On the quest to remove all VLAs from the kernel[1], this avoids VLAs by just using the maximum allocation size (4 bytes) for stack arrays. All the VLAs in ecc were either 3 or 4 bytes (or a multiple), so just make it 4 bytes all the time. Initialization routines are adjusted to check that ndigits does not end up larger than the arrays.
[1] https://lkml.org/lkml/2018/3/7/621 Signed-off-by: Kees Cook <keesc...@chromium.org> --- This expects 14de52112ee70ca289fa77bf2d9cbc79fd2c811f to be reverted. --- crypto/ecc.c | 47 ++++++++++++++++++++++++----------------------- crypto/ecc.h | 4 +++- crypto/ecdh.c | 4 ++-- 3 files changed, 29 insertions(+), 26 deletions(-) diff --git a/crypto/ecc.c b/crypto/ecc.c index 18f32f2a5e1c..815541309a95 100644 --- a/crypto/ecc.c +++ b/crypto/ecc.c @@ -515,7 +515,7 @@ static void vli_mmod_fast_256(u64 *result, const u64 *product, static bool vli_mmod_fast(u64 *result, u64 *product, const u64 *curve_prime, unsigned int ndigits) { - u64 tmp[2 * ndigits]; + u64 tmp[2 * ECC_MAX_DIGITS]; switch (ndigits) { case 3: @@ -536,7 +536,7 @@ static bool vli_mmod_fast(u64 *result, u64 *product, static void vli_mod_mult_fast(u64 *result, const u64 *left, const u64 *right, const u64 *curve_prime, unsigned int ndigits) { - u64 product[2 * ndigits]; + u64 product[2 * ECC_MAX_DIGITS]; vli_mult(product, left, right, ndigits); vli_mmod_fast(result, product, curve_prime, ndigits); @@ -546,7 +546,7 @@ static void vli_mod_mult_fast(u64 *result, const u64 *left, const u64 *right, static void vli_mod_square_fast(u64 *result, const u64 *left, const u64 *curve_prime, unsigned int ndigits) { - u64 product[2 * ndigits]; + u64 product[2 * ECC_MAX_DIGITS]; vli_square(product, left, ndigits); vli_mmod_fast(result, product, curve_prime, ndigits); @@ -560,8 +560,8 @@ static void vli_mod_square_fast(u64 *result, const u64 *left, static void vli_mod_inv(u64 *result, const u64 *input, const u64 *mod, unsigned int ndigits) { - u64 a[ndigits], b[ndigits]; - u64 u[ndigits], v[ndigits]; + u64 a[ECC_MAX_DIGITS], b[ECC_MAX_DIGITS]; + u64 u[ECC_MAX_DIGITS], v[ECC_MAX_DIGITS]; u64 carry; int cmp_result; @@ -649,8 +649,8 @@ static void ecc_point_double_jacobian(u64 *x1, u64 *y1, u64 *z1, u64 *curve_prime, unsigned int ndigits) { /* t1 = x, t2 = y, t3 = z */ - u64 t4[ndigits]; - u64 t5[ndigits]; + u64 t4[ECC_MAX_DIGITS]; + u64 t5[ECC_MAX_DIGITS]; if (vli_is_zero(z1, ndigits)) return; @@ -711,7 +711,7 @@ static void ecc_point_double_jacobian(u64 *x1, u64 *y1, u64 *z1, static void apply_z(u64 *x1, u64 *y1, u64 *z, u64 *curve_prime, unsigned int ndigits) { - u64 t1[ndigits]; + u64 t1[ECC_MAX_DIGITS]; vli_mod_square_fast(t1, z, curve_prime, ndigits); /* z^2 */ vli_mod_mult_fast(x1, x1, t1, curve_prime, ndigits); /* x1 * z^2 */ @@ -724,7 +724,7 @@ static void xycz_initial_double(u64 *x1, u64 *y1, u64 *x2, u64 *y2, u64 *p_initial_z, u64 *curve_prime, unsigned int ndigits) { - u64 z[ndigits]; + u64 z[ECC_MAX_DIGITS]; vli_set(x2, x1, ndigits); vli_set(y2, y1, ndigits); @@ -750,7 +750,7 @@ static void xycz_add(u64 *x1, u64 *y1, u64 *x2, u64 *y2, u64 *curve_prime, unsigned int ndigits) { /* t1 = X1, t2 = Y1, t3 = X2, t4 = Y2 */ - u64 t5[ndigits]; + u64 t5[ECC_MAX_DIGITS]; /* t5 = x2 - x1 */ vli_mod_sub(t5, x2, x1, curve_prime, ndigits); @@ -791,9 +791,9 @@ static void xycz_add_c(u64 *x1, u64 *y1, u64 *x2, u64 *y2, u64 *curve_prime, unsigned int ndigits) { /* t1 = X1, t2 = Y1, t3 = X2, t4 = Y2 */ - u64 t5[ndigits]; - u64 t6[ndigits]; - u64 t7[ndigits]; + u64 t5[ECC_MAX_DIGITS]; + u64 t6[ECC_MAX_DIGITS]; + u64 t7[ECC_MAX_DIGITS]; /* t5 = x2 - x1 */ vli_mod_sub(t5, x2, x1, curve_prime, ndigits); @@ -846,9 +846,9 @@ static void ecc_point_mult(struct ecc_point *result, unsigned int ndigits) { /* R0 and R1 */ - u64 rx[2][ndigits]; - u64 ry[2][ndigits]; - u64 z[ndigits]; + u64 rx[2][ECC_MAX_DIGITS]; + u64 ry[2][ECC_MAX_DIGITS]; + u64 z[ECC_MAX_DIGITS]; int i, nb; int num_bits = vli_num_bits(scalar, ndigits); @@ -943,13 +943,13 @@ int ecc_is_key_valid(unsigned int curve_id, unsigned int ndigits, int ecc_gen_privkey(unsigned int curve_id, unsigned int ndigits, u64 *privkey) { const struct ecc_curve *curve = ecc_get_curve(curve_id); - u64 priv[ndigits]; + u64 priv[ECC_MAX_DIGITS]; unsigned int nbytes = ndigits << ECC_DIGITS_TO_BYTES_SHIFT; unsigned int nbits = vli_num_bits(curve->n, ndigits); int err; /* Check that N is included in Table 1 of FIPS 186-4, section 6.1.1 */ - if (nbits < 160) + if (nbits < 160 || ndigits > ARRAY_SIZE(priv)) return -EINVAL; /* @@ -988,10 +988,10 @@ int ecc_make_pub_key(unsigned int curve_id, unsigned int ndigits, { int ret = 0; struct ecc_point *pk; - u64 priv[ndigits]; + u64 priv[ECC_MAX_DIGITS]; const struct ecc_curve *curve = ecc_get_curve(curve_id); - if (!private_key || !curve) { + if (!private_key || !curve || ndigits > ARRAY_SIZE(priv)) { ret = -EINVAL; goto out; } @@ -1025,12 +1025,13 @@ int crypto_ecdh_shared_secret(unsigned int curve_id, unsigned int ndigits, { int ret = 0; struct ecc_point *product, *pk; - u64 priv[ndigits]; - u64 rand_z[ndigits]; + u64 priv[ECC_MAX_DIGITS]; + u64 rand_z[ECC_MAX_DIGITS]; unsigned int nbytes; const struct ecc_curve *curve = ecc_get_curve(curve_id); - if (!private_key || !public_key || !curve) { + if (!private_key || !public_key || !curve || + ndigits > ARRAY_SIZE(priv) || ndigits > ARRAY_SIZE(rand_z)) { ret = -EINVAL; goto out; } diff --git a/crypto/ecc.h b/crypto/ecc.h index e4fd4492c765..f75a86baa3bd 100644 --- a/crypto/ecc.h +++ b/crypto/ecc.h @@ -26,7 +26,9 @@ #ifndef _CRYPTO_ECC_H #define _CRYPTO_ECC_H -#define ECC_MAX_DIGITS 4 /* 256 */ +#define ECC_CURVE_NIST_P192_DIGITS 3 +#define ECC_CURVE_NIST_P256_DIGITS 4 +#define ECC_MAX_DIGITS ECC_CURVE_NIST_P256_DIGITS #define ECC_DIGITS_TO_BYTES_SHIFT 3 diff --git a/crypto/ecdh.c b/crypto/ecdh.c index 3aca0933ec44..3f91ef13c8c6 100644 --- a/crypto/ecdh.c +++ b/crypto/ecdh.c @@ -30,8 +30,8 @@ static inline struct ecdh_ctx *ecdh_get_ctx(struct crypto_kpp *tfm) static unsigned int ecdh_supported_curve(unsigned int curve_id) { switch (curve_id) { - case ECC_CURVE_NIST_P192: return 3; - case ECC_CURVE_NIST_P256: return 4; + case ECC_CURVE_NIST_P192: return ECC_CURVE_NIST_P192_DIGITS; + case ECC_CURVE_NIST_P256: return ECC_CURVE_NIST_P256_DIGITS; default: return 0; } } -- 2.7.4 -- Kees Cook Pixel Security
