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SE support: Use a transaction when registering a key

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When registering a key in a secure element, go through the transaction
mechanism. This makes the code simpler, at the expense of a few extra
storage operations. Given that registering a key is typically very
rare over the lifetime of a device, this is an acceptable loss.

Drivers must now have a p_validate_slot_number method, otherwise
registering a key is not possible. This reduces the risk that due to a
mistake during the integration of a device, an application might claim
a slot in a way that is not supported by the driver.
This commit is contained in:
Gilles Peskine
2019-10-01 14:18:35 +02:00
parent 37b5c831b4
commit 3efcebbc5e
4 changed files with 30 additions and 47 deletions
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42
library/psa_crypto.c
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@ -1579,7 +1579,7 @@ static psa_status_t psa_start_key_creation(
#if defined(MBEDTLS_PSA_CRYPTO_SE_C)
/* For a key in a secure element, we need to do three things
* when creating a key (but not when registering an existing key):
* when creating or registering a key:
* create the key file in internal storage, create the
* key inside the secure element, and update the driver's
* persistent data. Start a transaction that will encompass these
@ -1592,7 +1592,7 @@ static psa_status_t psa_start_key_creation(
* secure element driver updates its persistent state, but we do not yet
* save the driver's persistent state, so that if the power fails,
* we can roll back to a state where the key doesn't exist. */
if( *p_drv != NULL && method != PSA_KEY_CREATION_REGISTER )
if( *p_drv != NULL )
{
status = psa_find_se_slot_for_key( attributes, method, *p_drv,
&slot->data.se.slot_number );
@ -1609,6 +1609,12 @@ static psa_status_t psa_start_key_creation(
return( status );
}
}
if( *p_drv == NULL && method == PSA_KEY_CREATION_REGISTER )
{
/* Key registration only makes sense with a secure element. */
return( PSA_ERROR_INVALID_ARGUMENT );
}
#endif /* MBEDTLS_PSA_CRYPTO_SE_C */
return( status );
@ -1883,7 +1889,6 @@ psa_status_t mbedtls_psa_register_se_key(
psa_status_t status;
psa_key_slot_t *slot = NULL;
psa_se_drv_table_entry_t *driver = NULL;
const psa_drv_se_t *drv;
psa_key_handle_t handle = 0;
/* Leaving attributes unspecified is not currently supported.
@ -1900,37 +1905,6 @@ psa_status_t mbedtls_psa_register_se_key(
if( status != PSA_SUCCESS )
goto exit;
if( driver == NULL )
{
status = PSA_ERROR_INVALID_ARGUMENT;
goto exit;
}
drv = psa_get_se_driver_methods( driver );
if ( psa_get_key_slot_number( attributes,
&slot->data.se.slot_number ) != PSA_SUCCESS )
{
/* The application didn't specify a slot number. This doesn't
* make sense when registering a slot. */
status = PSA_ERROR_INVALID_ARGUMENT;
goto exit;
}
/* If the driver has a slot number validation method, call it.
* If it doesn't, it means the secure element is unable to validate
* anything and so we have to trust the application. */
if( drv->key_management != NULL &&
drv->key_management->p_validate_slot_number != NULL )
{
status = drv->key_management->p_validate_slot_number(
psa_get_se_driver_context( driver ),
attributes,
PSA_KEY_CREATION_REGISTER,
slot->data.se.slot_number );
if( status != PSA_SUCCESS )
goto exit;
}
status = psa_finish_key_creation( slot, driver );
exit: