Hi Tudor,
> That Bluetooth SMP knows about the private key is pointless, since the
> detection of debug key usage is actually via the public key portion.
> With this patch, the Bluetooth SMP will stop keeping a copy of the
> ecdh private key and will let the crypto subsystem to generate and
> handle the ecdh private key, potentially benefiting of hardware
> ecc private key generation and retention.
>
> The loop that tries to generate a correct private key is now removed and
> we trust the crypto subsystem to generate a correct private key. This
> backup logic should be done in crypto, if really needed.
>
> Signed-off-by: Tudor Ambarus <tudor.amba...@microchip.com>
> ---
> net/bluetooth/ecdh_helper.c | 186 ++++++++++++++++++++++++--------------------
> net/bluetooth/ecdh_helper.h | 9 ++-
> net/bluetooth/selftest.c | 14 +++-
> net/bluetooth/smp.c | 66 +++++++---------
> 4 files changed, 147 insertions(+), 128 deletions(-)
>
> diff --git a/net/bluetooth/ecdh_helper.c b/net/bluetooth/ecdh_helper.c
> index 16e022f..2155ce8 100644
> --- a/net/bluetooth/ecdh_helper.c
> +++ b/net/bluetooth/ecdh_helper.c
> @@ -49,15 +49,21 @@ static inline void swap_digits(u64 *in, u64 *out,
> unsigned int ndigits)
> out[i] = __swab64(in[ndigits - 1 - i]);
> }
>
> +/* compute_ecdh_secret() - function assumes that the private key was
> + * already set.
> + * @tfm: KPP tfm handle allocated with crypto_alloc_kpp().
> + * @public_key: pair's ecc public key.
> + * secret: memory where the ecdh computed shared secret will be saved.
> + *
> + * Return: zero on success; error code in case of error.
> + */
> int compute_ecdh_secret(struct crypto_kpp *tfm, const u8 public_key[64],
> - const u8 private_key[32], u8 secret[32])
> + u8 secret[32])
> {
> struct kpp_request *req;
> - struct ecdh p;
> + u8 *tmp;
> struct ecdh_completion result;
> struct scatterlist src, dst;
> - u8 *tmp, *buf;
> - unsigned int buf_len;
> int err;
>
> tmp = kmalloc(64, GFP_KERNEL);
> @@ -72,28 +78,6 @@ int compute_ecdh_secret(struct crypto_kpp *tfm, const u8
> public_key[64],
>
> init_completion(&result.completion);
>
> - /* Security Manager Protocol holds digits in litte-endian order
> - * while ECC API expect big-endian data
> - */
> - swap_digits((u64 *)private_key, (u64 *)tmp, 4);
> - p.key = (char *)tmp;
> - p.key_size = 32;
> - /* Set curve_id */
> - p.curve_id = ECC_CURVE_NIST_P256;
> - buf_len = crypto_ecdh_key_len(&p);
> - buf = kmalloc(buf_len, GFP_KERNEL);
> - if (!buf) {
> - err = -ENOMEM;
> - goto free_req;
> - }
> -
> - crypto_ecdh_encode_key(buf, buf_len, &p);
> -
> - /* Set A private Key */
> - err = crypto_kpp_set_secret(tfm, (void *)buf, buf_len);
> - if (err)
> - goto free_all;
> -
> swap_digits((u64 *)public_key, (u64 *)tmp, 4); /* x */
> swap_digits((u64 *)&public_key[32], (u64 *)&tmp[32], 4); /* y */
>
> @@ -118,26 +102,76 @@ int compute_ecdh_secret(struct crypto_kpp *tfm, const
> u8 public_key[64],
> memcpy(secret, tmp, 32);
>
> free_all:
> - kzfree(buf);
> -free_req:
> kpp_request_free(req);
> free_tmp:
> kzfree(tmp);
> return err;
> }
>
> -int generate_ecdh_keys(struct crypto_kpp *tfm, u8 public_key[64],
> - u8 private_key[32])
> +/* set_ecdh_privkey() - set or generate ecc private key.
> + *
> + * Function generates an ecc private key in the crypto subsystem when
> receiving
> + * a NULL private key or sets the received key when not NULL.
> + *
> + * @tfm: KPP tfm handle allocated with crypto_alloc_kpp().
> + * @private_key: user's ecc private key. When not NULL, the key is expected
> + * in little endian format.
> + *
> + * Return: zero on success; error code in case of error.
> + */
> +int set_ecdh_privkey(struct crypto_kpp *tfm, const u8 private_key[32])
> +{
> + u8 *buf, *tmp = NULL;
> + unsigned int buf_len;
> + int err;
> + struct ecdh p = {0};
> +
> + p.curve_id = ECC_CURVE_NIST_P256;
> +
> + if (private_key) {
> + tmp = kmalloc(32, GFP_KERNEL);
> + if (!tmp)
> + return -ENOMEM;
> + swap_digits((u64 *)private_key, (u64 *)tmp, 4);
> + p.key = tmp;
> + p.key_size = 32;
> + }
> +
> + buf_len = crypto_ecdh_key_len(&p);
> + buf = kmalloc(buf_len, GFP_KERNEL);
> + if (!buf) {
> + err = -ENOMEM;
> + goto free_tmp;
> + }
> +
> + err = crypto_ecdh_encode_key(buf, buf_len, &p);
> + if (err)
> + goto free_all;
> +
> + err = crypto_kpp_set_secret(tfm, buf, buf_len);
> + /* fall through */
> +free_all:
> + kzfree(buf);
> +free_tmp:
> + kzfree(tmp);
> + return err;
> +}
> +
> +/* generate_ecdh_public_key() - function assumes that the private key was
> + * already set.
> + *
> + * @tfm: KPP tfm handle allocated with crypto_alloc_kpp().
> + * @public_key: memory where the computed ecc public key will be saved.
> + *
> + * Return: zero on success; error code in case of error.
> + */
> +int generate_ecdh_public_key(struct crypto_kpp *tfm, u8 public_key[64])
> {
> struct kpp_request *req;
> - struct ecdh p;
> + u8 *tmp;
> struct ecdh_completion result;
> struct scatterlist dst;
> - u8 *tmp, *buf;
> - unsigned int buf_len;
> int err;
> - const unsigned short max_tries = 16;
> - unsigned short tries = 0;
>
> tmp = kmalloc(64, GFP_KERNEL);
> if (!tmp)
> @@ -150,63 +184,47 @@ int generate_ecdh_keys(struct crypto_kpp *tfm, u8
> public_key[64],
> }
>
> init_completion(&result.completion);
> + sg_init_one(&dst, tmp, 64);
> + kpp_request_set_input(req, NULL, 0);
> + kpp_request_set_output(req, &dst, 64);
> + kpp_request_set_callback(req, CRYPTO_TFM_REQ_MAY_BACKLOG,
> + ecdh_complete, &result);
>
> - /* Set curve_id */
> - p.curve_id = ECC_CURVE_NIST_P256;
> - p.key_size = 32;
> - buf_len = crypto_ecdh_key_len(&p);
> - buf = kmalloc(buf_len, GFP_KERNEL);
> - if (!buf)
> - goto free_req;
> -
> - do {
> - if (tries++ >= max_tries)
> - goto free_all;
> -
> - /* Set private Key */
> - p.key = (char *)private_key;
> - crypto_ecdh_encode_key(buf, buf_len, &p);
> - err = crypto_kpp_set_secret(tfm, buf, buf_len);
> - if (err)
> - goto free_all;
> -
> - sg_init_one(&dst, tmp, 64);
> - kpp_request_set_input(req, NULL, 0);
> - kpp_request_set_output(req, &dst, 64);
> - kpp_request_set_callback(req, CRYPTO_TFM_REQ_MAY_BACKLOG,
> - ecdh_complete, &result);
> -
> - err = crypto_kpp_generate_public_key(req);
> -
> - if (err == -EINPROGRESS) {
> - wait_for_completion(&result.completion);
> - err = result.err;
> - }
> -
> - /* Private key is not valid. Regenerate */
> - if (err == -EINVAL)
> - continue;
> -
> - if (err < 0)
> - goto free_all;
> - else
> - break;
> -
> - } while (true);
> -
> - /* Keys are handed back in little endian as expected by Security
> - * Manager Protocol
> + err = crypto_kpp_generate_public_key(req);
> + if (err == -EINPROGRESS) {
> + wait_for_completion(&result.completion);
> + err = result.err;
> + }
> + if (err < 0)
> + goto free_all;
> +
> + /* The public key is handed back in little endian as expected by
> + * the Security Manager Protocol.
> */
> swap_digits((u64 *)tmp, (u64 *)public_key, 4); /* x */
> swap_digits((u64 *)&tmp[32], (u64 *)&public_key[32], 4); /* y */
> - swap_digits((u64 *)private_key, (u64 *)tmp, 4);
> - memcpy(private_key, tmp, 32);
>
> free_all:
> - kzfree(buf);
> -free_req:
> kpp_request_free(req);
> free_tmp:
> kfree(tmp);
> return err;
> }
> +
> +/* generate_ecdh_keys() - generate ecc key pair.
> + *
> + * @tfm: KPP tfm handle allocated with crypto_alloc_kpp().
> + * @public_key: memory where the computed ecc public key will be saved.
> + *
> + * Return: zero on success; error code in case of error.
> + */
> +int generate_ecdh_keys(struct crypto_kpp *tfm, u8 public_key[64])
> +{
> + int err;
> +
> + err = set_ecdh_privkey(tfm, NULL);
> + if (err)
> + return err;
> +
> + return generate_ecdh_public_key(tfm, public_key);
> +}
> diff --git a/net/bluetooth/ecdh_helper.h b/net/bluetooth/ecdh_helper.h
> index 50e6676..a6f8d03 100644
> --- a/net/bluetooth/ecdh_helper.h
> +++ b/net/bluetooth/ecdh_helper.h
> @@ -23,7 +23,8 @@
> #include <crypto/kpp.h>
> #include <linux/types.h>
>
> -int compute_ecdh_secret(struct crypto_kpp *tfm, const u8 pub_a[64],
> - const u8 priv_b[32], u8 secret[32]);
> -int generate_ecdh_keys(struct crypto_kpp *tfm, u8 public_key[64],
> - u8 private_key[32]);
> +int compute_ecdh_secret(struct crypto_kpp *tfm, const u8 pair_public_key[64],
> + u8 secret[32]);
> +int set_ecdh_privkey(struct crypto_kpp *tfm, const u8 *private_key);
> +int generate_ecdh_public_key(struct crypto_kpp *tfm, u8 public_key[64]);
> +int generate_ecdh_keys(struct crypto_kpp *tfm, u8 public_key[64]);
> diff --git a/net/bluetooth/selftest.c b/net/bluetooth/selftest.c
> index ce99648..2d1519d 100644
> --- a/net/bluetooth/selftest.c
> +++ b/net/bluetooth/selftest.c
> @@ -152,11 +152,11 @@ static int __init test_ecdh_sample(struct crypto_kpp
> *tfm, const u8 priv_a[32],
> dhkey_a = &tmp[0];
> dhkey_b = &tmp[32];
>
> - ret = compute_ecdh_secret(tfm, pub_b, priv_a, dhkey_a);
> + ret = set_ecdh_privkey(tfm, priv_a);
> if (ret)
> goto out;
>
> - ret = compute_ecdh_secret(tfm, pub_a, priv_b, dhkey_b);
> + ret = compute_ecdh_secret(tfm, pub_b, dhkey_a);
> if (ret)
> goto out;
>
> @@ -165,9 +165,17 @@ static int __init test_ecdh_sample(struct crypto_kpp
> *tfm, const u8 priv_a[32],
> goto out;
> }
>
> + ret = set_ecdh_privkey(tfm, priv_b);
> + if (ret)
> + goto out;
> +
> + ret = compute_ecdh_secret(tfm, pub_a, dhkey_b);
> + if (ret)
> + goto out;
> +
> if (memcmp(dhkey_b, dhkey, 32))
> ret = -EINVAL;
> -
> + /* fall through*/
> out:
> kfree(tmp);
> return ret;
> diff --git a/net/bluetooth/smp.c b/net/bluetooth/smp.c
> index af7e610..d41449b 100644
> --- a/net/bluetooth/smp.c
> +++ b/net/bluetooth/smp.c
> @@ -84,7 +84,6 @@ enum {
> struct smp_dev {
> /* Secure Connections OOB data */
> u8 local_pk[64];
> - u8 local_sk[32];
> u8 local_rand[16];
> bool debug_key;
>
> @@ -126,7 +125,6 @@ struct smp_chan {
>
> /* Secure Connections variables */
> u8 local_pk[64];
> - u8 local_sk[32];
> u8 remote_pk[64];
> u8 dhkey[32];
> u8 mackey[16];
> @@ -568,24 +566,22 @@ int smp_generate_oob(struct hci_dev *hdev, u8 hash[16],
> u8 rand[16])
>
> if (hci_dev_test_flag(hdev, HCI_USE_DEBUG_KEYS)) {
> BT_DBG("Using debug keys");
> + err = set_ecdh_privkey(smp->tfm_ecdh, debug_sk);
> + if (err)
> + return err;
> memcpy(smp->local_pk, debug_pk, 64);
> - memcpy(smp->local_sk, debug_sk, 32);
> smp->debug_key = true;
this all looks good, but I do wonder why not have a helper function here.
err = generate_ecdh_debug_keys(smp->tfm_ecdh, smp->local_pk);
And then have that function defined like this:
int generate_ecdh_debug_keys(struct crypto_kpp *tfm, u8 public_key[64])
{
int err;
err = set_ecdh_privkey(tfm, debug_sk);
if (err)
return err;
memcpy(public_key, debug_pk, 64);
return 0;
}
I know this seems duplicate, but I wonder if that reduces the number of
functions that have to be public. I prefer having most function static if
possible.
> } else {
> while (true) {
> - /* Seed private key with random number */
> - get_random_bytes(smp->local_sk, 32);
> -
> - /* Generate local key pair for Secure Connections */
> - err = generate_ecdh_keys(smp->tfm_ecdh, smp->local_pk,
> - smp->local_sk);
> + /* Generate key pair for Secure Connections */
> + err = generate_ecdh_keys(smp->tfm_ecdh, smp->local_pk);
> if (err)
> return err;
>
> /* This is unlikely, but we need to check that
> * we didn't accidentially generate a debug key.
> */
> - if (crypto_memneq(smp->local_sk, debug_sk, 32))
> + if (crypto_memneq(smp->local_pk, debug_pk, 64))
> break;
> }
> smp->debug_key = false;
> @@ -593,7 +589,6 @@ int smp_generate_oob(struct hci_dev *hdev, u8 hash[16],
> u8 rand[16])
>
> SMP_DBG("OOB Public Key X: %32phN", smp->local_pk);
> SMP_DBG("OOB Public Key Y: %32phN", smp->local_pk + 32);
> - SMP_DBG("OOB Private Key: %32phN", smp->local_sk);
>
> get_random_bytes(smp->local_rand, 16);
>
> @@ -1900,7 +1895,6 @@ static u8 sc_send_public_key(struct smp_chan *smp)
> smp_dev = chan->data;
>
> memcpy(smp->local_pk, smp_dev->local_pk, 64);
> - memcpy(smp->local_sk, smp_dev->local_sk, 32);
> memcpy(smp->lr, smp_dev->local_rand, 16);
>
> if (smp_dev->debug_key)
> @@ -1911,23 +1905,20 @@ static u8 sc_send_public_key(struct smp_chan *smp)
>
> if (hci_dev_test_flag(hdev, HCI_USE_DEBUG_KEYS)) {
> BT_DBG("Using debug keys");
> + if (set_ecdh_privkey(smp->tfm_ecdh, debug_sk))
> + return SMP_UNSPECIFIED;
> memcpy(smp->local_pk, debug_pk, 64);
> - memcpy(smp->local_sk, debug_sk, 32);
> set_bit(SMP_FLAG_DEBUG_KEY, &smp->flags);
> } else {
> while (true) {
> - /* Seed private key with random number */
> - get_random_bytes(smp->local_sk, 32);
> -
> - /* Generate local key pair for Secure Connections */
> - if (generate_ecdh_keys(smp->tfm_ecdh, smp->local_pk,
> - smp->local_sk))
> + /* Generate key pair for Secure Connections */
> + if (generate_ecdh_keys(smp->tfm_ecdh, smp->local_pk))
> return SMP_UNSPECIFIED;
>
> /* This is unlikely, but we need to check that
> * we didn't accidentially generate a debug key.
> */
> - if (crypto_memneq(smp->local_sk, debug_sk, 32))
> + if (crypto_memneq(smp->local_pk, debug_pk, 64))
> break;
> }
> }
> @@ -1935,7 +1926,6 @@ static u8 sc_send_public_key(struct smp_chan *smp)
> done:
> SMP_DBG("Local Public Key X: %32phN", smp->local_pk);
> SMP_DBG("Local Public Key Y: %32phN", smp->local_pk + 32);
> - SMP_DBG("Local Private Key: %32phN", smp->local_sk);
>
> smp_send_cmd(smp->conn, SMP_CMD_PUBLIC_KEY, 64, smp->local_pk);
>
> @@ -2663,6 +2653,7 @@ static int smp_cmd_public_key(struct l2cap_conn *conn,
> struct sk_buff *skb)
> struct l2cap_chan *chan = conn->smp;
> struct smp_chan *smp = chan->data;
> struct hci_dev *hdev = hcon->hdev;
> + struct crypto_kpp *tfm_ecdh;
> struct smp_cmd_pairing_confirm cfm;
> int err;
>
> @@ -2695,8 +2686,18 @@ static int smp_cmd_public_key(struct l2cap_conn *conn,
> struct sk_buff *skb)
> SMP_DBG("Remote Public Key X: %32phN", smp->remote_pk);
> SMP_DBG("Remote Public Key Y: %32phN", smp->remote_pk + 32);
>
> - if (!compute_ecdh_secret(smp->tfm_ecdh, smp->remote_pk, smp->local_sk,
> - smp->dhkey))
> + /* Compute the shared secret on the same crypto tfm on which the private
> + * key was set/generated.
> + */
> + if (test_bit(SMP_FLAG_LOCAL_OOB, &smp->flags)) {
> + struct smp_dev *smp_dev = chan->data;
> +
> + tfm_ecdh = smp_dev->tfm_ecdh;
> + } else {
> + tfm_ecdh = smp->tfm_ecdh;
> + }
> +
> + if (compute_ecdh_secret(tfm_ecdh, smp->remote_pk, smp->dhkey))
> return SMP_UNSPECIFIED;
>
> SMP_DBG("DHKey %32phN", smp->dhkey);
> @@ -3522,27 +3523,18 @@ void smp_unregister(struct hci_dev *hdev)
>
> #if IS_ENABLED(CONFIG_BT_SELFTEST_SMP)
>
> -static inline void swap_digits(u64 *in, u64 *out, unsigned int ndigits)
> -{
> - int i;
> -
> - for (i = 0; i < ndigits; i++)
> - out[i] = __swab64(in[ndigits - 1 - i]);
> -}
> -
> static int __init test_debug_key(struct crypto_kpp *tfm_ecdh)
> {
> - u8 pk[64], sk[32];
> + u8 pk[64];
> int err;
>
> - swap_digits((u64 *)debug_sk, (u64 *)sk, 4);
> -
> - err = generate_ecdh_keys(tfm_ecdh, pk, sk);
> + err = set_ecdh_privkey(tfm_ecdh, debug_sk);
> if (err)
> return err;
>
> - if (crypto_memneq(sk, debug_sk, 32))
> - return -EINVAL;
> + err = generate_ecdh_public_key(tfm_ecdh, pk);
> + if (err)
> + return err;
And here using the mentioned generate_ecdh_debug_keys() would make things just
simple as well.
Regards
Marcel
