linux/crypto/ecdh.c
Ard Biesheuvel 17858b140b crypto: ecdh - avoid unaligned accesses in ecdh_set_secret()
ecdh_set_secret() casts a void* pointer to a const u64* in order to
feed it into ecc_is_key_valid(). This is not generally permitted by
the C standard, and leads to actual misalignment faults on ARMv6
cores. In some cases, these are fixed up in software, but this still
leads to performance hits that are entirely avoidable.

So let's copy the key into the ctx buffer first, which we will do
anyway in the common case, and which guarantees correct alignment.

Cc: <stable@vger.kernel.org>
Signed-off-by: Ard Biesheuvel <ardb@kernel.org>
Signed-off-by: Herbert Xu <herbert@gondor.apana.org.au>
2020-12-04 18:13:13 +11:00

171 lines
4.0 KiB
C

// SPDX-License-Identifier: GPL-2.0-or-later
/* ECDH key-agreement protocol
*
* Copyright (c) 2016, Intel Corporation
* Authors: Salvator Benedetto <salvatore.benedetto@intel.com>
*/
#include <linux/module.h>
#include <crypto/internal/kpp.h>
#include <crypto/kpp.h>
#include <crypto/ecdh.h>
#include <linux/scatterlist.h>
#include "ecc.h"
struct ecdh_ctx {
unsigned int curve_id;
unsigned int ndigits;
u64 private_key[ECC_MAX_DIGITS];
};
static inline struct ecdh_ctx *ecdh_get_ctx(struct crypto_kpp *tfm)
{
return kpp_tfm_ctx(tfm);
}
static unsigned int ecdh_supported_curve(unsigned int curve_id)
{
switch (curve_id) {
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;
}
}
static int ecdh_set_secret(struct crypto_kpp *tfm, const void *buf,
unsigned int len)
{
struct ecdh_ctx *ctx = ecdh_get_ctx(tfm);
struct ecdh params;
unsigned int ndigits;
if (crypto_ecdh_decode_key(buf, len, &params) < 0)
return -EINVAL;
ndigits = ecdh_supported_curve(params.curve_id);
if (!ndigits)
return -EINVAL;
ctx->curve_id = params.curve_id;
ctx->ndigits = ndigits;
if (!params.key || !params.key_size)
return ecc_gen_privkey(ctx->curve_id, ctx->ndigits,
ctx->private_key);
memcpy(ctx->private_key, params.key, params.key_size);
if (ecc_is_key_valid(ctx->curve_id, ctx->ndigits,
ctx->private_key, params.key_size) < 0) {
memzero_explicit(ctx->private_key, params.key_size);
return -EINVAL;
}
return 0;
}
static int ecdh_compute_value(struct kpp_request *req)
{
struct crypto_kpp *tfm = crypto_kpp_reqtfm(req);
struct ecdh_ctx *ctx = ecdh_get_ctx(tfm);
u64 *public_key;
u64 *shared_secret = NULL;
void *buf;
size_t copied, nbytes, public_key_sz;
int ret = -ENOMEM;
nbytes = ctx->ndigits << ECC_DIGITS_TO_BYTES_SHIFT;
/* Public part is a point thus it has both coordinates */
public_key_sz = 2 * nbytes;
public_key = kmalloc(public_key_sz, GFP_KERNEL);
if (!public_key)
return -ENOMEM;
if (req->src) {
shared_secret = kmalloc(nbytes, GFP_KERNEL);
if (!shared_secret)
goto free_pubkey;
/* from here on it's invalid parameters */
ret = -EINVAL;
/* must have exactly two points to be on the curve */
if (public_key_sz != req->src_len)
goto free_all;
copied = sg_copy_to_buffer(req->src,
sg_nents_for_len(req->src,
public_key_sz),
public_key, public_key_sz);
if (copied != public_key_sz)
goto free_all;
ret = crypto_ecdh_shared_secret(ctx->curve_id, ctx->ndigits,
ctx->private_key, public_key,
shared_secret);
buf = shared_secret;
} else {
ret = ecc_make_pub_key(ctx->curve_id, ctx->ndigits,
ctx->private_key, public_key);
buf = public_key;
nbytes = public_key_sz;
}
if (ret < 0)
goto free_all;
/* might want less than we've got */
nbytes = min_t(size_t, nbytes, req->dst_len);
copied = sg_copy_from_buffer(req->dst, sg_nents_for_len(req->dst,
nbytes),
buf, nbytes);
if (copied != nbytes)
ret = -EINVAL;
/* fall through */
free_all:
kfree_sensitive(shared_secret);
free_pubkey:
kfree(public_key);
return ret;
}
static unsigned int ecdh_max_size(struct crypto_kpp *tfm)
{
struct ecdh_ctx *ctx = ecdh_get_ctx(tfm);
/* Public key is made of two coordinates, add one to the left shift */
return ctx->ndigits << (ECC_DIGITS_TO_BYTES_SHIFT + 1);
}
static struct kpp_alg ecdh = {
.set_secret = ecdh_set_secret,
.generate_public_key = ecdh_compute_value,
.compute_shared_secret = ecdh_compute_value,
.max_size = ecdh_max_size,
.base = {
.cra_name = "ecdh",
.cra_driver_name = "ecdh-generic",
.cra_priority = 100,
.cra_module = THIS_MODULE,
.cra_ctxsize = sizeof(struct ecdh_ctx),
},
};
static int ecdh_init(void)
{
return crypto_register_kpp(&ecdh);
}
static void ecdh_exit(void)
{
crypto_unregister_kpp(&ecdh);
}
subsys_initcall(ecdh_init);
module_exit(ecdh_exit);
MODULE_ALIAS_CRYPTO("ecdh");
MODULE_LICENSE("GPL");
MODULE_DESCRIPTION("ECDH generic algorithm");