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 AD8D135202B for ; Tue, 1 Sep 2026 21:07:23 +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=1788296844; cv=none; b=sDdzTmrdRdSTZmNVcTDSVVf0HVpIOUwFnCA+C9Geh6kluWdpGm+tX3lsuUsk7xjUuWySD8CBLWqdA9ALLiDF8bh6RjFDjFMhS6aN6HxbSXoicn7B/31uNVfB/GjYMJTfpyKda6Tuq/2FEKaWj86UtACJ8NdDmXjk3TXekrg8Nlo= ARC-Message-Signature:i=1; a=rsa-sha256; d=subspace.kernel.org; s=arc-20240116; t=1788296844; c=relaxed/simple; bh=gQy4mW/NWlh2XOaR1mxrxHX5ZezKztjZRsyL+gSGW8E=; h=From:To:Cc:Subject:Date:Message-ID:In-Reply-To:References: MIME-Version; b=kULJIf+arNGamO1q7ZQqFczHTn7jHXr++931qhRnKKFxVCREWFfD9AeSA2/8J7Eg0q4WqgvCs8d6eFv9rCjGh6zQcluTJUDPfM6d8AqhCWcRdlq5+jKE20xUeb6Rreh0FNyG6pEyYrH0m6FQJ1NaBMSkt5gSKIoZ1O76LqEKFdQ= ARC-Authentication-Results:i=1; smtp.subspace.kernel.org; dkim=pass (2048-bit key) header.d=kernel.org header.i=@kernel.org header.b=CVVIX6BI; 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="CVVIX6BI" Received: by smtp.kernel.org (Postfix) with ESMTPSA id F2FE91F00A3A; Tue, 1 Sep 2026 21:07:22 +0000 (UTC) DKIM-Signature: v=1; a=rsa-sha256; c=relaxed/relaxed; d=kernel.org; s=k20260515; t=1788296843; bh=F9qCC9yQt5O48/snwF3m+fAmhePpp7KYOcyQExGdSvg=; h=From:To:Cc:Subject:Date:In-Reply-To:References; b=CVVIX6BIhX1QtxFeJIrkzuYjOgryISw0iNCus2qBlh2OCXatjJ9Zzf0FleHz1RpPz 73drZ9o3EMCxKjJiy6SOQihE8ZCKh9FBkpEvcB01Yx2Y1s9HhgvodLt4hXKrT3M16r JsmSPEzHwqy/REtxG23PIhiare30AJplzHWdHTX/OOTe01yns6Fsfkcupbps4kKrTX 2VGrjdww7uiuiInSFgP0gJC4+s6ZqoxFVU2zSdafCXg2HhfhR3RfCtgb+xd/X+7QPX BKiy7gVvfXfK3Y15+UsohvJh/V6MXA3IkudPkyjuP2iyDo4zCM0QKwhr7fdHt1bfRI 01wOGqez3kY7Q== From: Sasha Levin To: stable@vger.kernel.org Cc: Thorsten Blum , Herbert Xu , Sasha Levin Subject: [PATCH 7.1.y 2/3] crypto: atmel-ecc - clean up and improve ECDH comments Date: Tue, 1 Sep 2026 17:07:19 -0400 Message-ID: <20260901210720.1603783-2-sashal@kernel.org> X-Mailer: git-send-email 2.53.0 In-Reply-To: <20260901210720.1603783-1-sashal@kernel.org> References: <2026083111-derail-placate-9202@gregkh> <20260901210720.1603783-1-sashal@kernel.org> 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 8160a2c49b10d..8a47ade1a8a71 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