define MAX_SYNC_SKCIPHER_REQSIZE      384
+/*
+ * This performs a type-check against the "tfm" argument to make sure
+ * all users have the correct skcipher tfm for doing on-stack requests.
+ */
+#define SYNC_SKCIPHER_REQUEST_ON_STACK(name, tfm) \
+	char __##name##_desc[sizeof(struct skcipher_request) + \
+			     MAX_SYNC_SKCIPHER_REQSIZE + \
+			     (!(sizeof((struct crypto_sync_skcipher *)1 == \
+				       (typeof(tfm))1))) \
+			    ] CRYPTO_MINALIGN_ATTR; \
+	struct skcipher_request *name = (void *)__##name##_desc
+
 #define SKCIPHER_REQUEST_ON_STACK(name, tfm) \
 	char __##name##_desc[sizeof(struct skcipher_request) + \
 		crypto_skcipher_reqsize(tfm)] CRYPTO_MINALIGN_ATTR; \
@@ -197,6 +214,9 @@ static inline struct crypto_skcipher *__crypto_skcipher_cast(
 struct crypto_skcipher *crypto_alloc_skcipher(const char *alg_name,
 					      u32 type, u32 mask);
 
+struct crypto_sync_skcipher *crypto_alloc_sync_skcipher(const char *alg_name,
+					      u32 type, u32 mask);
+
 static inline struct crypto_tfm *crypto_skcipher_tfm(
 	struct crypto_skcipher *tfm)
 {
@@ -212,6 +232,11 @@ static inline void crypto_free_skcipher(struct crypto_skcipher *tfm)
 	crypto_destroy_tfm(tfm, crypto_skcipher_tfm(tfm));
 }
 
+static inline void crypto_free_sync_skcipher(struct crypto_sync_skcipher *tfm)
+{
+	crypto_free_skcipher(&tfm->base);
+}
+
 /**
  * crypto_has_skcipher() - Search for the availability of an skcipher.
  * @alg_name: is the cra_name / name or cra_driver_name / driver name of the
@@ -280,6 +305,12 @@ static inline unsigned int crypto_skcipher_ivsize(struct crypto_skcipher *tfm)
 	return tfm->ivsize;
 }
 
+static inline unsigned int crypto_sync_skcipher_ivsize(
+	struct crypto_sync_skcipher *tfm)
+{
+	return crypto_skcipher_ivsize(&tfm->base);
+}
+
 static inline unsigned int crypto_skcipher_alg_chunksize(
 	struct skcipher_alg *alg)
 {
@@ -356,6 +387,12 @@ static inline unsigned int crypto_skcipher_blocksize(
 	return crypto_tfm_alg_blocksize(crypto_skcipher_tfm(tfm));
 }
 
+static inline unsigned int crypto_sync_skcipher_blocksize(
+	struct crypto_sync_skcipher *tfm)
+{
+	return crypto_skcipher_blocksize(&tfm->base);
+}
+
 static inline unsigned int crypto_skcipher_alignmask(
 	struct crypto_skcipher *tfm)
 {
@@ -379,6 +416,24 @@ static inline void crypto_skcipher_clear_flags(struct crypto_skcipher *tfm,
 	crypto_tfm_clear_flags(crypto_skcipher_tfm(tfm), flags);
 }
 
+static inline u32 crypto_sync_skcipher_get_flags(
+	struct crypto_sync_skcipher *tfm)
+{
+	return crypto_skcipher_get_flags(&tfm->base);
+}
+
+static inline void crypto_sync_skcipher_set_flags(
+	struct crypto_sync_skcipher *tfm, u32 flags)
+{
+	crypto_skcipher_set_flags(&tfm->base, flags);
+}
+
+static inline void crypto_sync_skcipher_clear_flags(
+	struct crypto_sync_skcipher *tfm, u32 flags)
+{
+	crypto_skcipher_clear_flags(&tfm->base, flags);
+}
+
 /**
  * crypto_skcipher_setkey() - set key for cipher
  * @tfm: cipher handle
@@ -401,6 +456,12 @@ static inline int crypto_skcipher_setkey(struct crypto_skcipher *tfm,
 	return tfm->setkey(tfm, key, keylen);
 }
 
+static inline int crypto_sync_skcipher_setkey(struct crypto_sync_skcipher *tfm,
+					 const u8 *key, unsigned int keylen)
+{
+	return crypto_skcipher_setkey(&tfm->base, key, keylen);
+}
+
 static inline unsigned int crypto_skcipher_default_keysize(
 	struct crypto_skcipher *tfm)
 {
@@ -422,6 +483,14 @@ static inline struct crypto_skcipher *crypto_skcipher_reqtfm(
 	return __crypto_skcipher_cast(req->base.tfm);
 }
 
+static inline struct crypto_sync_skcipher *crypto_sync_skcipher_reqtfm(
+	struct skcipher_request *req)
+{
+	struct crypto_skcipher *tfm = crypto_skcipher_reqtfm(req);
+
+	return container_of(tfm, struct crypto_sync_skcipher, base);
+}
+
 /**
  * crypto_skcipher_encrypt() - encrypt plaintext
  * @req: reference to the skcipher_request handle that holds all information
@@ -500,6 +569,12 @@ static inline void skcipher_request_set_tfm(struct skcipher_request *req,
 	req->base.tfm = crypto_skcipher_tfm(tfm);
 }
 
+static inline void skcipher_request_set_sync_tfm(struct skcipher_request *req,
+					    struct crypto_sync_skcipher *tfm)
+{
+	skcipher_request_set_tfm(req, &tfm->base);
+}
+
 static inline struct skcipher_request *skcipher_request_cast(
 	struct crypto_async_request *req)
 {