From patchwork Sun Jun 30 19:53:00 2024 Content-Type: text/plain; charset="utf-8" MIME-Version: 1.0 Content-Transfer-Encoding: 8bit X-Patchwork-Submitter: Lukas Wunner X-Patchwork-Id: 13717416 Received: from mailout1.hostsharing.net (mailout1.hostsharing.net [83.223.95.204]) (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 8F1CF3A268; Sun, 30 Jun 2024 20:33:23 +0000 (UTC) Authentication-Results: smtp.subspace.kernel.org; arc=none smtp.client-ip=83.223.95.204 ARC-Seal: i=1; a=rsa-sha256; d=subspace.kernel.org; s=arc-20240116; t=1719779605; cv=none; b=P9oZdDgnu7SI89ATTx9nhFYmehrx2guxShSp+hXflX+bgkEuc7ibne8i7x3yHRvWTOJKLjJqhAiZHXyZ0JRfGDsX3XVfzslzIGPBr0gRD+piop2+sSOiL1eKINHTTBsvUq8uQgPUCW16VT5b9emi5Dt8/YDpz/edgPpo6yjPjtg= ARC-Message-Signature: i=1; a=rsa-sha256; d=subspace.kernel.org; s=arc-20240116; t=1719779605; c=relaxed/simple; bh=7nuE1KfZ+7BNLKWM9fT+4fbsltUVH8PuI92OwB6eteQ=; h=Message-ID:In-Reply-To:References:From:Date:Subject:MIME-Version: Content-Type:To:Cc; b=bY9il4UbsepH1sOch2Di88v1VHHwrsQ31/gllWcC/4ULW8d2a6AAG4LDzTd7PWu0UrtHfoEZUfehGjyWH1y9LfGvBn5Dn8JOdZuX+G6w+50QCe3TF9WIWA6RFWb9Hw0olnysYukaMTu0aQn2t/yUoI0PJFJDF99E/rM57r/hLWM= ARC-Authentication-Results: i=1; smtp.subspace.kernel.org; dmarc=none (p=none dis=none) header.from=wunner.de; spf=pass smtp.mailfrom=wunner.de; arc=none smtp.client-ip=83.223.95.204 Authentication-Results: smtp.subspace.kernel.org; dmarc=none (p=none dis=none) header.from=wunner.de Authentication-Results: smtp.subspace.kernel.org; spf=pass smtp.mailfrom=wunner.de Received: from h08.hostsharing.net (h08.hostsharing.net [83.223.95.28]) (using TLSv1.3 with cipher TLS_AES_256_GCM_SHA384 (256/256 bits) key-exchange X25519 server-signature RSA-PSS (4096 bits) server-digest SHA256 client-signature RSA-PSS (4096 bits) client-digest SHA256) (Client CN "*.hostsharing.net", Issuer "RapidSSL TLS RSA CA G1" (verified OK)) by mailout1.hostsharing.net (Postfix) with ESMTPS id 2A571101917A3; Sun, 30 Jun 2024 22:33:21 +0200 (CEST) Received: from localhost (unknown [89.246.108.87]) (using TLSv1.3 with cipher TLS_AES_256_GCM_SHA384 (256/256 bits) key-exchange ECDHE (prime256v1) server-signature RSA-PSS (4096 bits) server-digest SHA256) (No client certificate requested) by h08.hostsharing.net (Postfix) with ESMTPSA id E400161DA805; Sun, 30 Jun 2024 22:33:20 +0200 (CEST) X-Mailbox-Line: From ee3248f9f8d60cff9106a5a46c5f5d53ac81e60a Mon Sep 17 00:00:00 2001 Message-ID: In-Reply-To: References: From: Lukas Wunner Date: Sun, 30 Jun 2024 21:53:00 +0200 Subject: [PATCH v2 18/18] spdm: Allow control of next requester nonce through sysfs Precedence: bulk X-Mailing-List: linux-cxl@vger.kernel.org List-Id: List-Subscribe: List-Unsubscribe: MIME-Version: 1.0 To: Jonathan Cameron , Bjorn Helgaas , David Howells , Herbert Xu , "David S. Miller" , David Woodhouse , James Bottomley , , , , , Cc: , David Box , Dan Williams , "Li, Ming" , Ilpo Jarvinen , Alistair Francis , Wilfred Mallawa , "Damien Le Moal" , Alexey Kardashevskiy , Dhaval Giani , Gobikrishna Dhanuskodi , Jason Gunthorpe , Peter Gonda , Jerome Glisse , Sean Christopherson , Alexander Graf , Samuel Ortiz , Jonathan Corbet Remote attestation services may mistrust the kernel to always use a fresh nonce for SPDM authentication. So allow user space to set the next requester nonce by writing to a sysfs attribute. Signed-off-by: Lukas Wunner Cc: James Bottomley Cc: Jérôme Glisse Cc: Jason Gunthorpe --- Documentation/ABI/testing/sysfs-devices-spdm | 29 ++++++++++++++++ lib/spdm/core.c | 1 + lib/spdm/req-authenticate.c | 8 ++++- lib/spdm/req-sysfs.c | 35 ++++++++++++++++++++ lib/spdm/spdm.h | 4 +++ 5 files changed, 76 insertions(+), 1 deletion(-) diff --git a/Documentation/ABI/testing/sysfs-devices-spdm b/Documentation/ABI/testing/sysfs-devices-spdm index 5ce34ce10b9c..d315b47b4af0 100644 --- a/Documentation/ABI/testing/sysfs-devices-spdm +++ b/Documentation/ABI/testing/sysfs-devices-spdm @@ -216,3 +216,32 @@ Description: necessary to parse the SPDM messages in the transcript to find and extract the nonces, which is cumbersome. That's why they are exposed as separate files. + + +What: /sys/devices/.../signatures/next_requester_nonce +Date: June 2024 +Contact: Lukas Wunner +Description: + If you do not trust the kernel to always use a fresh nonce, + write 32 bytes to this file to set the requester nonce used + in the next SPDM authentication sequence. + + Meant for remote attestation services. You are responsible + for providing a nonce with sufficient entropy. The kernel + only uses the nonce once, so provide a new one every time + you reauthenticate the device. If you do not provide a + nonce, the kernel generates a random one. + + After the nonce has been consumed, it becomes readable as + the newest [0-9]*_requester_nonce, which proves its usage:: + + # dd if=/dev/random bs=32 count=1 | \ + tee signatures/next_requester_nonce | hexdump + 0000000 e0 77 91 54 bd 56 99 c2 ea 4f 0b 1a 7f ba 6e 59 + 0000010 8f ee f6 b2 26 82 58 34 9e e5 8c 8a 31 58 29 7e + + # echo re > authenticated + + # hexdump $(\ls -t signatures/[0-9]*_requester_nonce | head -1) + 0000000 e0 77 91 54 bd 56 99 c2 ea 4f 0b 1a 7f ba 6e 59 + 0000010 8f ee f6 b2 26 82 58 34 9e e5 8c 8a 31 58 29 7e diff --git a/lib/spdm/core.c b/lib/spdm/core.c index b6a46bdbb2f9..7371adb7a52f 100644 --- a/lib/spdm/core.c +++ b/lib/spdm/core.c @@ -434,6 +434,7 @@ void spdm_destroy(struct spdm_state *spdm_state) spdm_reset(spdm_state); spdm_destroy_log(spdm_state); mutex_destroy(&spdm_state->lock); + kfree(spdm_state->next_nonce); kfree(spdm_state); } EXPORT_SYMBOL_GPL(spdm_destroy); diff --git a/lib/spdm/req-authenticate.c b/lib/spdm/req-authenticate.c index 7c977f5835c1..489fc88de74d 100644 --- a/lib/spdm/req-authenticate.c +++ b/lib/spdm/req-authenticate.c @@ -626,7 +626,13 @@ static int spdm_challenge(struct spdm_state *spdm_state, u8 slot, bool verify) }; int rc, length; - get_random_bytes(&req.nonce, sizeof(req.nonce)); + if (spdm_state->next_nonce) { + memcpy(&req.nonce, spdm_state->next_nonce, sizeof(req.nonce)); + kfree(spdm_state->next_nonce); + spdm_state->next_nonce = NULL; + } else { + get_random_bytes(&req.nonce, sizeof(req.nonce)); + } if (spdm_state->version <= 0x12) req_sz = offsetofend(typeof(req), nonce); diff --git a/lib/spdm/req-sysfs.c b/lib/spdm/req-sysfs.c index c782054f8e18..232d4a00a510 100644 --- a/lib/spdm/req-sysfs.c +++ b/lib/spdm/req-sysfs.c @@ -176,13 +176,48 @@ const struct attribute_group spdm_certificates_group = { /* signatures attributes */ +static umode_t spdm_signatures_are_visible(struct kobject *kobj, + struct bin_attribute *a, int n) +{ + struct device *dev = kobj_to_dev(kobj); + struct spdm_state *spdm_state = dev_to_spdm_state(dev); + + if (IS_ERR_OR_NULL(spdm_state)) + return SYSFS_GROUP_INVISIBLE; + + return a->attr.mode; +} + +static ssize_t next_requester_nonce_write(struct file *file, + struct kobject *kobj, + struct bin_attribute *attr, + char *buf, loff_t off, size_t count) +{ + struct device *dev = kobj_to_dev(kobj); + struct spdm_state *spdm_state = dev_to_spdm_state(dev); + + guard(mutex)(&spdm_state->lock); + + if (!spdm_state->next_nonce) { + spdm_state->next_nonce = kmalloc(SPDM_NONCE_SZ, GFP_KERNEL); + if (!spdm_state->next_nonce) + return -ENOMEM; + } + + memcpy(spdm_state->next_nonce + off, buf, count); + return count; +} +static BIN_ATTR_WO(next_requester_nonce, SPDM_NONCE_SZ); + static struct bin_attribute *spdm_signatures_bin_attrs[] = { + &bin_attr_next_requester_nonce, NULL }; const struct attribute_group spdm_signatures_group = { .name = "signatures", .bin_attrs = spdm_signatures_bin_attrs, + .is_bin_visible = spdm_signatures_are_visible, }; static unsigned int spdm_max_log_sz = SZ_16M; /* per device */ diff --git a/lib/spdm/spdm.h b/lib/spdm/spdm.h index 448107c92db7..aa36aa55e718 100644 --- a/lib/spdm/spdm.h +++ b/lib/spdm/spdm.h @@ -475,6 +475,9 @@ struct spdm_error_rsp { * itself and the transcript with trailing signature. * @log_counter: Number of generated log entries so far. Will be prefixed to * the sysfs files of the next generated log entry. + * @next_nonce: Requester nonce to be used for the next authentication + * sequence. Populated from user space through sysfs. + * If user space does not provide a nonce, the kernel uses a random one. */ struct spdm_state { struct device *dev; @@ -521,6 +524,7 @@ struct spdm_state { struct list_head log; size_t log_sz; u32 log_counter; + u8 *next_nonce; }; extern struct list_head spdm_state_list;