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Date: Mon, 16 Apr 2018 09:04:56 -0700
From: Kees Cook <keescook@...omium.org>
To: Herbert Xu <herbert@...dor.apana.org.au>
Cc: linux-crypto <linux-crypto@...r.kernel.org>,
LKML <linux-kernel@...r.kernel.org>
Subject: Re: [PATCH v2] crypto/ecc: Actually remove stack VLA usage
On Fri, Mar 30, 2018 at 9:55 AM, Kees Cook <keescook@...omium.org> wrote:
> 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.
>
> This includes a removal of the earlier attempt at this fix from
> commit a963834b4742 ("crypto/ecc: Remove stack VLA usage")
>
> [1] https://lkml.org/lkml/2018/3/7/621
>
> Signed-off-by: Kees Cook <keescook@...omium.org>
Friendly ping. Please apply to fix a963834b4742 ("crypto/ecc: Remove
stack VLA usage").
Thanks!
-Kees
> ---
> v2:
> - Squash revert (herbert)
> ---
> crypto/ecc.c | 66 +++++++++++++++++++++++++----------------------------------
> crypto/ecc.h | 4 +++-
> crypto/ecdh.c | 4 ++--
> 3 files changed, 33 insertions(+), 41 deletions(-)
>
> diff --git a/crypto/ecc.c b/crypto/ecc.c
> index 9c066b5ac12d..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;
> }
> @@ -1025,30 +1025,25 @@ int crypto_ecdh_shared_secret(unsigned int curve_id, unsigned int ndigits,
> {
> int ret = 0;
> struct ecc_point *product, *pk;
> - u64 *priv, *rand_z;
> + 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;
> }
>
> - priv = kmalloc_array(ndigits, sizeof(*priv), GFP_KERNEL);
> - if (!priv) {
> - ret = -ENOMEM;
> - goto out;
> - }
> + nbytes = ndigits << ECC_DIGITS_TO_BYTES_SHIFT;
>
> - rand_z = kmalloc_array(ndigits, sizeof(*rand_z), GFP_KERNEL);
> - if (!rand_z) {
> - ret = -ENOMEM;
> - goto kfree_out;
> - }
> + get_random_bytes(rand_z, nbytes);
>
> pk = ecc_alloc_point(ndigits);
> if (!pk) {
> ret = -ENOMEM;
> - goto kfree_out;
> + goto out;
> }
>
> product = ecc_alloc_point(ndigits);
> @@ -1057,8 +1052,6 @@ int crypto_ecdh_shared_secret(unsigned int curve_id, unsigned int ndigits,
> goto err_alloc_product;
> }
>
> - get_random_bytes(rand_z, ndigits << ECC_DIGITS_TO_BYTES_SHIFT);
> -
> ecc_swap_digits(public_key, pk->x, ndigits);
> ecc_swap_digits(&public_key[ndigits], pk->y, ndigits);
> ecc_swap_digits(private_key, priv, ndigits);
> @@ -1073,9 +1066,6 @@ int crypto_ecdh_shared_secret(unsigned int curve_id, unsigned int ndigits,
> ecc_free_point(product);
> err_alloc_product:
> ecc_free_point(pk);
> -kfree_out:
> - kzfree(priv);
> - kzfree(rand_z);
> out:
> return ret;
> }
> 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
--
Kees Cook
Pixel Security
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