* [PATCH v2 2/2] crypto: atmel-ecc - clean up and improve ECDH comments
2026-06-09 10:05 [PATCH v2 1/2] crypto: atmel-i2c - improve comment in atmel_i2c_init_ecdh_cmd Thorsten Blum
@ 2026-06-09 10:05 ` Thorsten Blum
0 siblings, 0 replies; 2+ messages in thread
From: Thorsten Blum @ 2026-06-09 10:05 UTC (permalink / raw)
To: Thorsten Blum, Herbert Xu, David S. Miller, Nicolas Ferre,
Alexandre Belloni, Claudiu Beznea
Cc: linux-crypto, linux-arm-kernel, linux-kernel
Improve the kerneldoc for struct atmel_ecdh_ctx by removing the stale
"unsupported curves" wording, since the device only supports a single
curve (P-256), and move the set_secret() constraint to the description.
In atmel_ecdh_set_secret(), clarify that the device generates the
private key, and drop the redundant "only supports NIST P256" comment.
In atmel_ecdh_done() and atmel_ecdh_generate_public_key(), clarify the
truncation comments. Also note that a P-256 public key consists of two
32-byte coordinates in atmel_ecdh_compute_shared_secret(), and remove
the unnecessary fall-through comment and other redundant comments.
Signed-off-by: Thorsten Blum <thorsten.blum@linux.dev>
---
Changes in v2:
- Adjust atmel_ecdh_ctx kerneldoc formatting/indentation according to:
https://www.kernel.org/doc/html/latest/doc-guide/kernel-doc.html#members
- v1: https://lore.kernel.org/r/20260603192708.1237715-4-thorsten.blum@linux.dev/
---
drivers/crypto/atmel-ecc.c | 38 ++++++++++++++------------------------
1 file changed, 14 insertions(+), 24 deletions(-)
diff --git a/drivers/crypto/atmel-ecc.c b/drivers/crypto/atmel-ecc.c
index 0ca02995a1de..cd33d3f132cc 100644
--- a/drivers/crypto/atmel-ecc.c
+++ b/drivers/crypto/atmel-ecc.c
@@ -27,15 +27,14 @@ static struct atmel_ecc_driver_data driver_data;
/**
* struct atmel_ecdh_ctx - transformation context
- * @client : pointer to i2c client device
- * @fallback : used for unsupported curves or when user wants to use its own
- * private key.
- * @public_key : generated when calling set_secret(). It's the responsibility
- * of the user to not call set_secret() while
- * generate_public_key() or compute_shared_secret() are in flight.
- * @curve_id : elliptic curve id
- * @do_fallback: true when the device doesn't support the curve or when the user
- * wants to use its own private key.
+ * @client: I2C client device
+ * @fallback: ECDH fallback used for caller-provided private keys
+ * @public_key: cached public key for the device-generated private key
+ * @curve_id: elliptic curve id
+ * @do_fallback: true when ECDH operations should use @fallback
+ *
+ * The caller must not invoke set_secret() while generate_public_key()
+ * or compute_shared_secret() are in flight.
*/
struct atmel_ecdh_ctx {
struct i2c_client *client;
@@ -55,7 +54,7 @@ static void atmel_ecdh_done(struct atmel_i2c_work_data *work_data, void *areq,
if (status)
goto free_work_data;
- /* might want less than we've got */
+ /* copy only as much as requested, capped at 32 bytes */
n_sz = min(ATMEL_ECC_NIST_P256_N_SIZE, req->dst_len);
/* copy the shared secret */
@@ -64,15 +63,15 @@ static void atmel_ecdh_done(struct atmel_i2c_work_data *work_data, void *areq,
if (copied != n_sz)
status = -EINVAL;
- /* fall through */
free_work_data:
kfree_sensitive(work_data);
kpp_request_complete(req, status);
}
/*
- * A random private key is generated and stored in the device. The device
- * returns the pair public key.
+ * If no private key is provided, generate one in the device and cache
+ * the corresponding public key. The generated private key never leaves
+ * the device.
*/
static int atmel_ecdh_set_secret(struct crypto_kpp *tfm, const void *buf,
unsigned int len)
@@ -83,9 +82,7 @@ static int atmel_ecdh_set_secret(struct crypto_kpp *tfm, const void *buf,
struct ecdh params;
int ret = -ENOMEM;
- /* free the old public key, if any */
kfree(ctx->public_key);
- /* make sure you don't free the old public key twice */
ctx->public_key = NULL;
if (crypto_ecdh_decode_key(buf, len, ¶ms) < 0) {
@@ -94,7 +91,6 @@ static int atmel_ecdh_set_secret(struct crypto_kpp *tfm, const void *buf,
}
if (params.key_size) {
- /* fallback to ecdh software implementation */
ctx->do_fallback = true;
return crypto_kpp_set_secret(ctx->fallback, buf, len);
}
@@ -103,11 +99,6 @@ static int atmel_ecdh_set_secret(struct crypto_kpp *tfm, const void *buf,
if (!cmd)
return -ENOMEM;
- /*
- * The device only supports NIST P256 ECC keys. The public key size will
- * always be the same. Use a macro for the key size to avoid unnecessary
- * computations.
- */
public_key = kmalloc(ATMEL_ECC_PUBKEY_SIZE, GFP_KERNEL);
if (!public_key)
goto free_cmd;
@@ -120,7 +111,6 @@ static int atmel_ecdh_set_secret(struct crypto_kpp *tfm, const void *buf,
if (ret)
goto free_public_key;
- /* save the public key */
memcpy(public_key, &cmd->data[RSP_DATA_IDX], ATMEL_ECC_PUBKEY_SIZE);
ctx->public_key = public_key;
@@ -149,7 +139,7 @@ static int atmel_ecdh_generate_public_key(struct kpp_request *req)
if (!ctx->public_key)
return -EINVAL;
- /* might want less than we've got */
+ /* copy only as much as requested, capped at 64 bytes */
nbytes = min(ATMEL_ECC_PUBKEY_SIZE, req->dst_len);
/* public key was saved at private key generation */
@@ -175,7 +165,7 @@ static int atmel_ecdh_compute_shared_secret(struct kpp_request *req)
return crypto_kpp_compute_shared_secret(req);
}
- /* must have exactly two points to be on the curve */
+ /* A P-256 public key must contain two 32-byte coordinates */
if (req->src_len != ATMEL_ECC_PUBKEY_SIZE)
return -EINVAL;
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