[PATCH v2] crypto: rsa-pkcs1pad: export rsa1_asn_lookup()

[Jarkko Sakkinen]

ASN.1 template is required for TPM2 asymmetric keys, as it needs to be
piggy-packed with the input data before applying TPM2_RSA_Decrypt. This
patch prepares crypto subsystem for the addition of those keys.

Later rsa_lookup_asn1() can be enabled in crypto/asymmetric_keys/Kconfig
by:

        depends on CRYPTO_RSA >= <TPM2 asymmetric keys>

Cc: James Prestwood <prest...@gmail.com>
Signed-off-by: Jarkko Sakkinen <jar...@kernel.org>
---
v2:
- Fix typo in the kdoc.
- Export also the template struct.
---
 crypto/rsa-pkcs1pad.c         | 16 ++++++++++------
 include/crypto/rsa-pkcs1pad.h | 20 ++++++++++++++++++++
 2 files changed, 30 insertions(+), 6 deletions(-)
 create mode 100644 include/crypto/rsa-pkcs1pad.h

diff --git a/crypto/rsa-pkcs1pad.c b/crypto/rsa-pkcs1pad.c
index cd501195f34a..ea162ccf28ec 100644
--- a/crypto/rsa-pkcs1pad.c
+++ b/crypto/rsa-pkcs1pad.c
@@ -7,6 +7,7 @@
 
 #include <crypto/algapi.h>
 #include <crypto/akcipher.h>
+#include <crypto/rsa-pkcs1pad.h>
 #include <crypto/internal/akcipher.h>
 #include <crypto/internal/rsa.h>
 #include <linux/err.h>
@@ -79,11 +80,7 @@ static const u8 rsa_digest_info_sha3_512[] = {
        0x05, 0x00, 0x04, 0x40
 };
 
-static const struct rsa_asn1_template {
-       const char      *name;
-       const u8        *data;
-       size_t          size;
-} rsa_asn1_templates[] = {
+const struct rsa_asn1_template rsa_asn1_templates[] = {
 #define _(X) { #X, rsa_digest_info_##X, sizeof(rsa_digest_info_##X) }
        _(md5),
        _(sha1),
@@ -101,7 +98,13 @@ static const struct rsa_asn1_template {
        { NULL }
 };
 
-static const struct rsa_asn1_template *rsa_lookup_asn1(const char *name)
+/**
+ * rsa_lookup_asn1() - Lookup the ASN.1 digest info given the hash
+ * name:       hash algorithm name
+ *
+ * Returns the ASN.1 digest info on success, and NULL on failure.
+ */
+const struct rsa_asn1_template *rsa_lookup_asn1(const char *name)
 {
        const struct rsa_asn1_template *p;
 
@@ -110,6 +113,7 @@ static const struct rsa_asn1_template 
*rsa_lookup_asn1(const char *name)
                        return p;
        return NULL;
 }
+EXPORT_SYMBOL_GPL(rsa_lookup_asn1);
 
 struct pkcs1pad_ctx {
        struct crypto_akcipher *child;
diff --git a/include/crypto/rsa-pkcs1pad.h b/include/crypto/rsa-pkcs1pad.h
new file mode 100644
index 000000000000..32c7453ff644
--- /dev/null
+++ b/include/crypto/rsa-pkcs1pad.h
@@ -0,0 +1,20 @@
+/* SPDX-License-Identifier: GPL-2.0 */
+/*
+ * RSA padding templates.
+ */
+
+#ifndef _CRYPTO_RSA_PKCS1PAD_H
+#define _CRYPTO_RSA_PKCS1PAD_H
+
+/*
+ * Hash algorithm name to ASN.1 template mapping.
+ */
+struct rsa_asn1_template {
+       const char *name;
+       const u8 *data;
+       size_t size;
+};
+
+const struct rsa_asn1_template *rsa_lookup_asn1(const char *name);
+
+#endif /* _CRYPTO_RSA_PKCS1PAD_H */
-- 
2.45.0