psa: Introduce PSA crypto core common symbols

When compiling some PSA core files of the
PSA cryptography repository, both the
Mbed TLS library and the PSA cryptography
core common.h are included and if they
define the same inline functions (same name),
the compilation fails.

Thus, inline functions prefixed by psa_crypto_
instead of mbedtls_ are defined in the
PSA cryptography core common.h header.

To ease the maintenance of the PSA cryptography
repository, introduce those symbols in Mbed TLS
as well and use them in PSA crypto core code
files instead of their Mbed TLS equivalent.

Signed-off-by: Ronald Cron <ronald.cron@arm.com>

library/psa_crypto.c

@@ -19,6 +19,7 @@
  */
 
 #include "common.h"
+#include "psa_crypto_core_common.h"
 
 #if defined(MBEDTLS_PSA_CRYPTO_C)
 
@@ -4226,7 +4227,7 @@ psa_status_t psa_cipher_encrypt(mbedtls_svc_key_id_t key,
     status = psa_driver_wrapper_cipher_encrypt(
         &attributes, slot->key.data, slot->key.bytes,
         alg, local_iv, default_iv_length, input, input_length,
-        mbedtls_buffer_offset(output, default_iv_length),
+        psa_crypto_buffer_offset(output, default_iv_length),
         output_size - default_iv_length, output_length);
 
 exit:

library/psa_crypto_core_common.h

@@ -0,0 +1,64 @@
+/**
+ * \file psa_crypto_core_common.h
+ *
+ * \brief Utility macros for internal use in the PSA cryptography core.
+ */
+/*
+ *  Copyright The Mbed TLS Contributors
+ *  SPDX-License-Identifier: Apache-2.0
+ *
+ *  Licensed under the Apache License, Version 2.0 (the "License"); you may
+ *  not use this file except in compliance with the License.
+ *  You may obtain a copy of the License at
+ *
+ *  http://www.apache.org/licenses/LICENSE-2.0
+ *
+ *  Unless required by applicable law or agreed to in writing, software
+ *  distributed under the License is distributed on an "AS IS" BASIS, WITHOUT
+ *  WARRANTIES OR CONDITIONS OF ANY KIND, either express or implied.
+ *  See the License for the specific language governing permissions and
+ *  limitations under the License.
+ */
+
+#ifndef PSA_CRYPTO_CORE_COMMON_H
+#define PSA_CRYPTO_CORE_COMMON_H
+
+/** Return an offset into a buffer.
+ *
+ * This is just the addition of an offset to a pointer, except that this
+ * function also accepts an offset of 0 into a buffer whose pointer is null.
+ * (`p + n` has undefined behavior when `p` is null, even when `n == 0`.
+ * A null pointer is a valid buffer pointer when the size is 0, for example
+ * as the result of `malloc(0)` on some platforms.)
+ *
+ * \param p     Pointer to a buffer of at least n bytes.
+ *              This may be \p NULL if \p n is zero.
+ * \param n     An offset in bytes.
+ * \return      Pointer to offset \p n in the buffer \p p.
+ *              Note that this is only a valid pointer if the size of the
+ *              buffer is at least \p n + 1.
+ */
+static inline unsigned char *psa_crypto_buffer_offset(
+    unsigned char *p, size_t n)
+{
+    return p == NULL ? NULL : p + n;
+}
+
+/** Return an offset into a read-only buffer.
+ *
+ * Similar to mbedtls_buffer_offset(), but for const pointers.
+ *
+ * \param p     Pointer to a buffer of at least n bytes.
+ *              This may be \p NULL if \p n is zero.
+ * \param n     An offset in bytes.
+ * \return      Pointer to offset \p n in the buffer \p p.
+ *              Note that this is only a valid pointer if the size of the
+ *              buffer is at least \p n + 1.
+ */
+static inline const unsigned char *psa_crypto_buffer_offset_const(
+    const unsigned char *p, size_t n)
+{
+    return p == NULL ? NULL : p + n;
+}
+
+#endif /* PSA_CRYPTO_CORE_COMMON_H */