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Make integer downsizing explicit

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Reassure both humans and compilers that the places where we assign an
integer to a smaller type are safe.

Signed-off-by: Gilles Peskine <Gilles.Peskine@arm.com>
This commit is contained in:
Gilles Peskine 2024-06-13 20:36:50 +02:00
parent 75fd2401e5
commit 5abeb8c77b
1 changed files with 10 additions and 3 deletions
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13
tf-psa-crypto/core/psa_crypto_slot_management.c
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@ -116,7 +116,12 @@ MBEDTLS_STATIC_ASSERT(PSA_KEY_ID_VOLATILE_MAX < MBEDTLS_PSA_KEY_ID_BUILTIN_MIN |
static psa_key_id_t volatile_key_id_of_index(size_t slice_idx,
size_t slot_idx)
{
return 0x40000000u | (slice_idx << KEY_ID_SLOT_INDEX_WIDTH) | slot_idx;
/* We assert above that the slice and slot indexes fit in separate
* bit-fields inside psa_key_id_t, which is a 32-bit type per the
* PSA Cryptography specification. */
return (psa_key_id_t) (0x40000000u |
(slice_idx << KEY_ID_SLOT_INDEX_WIDTH) |
slot_idx);
}
/* Calculate the slice containing the given volatile key.
@ -529,7 +534,8 @@ static psa_status_t psa_allocate_volatile_key_slot(psa_key_id_t *key_id,
}
*p_slot = slot;
slot->slice_index = slice_idx;
/* We assert at compile time that the slice index fits in uint8_t. */
slot->slice_index = (uint8_t) slice_idx;
return PSA_SUCCESS;
}
@ -566,7 +572,8 @@ psa_status_t psa_free_key_slot(size_t slice_idx,
next_free = key_slice_length(slice_idx);
}
global_data.first_free_slot_index[slice_idx] = slot_idx;
slot->var.free.next_free_relative_to_next = next_free - slot_idx - 1;
slot->var.free.next_free_relative_to_next =
(int32_t) next_free - (int32_t) slot_idx - 1;
return PSA_SUCCESS;
}