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psa: allow to use static key buffers instead of dynamic ones

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This helps reducing heap memory usage and, if heap memory is
not used anywhere else in an embedded device, it also reduces
code footprint since there is no need for heap management code
in this case.

A new build symbol is added for this purpose, named
MBEDTLS_PSA_STATIC_KEY_SLOTS. It's disabled by default so that
normal usage of Mbed TLS library is not affected.

Signed-off-by: Valerio Setti <valerio.setti@nordicsemi.no>
This commit is contained in:
Valerio Setti 2024-06-14 07:49:05 +02:00
parent 6b644938d2
commit 678e0fb3e5
6 changed files with 102 additions and 6 deletions
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33
include/mbedtls/mbedtls_config.h
View File

@ -3066,6 +3066,39 @@
*/
#define MBEDTLS_PSA_ITS_FILE_C
/**
* \def MBEDTLS_PSA_STATIC_KEY_SLOTS
*
* Statically preallocate all key slot buffers to store volatile keys in PSA
* instead of allocating them dynamically when required. This helps reducing
* heap memory usage as well as heap management code's footprint in embedded
* devices.
*
* \note This feature comes with a (potentially) higher RAM usage since:
* - All the key slots are allocated no matter if they are used of not.
* - Each key slot's length is as large as the largest key type supported
* in the build.
*
* Requires: MBEDTLS_PSA_CRYPTO_C
*
*/
//#define MBEDTLS_PSA_STATIC_KEY_SLOTS
/**
* \def MBEDTLS_PSA_STATIC_KEY_SLOTS
*
* Optionally define the size (in bytes) of each static key slot. If not
* explicitly defined then it's automatically set to hold the maximum
* asymmetric PSA key enabled in the build (through PSA_WANT_xxx symbols).
* If required by the application this parameter can be set to higher values
* in order to store larger objects (ex: raw keys), but please note that this
* will increase RAM usage.
*
* Requires: MBEDTLS_PSA_STATIC_KEY_SLOTS
*
*/
//#define MBEDTLS_PSA_STATIC_KEY_SLOT_BUFFER_SIZE 256
/**
* \def MBEDTLS_RIPEMD160_C
*

2
scripts/config.py
View File

@ -110,6 +110,8 @@ EXCLUDE_FROM_FULL = frozenset([
'MBEDTLS_TEST_CONSTANT_FLOW_MEMSAN', # build dependency (clang+memsan)
'MBEDTLS_TEST_CONSTANT_FLOW_VALGRIND', # build dependency (valgrind headers)
'MBEDTLS_X509_REMOVE_INFO', # removes a feature
'MBEDTLS_PSA_STATIC_KEY_SLOTS', # only relevant for embedded devices
'MBEDTLS_PSA_STATIC_KEY_SLOT_BUFFER_SIZE', # only relevant for embedded devices
*PSA_UNSUPPORTED_FEATURE,
*PSA_DEPRECATED_FEATURE,
*PSA_UNSTABLE_FEATURE

33
tf-psa-crypto/core/psa_crypto.c
View File

@ -705,6 +705,17 @@ MBEDTLS_STATIC_TESTABLE psa_status_t psa_mac_key_can_do(
psa_status_t psa_allocate_buffer_to_slot(psa_key_slot_t *slot,
size_t buffer_length)
{
#if defined(MBEDTLS_PSA_STATIC_KEY_SLOTS)
if (slot->key.in_use) {
return PSA_ERROR_ALREADY_EXISTS;
}
if (buffer_length > ((size_t) MBEDTLS_PSA_STATIC_KEY_SLOT_BUFFER_SIZE)) {
return PSA_ERROR_NOT_SUPPORTED;
}
slot->key.in_use = 1;
#else
if (slot->key.data != NULL) {
return PSA_ERROR_ALREADY_EXISTS;
}
@ -713,6 +724,7 @@ psa_status_t psa_allocate_buffer_to_slot(psa_key_slot_t *slot,
if (slot->key.data == NULL) {
return PSA_ERROR_INSUFFICIENT_MEMORY;
}
#endif
slot->key.bytes = buffer_length;
return PSA_SUCCESS;
@ -1177,11 +1189,16 @@ static psa_status_t psa_get_and_lock_transparent_key_slot_with_policy(
psa_status_t psa_remove_key_data_from_memory(psa_key_slot_t *slot)
{
#if defined(MBEDTLS_PSA_STATIC_KEY_SLOTS)
slot->key.in_use = 0;
#else /* MBEDTLS_PSA_STATIC_KEY_SLOTS */
if (slot->key.data != NULL) {
mbedtls_zeroize_and_free(slot->key.data, slot->key.bytes);
}
slot->key.data = NULL;
#endif /* MBEDTLS_PSA_STATIC_KEY_SLOTS */
slot->key.bytes = 0;
return PSA_SUCCESS;
@ -2096,7 +2113,13 @@ psa_status_t psa_import_key(const psa_key_attributes_t *attributes,
* storage ( thus not in the case of importing a key in a secure element
* with storage ( MBEDTLS_PSA_CRYPTO_SE_C ) ),we have to allocate a
* buffer to hold the imported key material. */
if (slot->key.data == NULL) {
#if defined(MBEDTLS_PSA_STATIC_KEY_SLOTS)
int is_slot_unused = (slot->key.in_use == 0);
#else
int is_slot_unused = (slot->key.data == NULL);
#endif
if (is_slot_unused) {
if (psa_key_lifetime_is_external(attributes->lifetime)) {
status = psa_driver_wrapper_get_key_buffer_size_from_key_data(
attributes, data, data_length, &storage_size);
@ -8030,7 +8053,13 @@ psa_status_t psa_generate_key_custom(const psa_key_attributes_t *attributes,
* storage ( thus not in the case of generating a key in a secure element
* with storage ( MBEDTLS_PSA_CRYPTO_SE_C ) ),we have to allocate a
* buffer to hold the generated key material. */
if (slot->key.data == NULL) {
#if defined(MBEDTLS_PSA_STATIC_KEY_SLOTS)
int is_slot_unused = (slot->key.in_use == 0);
#else
int is_slot_unused = (slot->key.data == NULL);
#endif
if (is_slot_unused) {
if (PSA_KEY_LIFETIME_GET_LOCATION(attributes->lifetime) ==
PSA_KEY_LOCATION_LOCAL_STORAGE) {
status = psa_validate_key_type_and_size_for_key_generation(

11
tf-psa-crypto/core/psa_crypto_core.h
View File

@ -55,6 +55,12 @@ typedef enum {
PSA_SLOT_PENDING_DELETION,
} psa_key_slot_state_t;
/* If the size of static key slots is not explicitly defined by the user, then
* set it to PSA_EXPORT_KEY_PAIR_OR_PUBLIC_MAX_SIZE. */
#if !defined(MBEDTLS_PSA_STATIC_KEY_SLOT_BUFFER_SIZE)
#define MBEDTLS_PSA_STATIC_KEY_SLOT_BUFFER_SIZE (PSA_EXPORT_KEY_PAIR_OR_PUBLIC_MAX_SIZE)
#endif /* !MBEDTLS_PSA_STATIC_KEY_SLOT_BUFFER_SIZE*/
/** The data structure representing a key slot, containing key material
* and metadata for one key.
*/
@ -155,7 +161,12 @@ typedef struct {
/* Dynamically allocated key data buffer.
* Format as specified in psa_export_key(). */
struct key_data {
#if defined(MBEDTLS_PSA_STATIC_KEY_SLOTS)
int in_use;
uint8_t data[MBEDTLS_PSA_STATIC_KEY_SLOT_BUFFER_SIZE];
#else /* MBEDTLS_PSA_STATIC_KEY_SLOTS */
uint8_t *data;
#endif /* MBEDTLS_PSA_STATIC_KEY_SLOTS */
size_t bytes;
} key;
} psa_key_slot_t;

4
tf-psa-crypto/drivers/builtin/src/pk.c
View File

@ -35,10 +35,6 @@
#include <limits.h>
#include <stdint.h>
#define PSA_EXPORT_KEY_PAIR_OR_PUBLIC_MAX_SIZE \
(PSA_EXPORT_KEY_PAIR_MAX_SIZE > PSA_EXPORT_PUBLIC_KEY_MAX_SIZE) ? \
PSA_EXPORT_KEY_PAIR_MAX_SIZE : PSA_EXPORT_PUBLIC_KEY_MAX_SIZE
/*
* Initialise a mbedtls_pk_context
*/

25
tf-psa-crypto/include/psa/crypto_sizes.h
View File

@ -1038,6 +1038,10 @@
PSA_KEY_EXPORT_FFDH_PUBLIC_KEY_MAX_SIZE(PSA_VENDOR_FFDH_MAX_KEY_BITS)
#endif
#define PSA_EXPORT_KEY_PAIR_OR_PUBLIC_MAX_SIZE \
(PSA_EXPORT_KEY_PAIR_MAX_SIZE > PSA_EXPORT_PUBLIC_KEY_MAX_SIZE) ? \
PSA_EXPORT_KEY_PAIR_MAX_SIZE : PSA_EXPORT_PUBLIC_KEY_MAX_SIZE
/** Sufficient output buffer size for psa_raw_key_agreement().
*
* This macro returns a compile-time constant if its arguments are
@ -1085,6 +1089,27 @@
#define PSA_RAW_KEY_AGREEMENT_OUTPUT_MAX_SIZE PSA_BITS_TO_BYTES(PSA_VENDOR_FFDH_MAX_KEY_BITS)
#endif
/** Maximum key length for ciphers.
*
* Since there is no additional PSA_WANT_xxx symbol to specifiy the size of
* the key once a cipher is enabled (as it happens for asymmetric keys for
* example), the maximum key length is taken into account for each cipher.
* The resulting value will be the maximum cipher's key length given depending
* on which ciphers are enabled.
*
* Note: max value for AES used below would be doubled if XTS were enabled, but
* this mode is currently not supported in Mbed TLS implementation of PSA
* APIs.
*/
#if (defined(PSA_WANT_KEY_TYPE_AES) || defined(PSA_WANT_KEY_TYPE_ARIA) || \
defined(PSA_WANT_KEY_TYPE_CAMELLIA) || defined(PSA_WANT_KEY_TYPE_CHACHA20))
#define PSA_CIPHER_MAX_KEY_LENGTH 32u
#elif defined(PSA_WANT_KEY_TYPE_DES)
#define PSA_CIPHER_MAX_KEY_LENGTH 24u
#else
#define PSA_CIPHER_MAX_KEY_LENGTH 0u
#endif
/** The default IV size for a cipher algorithm, in bytes.
*
* The IV that is generated as part of a call to #psa_cipher_encrypt() is always