lib/crypto: blake2: Provide functions for zeroizing blake2*_ctx structures

In certain cases crypto code needs to zeroize their local blake2b_ctx
or blake2s_ctx structures after use to avoid leaking sensitive material.
Provide blake2b_zeroize_ctx() and blake2s_zeroize_ctx() helper functions
that e.g. can be used with __cleanup() to automatically zeroize the
structures when they go out of scope.

While we're at it, replace the related memzero_explicit() calls in
lib/crypto/blake2*.c with calls to the new helper functions.

Signed-off-by: Thomas Huth <thuth@redhat.com>
Link: https://patch.msgid.link/20260916095022.604354-8-thuth@redhat.com
Signed-off-by: Eric Biggers <ebiggers@kernel.org>

include/crypto/blake2b.h

@@ -37,6 +37,15 @@ struct blake2b_ctx {
 	unsigned int outlen;
 };
 
+/**
+ * blake2b_zeroize_ctx() - Zeroize a blake2b_ctx structure
+ * @ctx: The blake2b_ctx to zeroize
+ */
+static inline void blake2b_zeroize_ctx(struct blake2b_ctx *ctx)
+{
+	memzero_explicit(ctx, sizeof(*ctx));
+}
+
 enum blake2b_iv {
 	BLAKE2B_IV0 = 0x6A09E667F3BCC908ULL,
 	BLAKE2B_IV1 = 0xBB67AE8584CAA73BULL,

include/crypto/blake2s.h

@@ -41,6 +41,15 @@ struct blake2s_ctx {
 	unsigned int outlen;
 };
 
+/**
+ * blake2s_zeroize_ctx() - Zeroize a blake2s_ctx structure
+ * @ctx: The blake2s_ctx to zeroize
+ */
+static inline void blake2s_zeroize_ctx(struct blake2s_ctx *ctx)
+{
+	memzero_explicit(ctx, sizeof(*ctx));
+}
+
 enum blake2s_iv {
 	BLAKE2S_IV0 = 0x6A09E667UL,
 	BLAKE2S_IV1 = 0xBB67AE85UL,

lib/crypto/blake2b.c

@@ -148,7 +148,7 @@ void blake2b_final(struct blake2b_ctx *ctx, u8 *out)
 	blake2b_compress(ctx, ctx->buf, 1, ctx->buflen);
 	cpu_to_le64_array(ctx->h, ARRAY_SIZE(ctx->h));
 	memcpy(out, ctx->h, ctx->outlen);
-	memzero_explicit(ctx, sizeof(*ctx));
+	blake2b_zeroize_ctx(ctx);
 }
 EXPORT_SYMBOL(blake2b_final);
 

lib/crypto/blake2s.c

@@ -142,7 +142,7 @@ void blake2s_final(struct blake2s_ctx *ctx, u8 *out)
 	blake2s_compress(ctx, ctx->buf, 1, ctx->buflen);
 	cpu_to_le32_array(ctx->h, ARRAY_SIZE(ctx->h));
 	memcpy(out, ctx->h, ctx->outlen);
-	memzero_explicit(ctx, sizeof(*ctx));
+	blake2s_zeroize_ctx(ctx);
 }
 EXPORT_SYMBOL(blake2s_final);