[PATCH] lib: rsa: function to verify a signature against a hash

[Heiko Stuebner]

From: Heiko Stuebner <heiko.stuebner at theobroma-systems.com>

rsa_verify() expects a memory region and wants to do the hashing itself,
but there may be cases where the hashing is done via other means,
like hashing a squashfs rootfs.

So add rsa_verify_hash() to allow verifiying a signature against
an existing hash. As this entails the same verification routines
we can just move the relevant code over from rsa_verify() and also
call rsa_verify_hash() from there.

Signed-off-by: Heiko Stuebner <heiko.stuebner at theobroma-systems.com>
---
Patch depends on at least 
lib: rsa: take spl/non-spl into account when building rsa_verify_with_pkey()

 include/u-boot/rsa.h | 21 +++++++++++++++++
 lib/rsa/rsa-verify.c | 56 +++++++++++++++++++++++++-------------------
 2 files changed, 53 insertions(+), 24 deletions(-)

diff --git a/include/u-boot/rsa.h b/include/u-boot/rsa.h
index 2d3024d8b7..a0bae495f0 100644
--- a/include/u-boot/rsa.h
+++ b/include/u-boot/rsa.h
@@ -82,6 +82,20 @@ static inline int rsa_add_verify_data(struct image_sign_info *info,
 #endif
 
 #if IMAGE_ENABLE_VERIFY
+/**
+ * rsa_verify_hash() - Verify a signature against a hash
+ *
+ * Verify a RSA PKCS1.5 signature against an expected hash.
+ *
+ * @info:	Specifies key and FIT information
+ * @hash:	Hash according to algorithm specified in @info
+ * @sig:	Signature
+ * @sig_len:	Number of bytes in signature
+ * @return 0 if verified, -ve on error
+ */
+int rsa_verify_hash(struct image_sign_info *info,
+		    const uint8_t *hash, uint8_t *sig, uint sig_len);
+
 /**
  * rsa_verify() - Verify a signature against some data
  *
@@ -108,6 +122,13 @@ int padding_pss_verify(struct image_sign_info *info,
 		       const uint8_t *hash, int hash_len);
 #endif /* CONFIG_FIT_ENABLE_RSASSA_PSS_SUPPORT */
 #else
+static inline int rsa_verify_hash(struct image_sign_info *info,
+				  const uint8_t *hash,
+				  uint8_t *sig, uint sig_len)
+{
+	return -ENXIO;
+}
+
 static inline int rsa_verify(struct image_sign_info *info,
 		const struct image_region region[], int region_count,
 		uint8_t *sig, uint sig_len)
diff --git a/lib/rsa/rsa-verify.c b/lib/rsa/rsa-verify.c
index 61d98e6e2d..6c4bbc4625 100644
--- a/lib/rsa/rsa-verify.c
+++ b/lib/rsa/rsa-verify.c
@@ -478,33 +478,11 @@ static int rsa_verify_with_keynode(struct image_sign_info *info,
 }
 #endif
 
-int rsa_verify(struct image_sign_info *info,
-	       const struct image_region region[], int region_count,
-	       uint8_t *sig, uint sig_len)
+int rsa_verify_hash(struct image_sign_info *info,
+		    const uint8_t *hash, uint8_t *sig, uint sig_len)
 {
-	/* Reserve memory for maximum checksum-length */
-	uint8_t hash[info->crypto->key_len];
 	int ret = -EACCES;
 
-	/*
-	 * Verify that the checksum-length does not exceed the
-	 * rsa-signature-length
-	 */
-	if (info->checksum->checksum_len >
-	    info->crypto->key_len) {
-		debug("%s: invlaid checksum-algorithm %s for %s\n",
-		      __func__, info->checksum->name, info->crypto->name);
-		return -EINVAL;
-	}
-
-	/* Calculate checksum with checksum-algorithm */
-	ret = info->checksum->calculate(info->checksum->name,
-					region, region_count, hash);
-	if (ret < 0) {
-		debug("%s: Error in checksum calculation\n", __func__);
-		return -EINVAL;
-	}
-
 	if (CONFIG_IS_ENABLED(RSA_VERIFY_WITH_PKEY) && !info->fdt_blob) {
 		/* don't rely on fdt properties */
 		ret = rsa_verify_with_pkey(info, hash, sig, sig_len);
@@ -555,3 +533,33 @@ int rsa_verify(struct image_sign_info *info,
 
 	return ret;
 }
+
+int rsa_verify(struct image_sign_info *info,
+	       const struct image_region region[], int region_count,
+	       uint8_t *sig, uint sig_len)
+{
+	/* Reserve memory for maximum checksum-length */
+	uint8_t hash[info->crypto->key_len];
+	int ret = -EACCES;
+
+	/*
+	 * Verify that the checksum-length does not exceed the
+	 * rsa-signature-length
+	 */
+	if (info->checksum->checksum_len >
+	    info->crypto->key_len) {
+		debug("%s: invlaid checksum-algorithm %s for %s\n",
+		      __func__, info->checksum->name, info->crypto->name);
+		return -EINVAL;
+	}
+
+	/* Calculate checksum with checksum-algorithm */
+	ret = info->checksum->calculate(info->checksum->name,
+					region, region_count, hash);
+	if (ret < 0) {
+		debug("%s: Error in checksum calculation\n", __func__);
+		return -EINVAL;
+	}
+
+	return rsa_verify_hash(info, hash, sig, sig_len);
+}
-- 
2.25.1