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mbedtls/library/psa_crypto_se.c
Gilles Peskine 75c126b958 Explain some non-obvious parts of the code 
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2019-07-24 15:56:01 +02:00

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/*
* PSA crypto support for secure element drivers
*/
/* Copyright (C) 2019, ARM Limited, All Rights Reserved
* 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.
*
* This file is part of Mbed TLS (https://tls.mbed.org)
*/
#if !defined(MBEDTLS_CONFIG_FILE)
#include "mbedtls/config.h"
#else
#include MBEDTLS_CONFIG_FILE
#endif
#if defined(MBEDTLS_PSA_CRYPTO_SE_C)
#include <assert.h>
#include <stdint.h>
#include <string.h>
#include "psa/crypto_se_driver.h"
#include "psa_crypto_se.h"
#if defined(MBEDTLS_PSA_ITS_FILE_C)
#include "psa_crypto_its.h"
#else /* Native ITS implementation */
#include "psa/error.h"
#include "psa/internal_trusted_storage.h"
#endif
#include "mbedtls/platform.h"
#if !defined(MBEDTLS_PLATFORM_C)
#define mbedtls_calloc calloc
#define mbedtls_free free
#endif
/****************************************************************/
/* Driver lookup */
/****************************************************************/
/* This structure is identical to psa_drv_se_context_t declared in
* `crypto_se_driver.h`, except that some parts are writable here
* (non-const, or pointer to non-const). */
typedef struct
{
void *persistent_data;
size_t persistent_data_size;
uintptr_t transient_data;
} psa_drv_se_internal_context_t;
typedef struct psa_se_drv_table_entry_s
{
psa_key_lifetime_t lifetime;
const psa_drv_se_t *methods;
union
{
psa_drv_se_internal_context_t internal;
psa_drv_se_context_t context;
};
} psa_se_drv_table_entry_t;
static psa_se_drv_table_entry_t driver_table[PSA_MAX_SE_DRIVERS];
psa_se_drv_table_entry_t *psa_get_se_driver_entry(
psa_key_lifetime_t lifetime )
{
size_t i;
/* In the driver table, lifetime=0 means an entry that isn't used.
* No driver has a lifetime of 0 because it's a reserved value
* (which designates volatile keys). Make sure we never return
* a driver entry for lifetime 0. */
if( lifetime == 0 )
return( NULL );
for( i = 0; i < PSA_MAX_SE_DRIVERS; i++ )
{
if( driver_table[i].lifetime == lifetime )
return( &driver_table[i] );
}
return( NULL );
}
const psa_drv_se_t *psa_get_se_driver_methods(
const psa_se_drv_table_entry_t *driver )
{
return( driver->methods );
}
psa_drv_se_context_t *psa_get_se_driver_context(
psa_se_drv_table_entry_t *driver )
{
return( &driver->context );
}
int psa_get_se_driver( psa_key_lifetime_t lifetime,
const psa_drv_se_t **p_methods,
psa_drv_se_context_t **p_drv_context)
{
psa_se_drv_table_entry_t *driver = psa_get_se_driver_entry( lifetime );
if( p_methods != NULL )
*p_methods = ( driver ? driver->methods : NULL );
if( p_drv_context != NULL )
*p_drv_context = ( driver ? &driver->context : NULL );
return( driver != NULL );
}
/****************************************************************/
/* Persistent data management */
/****************************************************************/
static psa_status_t psa_get_se_driver_its_file_uid(
const psa_se_drv_table_entry_t *driver,
psa_storage_uid_t *uid )
{
if( driver->lifetime > PSA_MAX_SE_LIFETIME )
return( PSA_ERROR_NOT_SUPPORTED );
#if SIZE_MAX > UINT32_MAX
/* ITS file sizes are limited to 32 bits. */
if( driver->internal.persistent_data_size > UINT32_MAX )
return( PSA_ERROR_NOT_SUPPORTED );
#endif
/* See the documentation of PSA_CRYPTO_SE_DRIVER_ITS_UID_BASE. */
*uid = PSA_CRYPTO_SE_DRIVER_ITS_UID_BASE + driver->lifetime;
return( PSA_SUCCESS );
}
psa_status_t psa_load_se_persistent_data(
const psa_se_drv_table_entry_t *driver )
{
psa_status_t status;
psa_storage_uid_t uid;
status = psa_get_se_driver_its_file_uid( driver, &uid );
if( status != PSA_SUCCESS )
return( status );
/* psa_get_se_driver_its_file_uid ensures that the size_t
* persistent_data_size is in range, but compilers don't know that,
* so cast to reassure them. */
return( psa_its_get( uid, 0,
(uint32_t) driver->internal.persistent_data_size,
driver->internal.persistent_data ) );
}
psa_status_t psa_save_se_persistent_data(
const psa_se_drv_table_entry_t *driver )
{
psa_status_t status;
psa_storage_uid_t uid;
status = psa_get_se_driver_its_file_uid( driver, &uid );
if( status != PSA_SUCCESS )
return( status );
/* psa_get_se_driver_its_file_uid ensures that the size_t
* persistent_data_size is in range, but compilers don't know that,
* so cast to reassure them. */
return( psa_its_set( uid,
(uint32_t) driver->internal.persistent_data_size,
driver->internal.persistent_data,
0 ) );
}
psa_status_t psa_destroy_se_persistent_data( psa_key_lifetime_t lifetime )
{
psa_storage_uid_t uid;
if( lifetime > PSA_MAX_SE_LIFETIME )
return( PSA_ERROR_NOT_SUPPORTED );
uid = PSA_CRYPTO_SE_DRIVER_ITS_UID_BASE + lifetime;
return( psa_its_remove( uid ) );
}
psa_status_t psa_find_se_slot_for_key(
const psa_key_attributes_t *attributes,
psa_se_drv_table_entry_t *driver,
psa_key_slot_number_t *slot_number )
{
psa_status_t status;
psa_drv_se_allocate_key_t p_allocate = NULL;
/* If the lifetime is wrong, it's a bug in the library. */
if( driver->lifetime != attributes->lifetime )
return( PSA_ERROR_CORRUPTION_DETECTED );
/* If the driver doesn't support key creation in any way, give up now. */
if( driver->methods->key_management == NULL )
return( PSA_ERROR_NOT_SUPPORTED );
p_allocate = driver->methods->key_management->p_allocate;
/* If the driver doesn't tell us how to allocate a slot, that's
* not supported for the time being. */
if( p_allocate == NULL )
return( PSA_ERROR_NOT_SUPPORTED );
status = ( *p_allocate )( &driver->context,
driver->internal.persistent_data,
attributes,
slot_number );
return( status );
}
psa_status_t psa_destroy_se_key( psa_se_drv_table_entry_t *driver,
psa_key_slot_number_t slot_number )
{
psa_status_t status;
psa_status_t storage_status;
if( driver->methods->key_management == NULL ||
driver->methods->key_management->p_destroy == NULL )
return( PSA_ERROR_NOT_PERMITTED );
status = driver->methods->key_management->p_destroy(
&driver->context,
driver->internal.persistent_data,
slot_number );
storage_status = psa_save_se_persistent_data( driver );
return( status == PSA_SUCCESS ? storage_status : status );
}
/****************************************************************/
/* Driver registration */
/****************************************************************/
psa_status_t psa_register_se_driver(
psa_key_lifetime_t lifetime,
const psa_drv_se_t *methods)
{
size_t i;
psa_status_t status;
if( methods->hal_version != PSA_DRV_SE_HAL_VERSION )
return( PSA_ERROR_NOT_SUPPORTED );
/* Driver table entries are 0-initialized. 0 is not a valid driver
* lifetime because it means a volatile key. */
#if defined(static_assert)
static_assert( PSA_KEY_LIFETIME_VOLATILE == 0,
"Secure element support requires 0 to mean a volatile key" );
#endif
if( lifetime == PSA_KEY_LIFETIME_VOLATILE ||
lifetime == PSA_KEY_LIFETIME_PERSISTENT )
{
return( PSA_ERROR_INVALID_ARGUMENT );
}
if( lifetime > PSA_MAX_SE_LIFETIME )
return( PSA_ERROR_NOT_SUPPORTED );
for( i = 0; i < PSA_MAX_SE_DRIVERS; i++ )
{
if( driver_table[i].lifetime == 0 )
break;
/* Check that lifetime isn't already in use up to the first free
* entry. Since entries are created in order and never deleted,
* there can't be a used entry after the first free entry. */
if( driver_table[i].lifetime == lifetime )
return( PSA_ERROR_ALREADY_EXISTS );
}
if( i == PSA_MAX_SE_DRIVERS )
return( PSA_ERROR_INSUFFICIENT_MEMORY );
driver_table[i].lifetime = lifetime;
driver_table[i].methods = methods;
if( methods->persistent_data_size != 0 )
{
driver_table[i].internal.persistent_data =
mbedtls_calloc( 1, methods->persistent_data_size );
if( driver_table[i].internal.persistent_data == NULL )
{
status = PSA_ERROR_INSUFFICIENT_MEMORY;
goto error;
}
/* Load the driver's persistent data. On first use, the persistent
* data does not exist in storage, and is initialized to
* all-bits-zero by the calloc call just above. */
status = psa_load_se_persistent_data( &driver_table[i] );
if( status != PSA_SUCCESS && status != PSA_ERROR_DOES_NOT_EXIST )
goto error;
}
driver_table[i].internal.persistent_data_size =
methods->persistent_data_size;
return( PSA_SUCCESS );
error:
memset( &driver_table[i], 0, sizeof( driver_table[i] ) );
return( status );
}
void psa_unregister_all_se_drivers( void )
{
size_t i;
for( i = 0; i < PSA_MAX_SE_DRIVERS; i++ )
{
if( driver_table[i].internal.persistent_data != NULL )
mbedtls_free( driver_table[i].internal.persistent_data );
}
memset( driver_table, 0, sizeof( driver_table ) );
}
/****************************************************************/
/* The end */
/****************************************************************/
#endif /* MBEDTLS_PSA_CRYPTO_SE_C */
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