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Add tests for optionally safe codepaths

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The new test hooks allow to check whether there was an unsafe call of an
optionally safe function in the codepath. For the sake of simplicity the
MBEDTLS_MPI_IS_* macros are reused for signalling safe/unsafe codepaths
here too.

Signed-off-by: Janos Follath <janos.follath@arm.com>
This commit is contained in:
Janos Follath 2024-08-13 08:40:31 +01:00 committed by Manuel Pégourié-Gonnard
parent a099ac9812
commit df5e55bcb7
3 changed files with 40 additions and 0 deletions
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18
tf-psa-crypto/drivers/builtin/src/bignum_core.c
View File

@ -766,6 +766,9 @@ static inline void exp_mod_calc_first_bit_optionally_safe(const mbedtls_mpi_uint
*E_limb_index = E_bits / biL;
*E_bit_index = E_bits % biL;
}
#if defined(MBEDTLS_TEST_HOOKS)
mbedtls_mpi_optionally_safe_codepath = MBEDTLS_MPI_IS_PUBLIC;
#endif
} else {
/*
* Here we need to be constant time with respect to E and can't do anything better than
@ -773,6 +776,12 @@ static inline void exp_mod_calc_first_bit_optionally_safe(const mbedtls_mpi_uint
*/
*E_limb_index = E_limbs;
*E_bit_index = 0;
#if defined(MBEDTLS_TEST_HOOKS)
// Only mark the codepath safe if there wasn't an unsafe codepath before
if (mbedtls_mpi_optionally_safe_codepath != MBEDTLS_MPI_IS_PUBLIC) {
mbedtls_mpi_optionally_safe_codepath = MBEDTLS_MPI_IS_SECRET;
}
#endif
}
}
@ -789,11 +798,20 @@ static inline void exp_mod_table_lookup_optionally_safe(mbedtls_mpi_uint *Wselec
{
if (window_public == MBEDTLS_MPI_IS_PUBLIC) {
memcpy(Wselect, Wtable + window * AN_limbs, AN_limbs * ciL);
#if defined(MBEDTLS_TEST_HOOKS)
mbedtls_mpi_optionally_safe_codepath = MBEDTLS_MPI_IS_PUBLIC;
#endif
} else {
/* Select Wtable[window] without leaking window through
* memory access patterns. */
mbedtls_mpi_core_ct_uint_table_lookup(Wselect, Wtable,
AN_limbs, welem, window);
#if defined(MBEDTLS_TEST_HOOKS)
// Only mark the codepath safe if there wasn't an unsafe codepath before
if (mbedtls_mpi_optionally_safe_codepath != MBEDTLS_MPI_IS_PUBLIC) {
mbedtls_mpi_optionally_safe_codepath = MBEDTLS_MPI_IS_SECRET;
}
#endif
}
}

10
tf-psa-crypto/drivers/builtin/src/bignum_core.h
View File

@ -830,4 +830,14 @@ void mbedtls_mpi_core_from_mont_rep(mbedtls_mpi_uint *X,
mbedtls_mpi_uint mm,
mbedtls_mpi_uint *T);
#if defined(MBEDTLS_TEST_HOOKS)
int mbedtls_mpi_optionally_safe_codepath;
static inline void mbedtls_mpi_optionally_safe_codepath_reset()
{
// Set to a default that is neither MBEDTLS_MPI_IS_PUBLIC nor MBEDTLS_MPI_IS_SECRET
mbedtls_mpi_optionally_safe_codepath = MBEDTLS_MPI_IS_PUBLIC + MBEDTLS_MPI_IS_SECRET + 1;
}
#endif
#endif /* MBEDTLS_BIGNUM_CORE_H */

12
tf-psa-crypto/tests/suites/test_suite_bignum_core.function
View File

@ -1301,7 +1301,13 @@ void mpi_core_exp_mod(char *input_N, char *input_A,
TEST_CF_SECRET(N, N_limbs * sizeof(mbedtls_mpi_uint));
TEST_CF_SECRET(E, E_limbs * sizeof(mbedtls_mpi_uint));
#if defined(MBEDTLS_TEST_HOOKS)
mbedtls_mpi_optionally_safe_codepath_reset();
#endif
mbedtls_mpi_core_exp_mod(Y, A, N, N_limbs, E, E_limbs, R2, T);
#if defined(MBEDTLS_TEST_HOOKS)
TEST_EQUAL(mbedtls_mpi_optionally_safe_codepath, MBEDTLS_MPI_IS_SECRET);
#endif
TEST_CF_PUBLIC(Y, N_limbs * sizeof(mbedtls_mpi_uint));
@ -1312,7 +1318,13 @@ void mpi_core_exp_mod(char *input_N, char *input_A,
TEST_CF_SECRET(E, E_limbs * sizeof(mbedtls_mpi_uint));
/* Check when output aliased to input */
#if defined(MBEDTLS_TEST_HOOKS)
mbedtls_mpi_optionally_safe_codepath_reset();
#endif
mbedtls_mpi_core_exp_mod(A, A, N, N_limbs, E, E_limbs, R2, T);
#if defined(MBEDTLS_TEST_HOOKS)
TEST_EQUAL(mbedtls_mpi_optionally_safe_codepath, MBEDTLS_MPI_IS_SECRET);
#endif
TEST_CF_PUBLIC(A, A_limbs * sizeof(mbedtls_mpi_uint));
TEST_EQUAL(0, memcmp(X, A, N_limbs * sizeof(mbedtls_mpi_uint)));