Merge pull request #7859 from gilles-peskine-arm/mbedtls_mpi-smaller
Reduce the size of mbedtls_mpi
diff --git a/include/mbedtls/bignum.h b/include/mbedtls/bignum.h
index e7f3131..eb372cf 100644
--- a/include/mbedtls/bignum.h
+++ b/include/mbedtls/bignum.h
@@ -203,6 +203,12 @@
* \brief MPI structure
*/
typedef struct mbedtls_mpi {
+ /** Pointer to limbs.
+ *
+ * This may be \c NULL if \c n is 0.
+ */
+ mbedtls_mpi_uint *MBEDTLS_PRIVATE(p);
+
/** Sign: -1 if the mpi is negative, 1 otherwise.
*
* The number 0 must be represented with `s = +1`. Although many library
@@ -214,16 +220,19 @@
* Note that this implies that calloc() or `... = {0}` does not create
* a valid MPI representation. You must call mbedtls_mpi_init().
*/
- int MBEDTLS_PRIVATE(s);
+ signed short MBEDTLS_PRIVATE(s);
/** Total number of limbs in \c p. */
- size_t MBEDTLS_PRIVATE(n);
-
- /** Pointer to limbs.
- *
- * This may be \c NULL if \c n is 0.
+ unsigned short MBEDTLS_PRIVATE(n);
+ /* Make sure that MBEDTLS_MPI_MAX_LIMBS fits in n.
+ * Use the same limit value on all platforms so that we don't have to
+ * think about different behavior on the rare platforms where
+ * unsigned short can store values larger than the minimum required by
+ * the C language, which is 65535.
*/
- mbedtls_mpi_uint *MBEDTLS_PRIVATE(p);
+#if MBEDTLS_MPI_MAX_LIMBS > 65535
+#error "MBEDTLS_MPI_MAX_LIMBS > 65535 is not supported"
+#endif
}
mbedtls_mpi;
diff --git a/library/bignum.c b/library/bignum.c
index 36effaf..5b92932 100644
--- a/library/bignum.c
+++ b/library/bignum.c
@@ -114,7 +114,9 @@
mbedtls_free(X->p);
}
- X->n = nblimbs;
+ /* nblimbs fits in n because we ensure that MBEDTLS_MPI_MAX_LIMBS
+ * fits, and we've checked that nblimbs <= MBEDTLS_MPI_MAX_LIMBS. */
+ X->n = (unsigned short) nblimbs;
X->p = p;
}
@@ -162,7 +164,9 @@
mbedtls_free(X->p);
}
- X->n = i;
+ /* i fits in n because we ensure that MBEDTLS_MPI_MAX_LIMBS
+ * fits, and we've checked that i <= nblimbs <= MBEDTLS_MPI_MAX_LIMBS. */
+ X->n = (unsigned short) i;
X->p = p;
return 0;
@@ -1574,8 +1578,8 @@
{
mbedtls_mpi_uint z = 1;
mbedtls_mpi U;
-
- U.n = U.s = (int) z;
+ U.n = 1;
+ U.s = 1;
U.p = &z;
mpi_montmul(A, &U, N, mm, T);
diff --git a/library/ecp.c b/library/ecp.c
index b13cac0..049a1e0 100644
--- a/library/ecp.c
+++ b/library/ecp.c
@@ -2932,9 +2932,9 @@
#if defined(MBEDTLS_ECP_MONTGOMERY_ENABLED)
#if defined(MBEDTLS_ECP_DP_CURVE25519_ENABLED)
-#define ECP_MPI_INIT(s, n, p) { s, (n), (mbedtls_mpi_uint *) (p) }
+#define ECP_MPI_INIT(_p, _n) { .p = (mbedtls_mpi_uint *) (_p), .s = 1, .n = (_n) }
#define ECP_MPI_INIT_ARRAY(x) \
- ECP_MPI_INIT(1, sizeof(x) / sizeof(mbedtls_mpi_uint), x)
+ ECP_MPI_INIT(x, sizeof(x) / sizeof(mbedtls_mpi_uint))
/*
* Constants for the two points other than 0, 1, -1 (mod p) in
* https://cr.yp.to/ecdh.html#validate
diff --git a/library/ecp_curves.c b/library/ecp_curves.c
index a4fa663..3d3ec60 100644
--- a/library/ecp_curves.c
+++ b/library/ecp_curves.c
@@ -44,15 +44,15 @@
#define ECP_VALIDATE(cond) \
MBEDTLS_INTERNAL_VALIDATE(cond)
-#define ECP_MPI_INIT(s, n, p) { s, (n), (mbedtls_mpi_uint *) (p) }
+#define ECP_MPI_INIT(_p, _n) { .p = (mbedtls_mpi_uint *) (_p), .s = 1, .n = (_n) }
#define ECP_MPI_INIT_ARRAY(x) \
- ECP_MPI_INIT(1, sizeof(x) / sizeof(mbedtls_mpi_uint), x)
+ ECP_MPI_INIT(x, sizeof(x) / sizeof(mbedtls_mpi_uint))
#define ECP_POINT_INIT_XY_Z0(x, y) { \
- ECP_MPI_INIT_ARRAY(x), ECP_MPI_INIT_ARRAY(y), ECP_MPI_INIT(1, 0, NULL) }
+ ECP_MPI_INIT_ARRAY(x), ECP_MPI_INIT_ARRAY(y), ECP_MPI_INIT(NULL, 0) }
#define ECP_POINT_INIT_XY_Z1(x, y) { \
- ECP_MPI_INIT_ARRAY(x), ECP_MPI_INIT_ARRAY(y), ECP_MPI_INIT(1, 1, mpi_one) }
+ ECP_MPI_INIT_ARRAY(x), ECP_MPI_INIT_ARRAY(y), ECP_MPI_INIT(mpi_one, 1) }
#if defined(MBEDTLS_ECP_DP_SECP192R1_ENABLED) || \
defined(MBEDTLS_ECP_DP_SECP224R1_ENABLED) || \
@@ -4512,12 +4512,13 @@
defined(MBEDTLS_ECP_DP_CURVE448_ENABLED)
/*
* Create an MPI from embedded constants
- * (assumes len is an exact multiple of sizeof(mbedtls_mpi_uint))
+ * (assumes len is an exact multiple of sizeof(mbedtls_mpi_uint) and
+ * len < 1048576)
*/
static inline void ecp_mpi_load(mbedtls_mpi *X, const mbedtls_mpi_uint *p, size_t len)
{
X->s = 1;
- X->n = len / sizeof(mbedtls_mpi_uint);
+ X->n = (unsigned short) (len / sizeof(mbedtls_mpi_uint));
X->p = (mbedtls_mpi_uint *) p;
}
#endif
diff --git a/tests/suites/test_suite_bignum_random.function b/tests/suites/test_suite_bignum_random.function
index e4db3d7..34221a7 100644
--- a/tests/suites/test_suite_bignum_random.function
+++ b/tests/suites/test_suite_bignum_random.function
@@ -312,8 +312,8 @@
/* Temporarily use a legacy MPI for analysis, because the
* necessary auxiliary functions don't exist yet in core. */
- mbedtls_mpi B = { 1, limbs, upper_bound };
- mbedtls_mpi R = { 1, limbs, result };
+ mbedtls_mpi B = { .s = 1, .n = limbs, .p = upper_bound };
+ mbedtls_mpi R = { .s = 1, .n = limbs, .p = result };
TEST_ASSERT(mbedtls_mpi_cmp_mpi(&R, &B) < 0);
TEST_ASSERT(mbedtls_mpi_cmp_int(&R, min) >= 0);