From mboxrd@z Thu Jan 1 00:00:00 1970 Received: from smtp.kernel.org (aws-us-west-2-korg-mail-alma10-1.taild15c8.ts.net [100.103.45.18]) (using TLSv1.2 with cipher ECDHE-RSA-AES256-GCM-SHA384 (256/256 bits)) (No client certificate requested) by smtp.subspace.kernel.org (Postfix) with ESMTPS id 80E74456DF8 for ; Tue, 1 Sep 2026 20:12:08 +0000 (UTC) Authentication-Results: smtp.subspace.kernel.org; arc=none smtp.client-ip=100.103.45.18 ARC-Seal:i=1; a=rsa-sha256; d=subspace.kernel.org; s=arc-20240116; t=1788293534; cv=none; b=qXJm7jFwLjfUH5dpc/Ag3lavJPdm3+8fvUzdyWLSusnlLMULWkgDmRCzk4hBV8dMjC0Q/KmfFcsxIhzouzZ5E14llLrg8nyDhGu4h7AXTtpmU37qILUE7OId/1q4lbuDGI3QLSnAzTy0cKxL5rWONTNqz6Oekhtk9RIcf+MYTU4= ARC-Message-Signature:i=1; a=rsa-sha256; d=subspace.kernel.org; s=arc-20240116; t=1788293534; c=relaxed/simple; bh=lqJpjLgmzuZT92WDBAqIO/yTWdfQviYy1OOcDMI2v4w=; h=From:To:Cc:Subject:Date:Message-ID:In-Reply-To:References: MIME-Version; b=aOOs9YU7x0qQykhggTL5pGYAHZlwSvrennf8hOT/LitYbyoKzcXgu4ShNQSTS0TuGNDOmOHIcSibQIS6r82gRnW2a0btu1KWqtaXJ69Dhgx8Dr61b2byWvTCWP3alcWuSfN47psN2liYkJdz0O34kgcJqp8RlAMSUOg/ZeQFbnA= ARC-Authentication-Results:i=1; smtp.subspace.kernel.org; dkim=pass (2048-bit key) header.d=kernel.org header.i=@kernel.org header.b=irkOTEFR; arc=none smtp.client-ip=100.103.45.18 Authentication-Results: smtp.subspace.kernel.org; dkim=pass (2048-bit key) header.d=kernel.org header.i=@kernel.org header.b="irkOTEFR" Received: by smtp.kernel.org (Postfix) with ESMTPSA id 4C9F11F00A3A; Tue, 1 Sep 2026 20:12:04 +0000 (UTC) DKIM-Signature: v=1; a=rsa-sha256; c=relaxed/relaxed; d=kernel.org; s=k20260515; t=1788293524; bh=MzfDvaWRySApf9CaTZaY1qiWXbSWlaD0WfcYIZyVVyk=; h=From:To:Cc:Subject:Date:In-Reply-To:References; b=irkOTEFRRErIk96XTTz4dozuiTNsudOXbOAohIkYl6dDALqFLzw3ENPrl3ed1FH9B KYDnJOkhYhtYMfk92W361uWgkvOctYw1Fog4aTFK7NM100VuwqIEKRKW8aeFAf8KPn 7K4gNADnEi+Cn3Wi64sP2kVDJH6wI//JdYPr4Smx9wezRKkv/rC+N6/vdioJ3/DU/I PJqiD9Zkap3xne/OnHKAhNEKu7WyIIcBW9Q0MABqx60UTjdN+K19BHYhslfTIQAQ+S +0KPSHfsGRQjfTYycIts6buX/bqd96Vkpv/tAm8frVUbFkBai50sWAf43vCqg84Pgj cNz6QR0wxNAPg== From: Sasha Levin To: stable@vger.kernel.org Cc: Thorsten Blum , Herbert Xu , Sasha Levin Subject: [PATCH 7.2.y 1/2] crypto: atmel-ecc - clean up and improve ECDH comments Date: Tue, 1 Sep 2026 16:12:01 -0400 Message-ID: <20260901201202.1469817-1-sashal@kernel.org> X-Mailer: git-send-email 2.53.0 In-Reply-To: <2026083111-slighting-undergrad-859c@gregkh> References: <2026083111-slighting-undergrad-859c@gregkh> Precedence: bulk X-Mailing-List: stable@vger.kernel.org List-Id: List-Subscribe: List-Unsubscribe: MIME-Version: 1.0 Content-Transfer-Encoding: 8bit From: Thorsten Blum [ Upstream commit 3e84fb698abada239d3e35ed3d52a24dbfda5f6a ] 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 Signed-off-by: Herbert Xu Stable-dep-of: f07a0d251db7 ("crypto: atmel-ecc - avoid stale fallback key after set_secret failure") Signed-off-by: Sasha Levin --- 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 9da9dd6585dfc..87e25696400df 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; -- 2.53.0