Re: [PATCH] lib/crypto: blake2s: fix a CFI failure

["Jason A. Donenfeld" <Jason@zx2c4.com>]

The below kludge of a patch fixes the issue. Still unclear whether we
should go with something like this or get clang fixed or what.

diff --git a/arch/arm/crypto/blake2s-shash.c b/arch/arm/crypto/blake2s-shash.c
index 17c1c3bfe2f5..be8cde5f1719 100644
--- a/arch/arm/crypto/blake2s-shash.c
+++ b/arch/arm/crypto/blake2s-shash.c
@@ -13,12 +13,12 @@
 static int crypto_blake2s_update_arm(struct shash_desc *desc,
 				     const u8 *in, unsigned int inlen)
 {
-	return crypto_blake2s_update(desc, in, inlen, blake2s_compress);
+	return crypto_blake2s_update(desc, in, inlen);
 }

 static int crypto_blake2s_final_arm(struct shash_desc *desc, u8 *out)
 {
-	return crypto_blake2s_final(desc, out, blake2s_compress);
+	return crypto_blake2s_final(desc, out);
 }

 #define BLAKE2S_ALG(name, driver_name, digest_size)			\
diff --git a/arch/x86/crypto/blake2s-shash.c b/arch/x86/crypto/blake2s-shash.c
index f9e2fecdb761..c81ffedb4865 100644
--- a/arch/x86/crypto/blake2s-shash.c
+++ b/arch/x86/crypto/blake2s-shash.c
@@ -18,12 +18,12 @@
 static int crypto_blake2s_update_x86(struct shash_desc *desc,
 				     const u8 *in, unsigned int inlen)
 {
-	return crypto_blake2s_update(desc, in, inlen, blake2s_compress);
+	return crypto_blake2s_update(desc, in, inlen);
 }

 static int crypto_blake2s_final_x86(struct shash_desc *desc, u8 *out)
 {
-	return crypto_blake2s_final(desc, out, blake2s_compress);
+	return crypto_blake2s_final(desc, out);
 }

 #define BLAKE2S_ALG(name, driver_name, digest_size)			\
diff --git a/crypto/blake2s_generic.c b/crypto/blake2s_generic.c
index 72fe480f9bd6..050874588a84 100644
--- a/crypto/blake2s_generic.c
+++ b/crypto/blake2s_generic.c
@@ -5,6 +5,7 @@
  * Copyright (C) 2015-2019 Jason A. Donenfeld <Jason@zx2c4.com>. All
Rights Reserved.
  */

+#define FORCE_BLAKE2S_GENERIC
 #include <crypto/internal/blake2s.h>
 #include <crypto/internal/hash.h>

@@ -15,12 +16,12 @@
 static int crypto_blake2s_update_generic(struct shash_desc *desc,
 					 const u8 *in, unsigned int inlen)
 {
-	return crypto_blake2s_update(desc, in, inlen, blake2s_compress_generic);
+	return crypto_blake2s_update(desc, in, inlen);
 }

 static int crypto_blake2s_final_generic(struct shash_desc *desc, u8 *out)
 {
-	return crypto_blake2s_final(desc, out, blake2s_compress_generic);
+	return crypto_blake2s_final(desc, out);
 }

 #define BLAKE2S_ALG(name, driver_name, digest_size)			\
diff --git a/include/crypto/internal/blake2s.h
b/include/crypto/internal/blake2s.h
index d39cfa0d333e..fec7eead93fc 100644
--- a/include/crypto/internal/blake2s.h
+++ b/include/crypto/internal/blake2s.h
@@ -24,14 +24,14 @@ static inline void blake2s_set_lastblock(struct
blake2s_state *state)
 	state->f[0] = -1;
 }

-typedef void (*blake2s_compress_t)(struct blake2s_state *state,
-				   const u8 *block, size_t nblocks, u32 inc);
-
 /* Helper functions for BLAKE2s shared by the library and shash APIs */

+#ifdef FORCE_BLAKE2S_GENERIC
+#define blake2s_compress blake2s_compress_generic
+#endif
+
 static inline void __blake2s_update(struct blake2s_state *state,
-				    const u8 *in, size_t inlen,
-				    blake2s_compress_t compress)
+				    const u8 *in, size_t inlen)
 {
 	const size_t fill = BLAKE2S_BLOCK_SIZE - state->buflen;

@@ -39,7 +39,7 @@ static inline void __blake2s_update(struct
blake2s_state *state,
 		return;
 	if (inlen > fill) {
 		memcpy(state->buf + state->buflen, in, fill);
-		(*compress)(state, state->buf, 1, BLAKE2S_BLOCK_SIZE);
+		blake2s_compress(state, state->buf, 1, BLAKE2S_BLOCK_SIZE);
 		state->buflen = 0;
 		in += fill;
 		inlen -= fill;
@@ -47,7 +47,7 @@ static inline void __blake2s_update(struct
blake2s_state *state,
 	if (inlen > BLAKE2S_BLOCK_SIZE) {
 		const size_t nblocks = DIV_ROUND_UP(inlen, BLAKE2S_BLOCK_SIZE);
 		/* Hash one less (full) block than strictly possible */
-		(*compress)(state, in, nblocks - 1, BLAKE2S_BLOCK_SIZE);
+		blake2s_compress(state, in, nblocks - 1, BLAKE2S_BLOCK_SIZE);
 		in += BLAKE2S_BLOCK_SIZE * (nblocks - 1);
 		inlen -= BLAKE2S_BLOCK_SIZE * (nblocks - 1);
 	}
@@ -55,13 +55,12 @@ static inline void __blake2s_update(struct
blake2s_state *state,
 	state->buflen += inlen;
 }

-static inline void __blake2s_final(struct blake2s_state *state, u8 *out,
-				   blake2s_compress_t compress)
+static inline void __blake2s_final(struct blake2s_state *state, u8 *out)
 {
 	blake2s_set_lastblock(state);
 	memset(state->buf + state->buflen, 0,
 	       BLAKE2S_BLOCK_SIZE - state->buflen); /* Padding */
-	(*compress)(state, state->buf, 1, state->buflen);
+	blake2s_compress(state, state->buf, 1, state->buflen);
 	cpu_to_le32_array(state->h, ARRAY_SIZE(state->h));
 	memcpy(out, state->h, state->outlen);
 }
@@ -98,21 +97,19 @@ static inline int crypto_blake2s_init(struct
shash_desc *desc)
 }

 static inline int crypto_blake2s_update(struct shash_desc *desc,
-					const u8 *in, unsigned int inlen,
-					blake2s_compress_t compress)
+					const u8 *in, unsigned int inlen)
 {
 	struct blake2s_state *state = shash_desc_ctx(desc);

-	__blake2s_update(state, in, inlen, compress);
+	__blake2s_update(state, in, inlen);
 	return 0;
 }

-static inline int crypto_blake2s_final(struct shash_desc *desc, u8 *out,
-				       blake2s_compress_t compress)
+static inline int crypto_blake2s_final(struct shash_desc *desc, u8 *out)
 {
 	struct blake2s_state *state = shash_desc_ctx(desc);

-	__blake2s_final(state, out, compress);
+	__blake2s_final(state, out);
 	return 0;
 }

diff --git a/lib/crypto/blake2s.c b/lib/crypto/blake2s.c
index 9364f79937b8..a13f01ff53a7 100644
--- a/lib/crypto/blake2s.c
+++ b/lib/crypto/blake2s.c
@@ -18,14 +18,14 @@

 void blake2s_update(struct blake2s_state *state, const u8 *in, size_t inlen)
 {
-	__blake2s_update(state, in, inlen, blake2s_compress);
+	__blake2s_update(state, in, inlen);
 }
 EXPORT_SYMBOL(blake2s_update);

 void blake2s_final(struct blake2s_state *state, u8 *out)
 {
 	WARN_ON(IS_ENABLED(DEBUG) && !out);
-	__blake2s_final(state, out, blake2s_compress);
+	__blake2s_final(state, out);
 	memzero_explicit(state, sizeof(*state));
 }
 EXPORT_SYMBOL(blake2s_final);