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Simplify and explain the overflow check for maximum slice length

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Signed-off-by: Gilles Peskine <Gilles.Peskine@arm.com>
This commit is contained in:
Gilles Peskine 2024-08-21 21:46:26 +02:00
parent 0b2bd071f8
commit 4c9fccff5a
1 changed files with 12 additions and 5 deletions
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17
tf-psa-crypto/core/psa_crypto_slot_management.c
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@ -96,6 +96,18 @@ MBEDTLS_STATIC_ASSERT(PSA_KEY_ID_VOLATILE_MAX < MBEDTLS_PSA_KEY_ID_BUILTIN_MIN |
#define KEY_SLICE_COUNT (KEY_SLOT_VOLATILE_SLICE_COUNT + 1u)
#define KEY_SLOT_CACHE_SLICE_INDEX KEY_SLOT_VOLATILE_SLICE_COUNT
/* Check that the length of the largest slice (calculated as
* KEY_SLICE_LENGTH_MAX below) does not overflow size_t. We use
* an indirect method in case the calculation of KEY_SLICE_LENGTH_MAX
* itself overflows uintmax_t: if (BASE_LENGTH << c)
* overflows size_t then BASE_LENGTH > SIZE_MAX >> c.
*/
#if (KEY_SLOT_VOLATILE_SLICE_BASE_LENGTH > \
SIZE_MAX >> (KEY_SLOT_VOLATILE_SLICE_COUNT - 1))
#error "Maximum slice length overflows size_t"
#endif
#if KEY_ID_SLICE_INDEX_WIDTH + KEY_ID_SLOT_INDEX_WIDTH > 30
#error "Not enough room in volatile key IDs for slice index and slot index"
#endif
@ -111,11 +123,6 @@ MBEDTLS_STATIC_ASSERT(PSA_KEY_ID_VOLATILE_MAX < MBEDTLS_PSA_KEY_ID_BUILTIN_MIN |
#error "Slice index does not fit in uint8_t for psa_key_slot_t::slice_index"
#endif
MBEDTLS_STATIC_ASSERT((KEY_SLOT_VOLATILE_SLICE_BASE_LENGTH
& (SIZE_MAX >> (KEY_SLOT_VOLATILE_SLICE_COUNT - 1)))
== KEY_SLOT_VOLATILE_SLICE_BASE_LENGTH,
"Maximum slice length overflows size_t");
/* Calculate the volatile key id to use for a given slot.
* This function assumes valid parameter values. */