From patchwork Thu Jan 19 18:43:47 2023 Content-Type: text/plain; charset="utf-8" MIME-Version: 1.0 Content-Transfer-Encoding: 7bit X-Patchwork-Submitter: Babis Chalios X-Patchwork-Id: 13108509 X-Patchwork-Delegate: herbert@gondor.apana.org.au Return-Path: X-Spam-Checker-Version: SpamAssassin 3.4.0 (2014-02-07) on aws-us-west-2-korg-lkml-1.web.codeaurora.org Received: from vger.kernel.org (vger.kernel.org [23.128.96.18]) by smtp.lore.kernel.org (Postfix) with ESMTP id 579A6C46467 for ; Thu, 19 Jan 2023 18:44:52 +0000 (UTC) Received: (majordomo@vger.kernel.org) by vger.kernel.org via listexpand id S230334AbjASSon (ORCPT ); Thu, 19 Jan 2023 13:44:43 -0500 Received: from lindbergh.monkeyblade.net ([23.128.96.19]:60562 "EHLO lindbergh.monkeyblade.net" rhost-flags-OK-OK-OK-OK) by vger.kernel.org with ESMTP id S230321AbjASSog (ORCPT ); Thu, 19 Jan 2023 13:44:36 -0500 Received: from smtp-fw-9102.amazon.com (smtp-fw-9102.amazon.com [207.171.184.29]) by lindbergh.monkeyblade.net (Postfix) with ESMTPS id EADFE808B2; Thu, 19 Jan 2023 10:44:34 -0800 (PST) DKIM-Signature: v=1; a=rsa-sha256; c=relaxed/relaxed; d=amazon.es; i=@amazon.es; q=dns/txt; s=amazon201209; t=1674153876; x=1705689876; h=from:to:cc:subject:date:message-id:in-reply-to: references:mime-version:content-transfer-encoding; bh=UOgGK+SZ+g6AMbARdW8ck5X612OIHDq9PXzozfjCU/E=; b=F4KwXq5cKCHsE0eQV7kfkKrqTkb8/R6fL6KZt7iq7buaDxP8wkbKnO8b i/KvWD/xn7+LhrUgEO4cKLJs0MREDh/mjjqsH9xv8SnlG+IwrUVE1kYAd v9SBTGVhQ9K6McvL6ULmFE/IFXdISSTpBlvw+m+L1a4k636I2VqOAnu24 s=; X-IronPort-AV: E=Sophos;i="5.97,229,1669075200"; d="scan'208";a="302113438" Received: from pdx4-co-svc-p1-lb2-vlan2.amazon.com (HELO email-inbound-relay-iad-1a-m6i4x-54a853e6.us-east-1.amazon.com) ([10.25.36.210]) by smtp-border-fw-9102.sea19.amazon.com with ESMTP/TLS/ECDHE-RSA-AES256-GCM-SHA384; 19 Jan 2023 18:44:35 +0000 Received: from EX13D50EUB001.ant.amazon.com (iad12-ws-svc-p26-lb9-vlan3.iad.amazon.com [10.40.163.38]) by email-inbound-relay-iad-1a-m6i4x-54a853e6.us-east-1.amazon.com (Postfix) with ESMTPS id CDEB542D52; Thu, 19 Jan 2023 18:44:30 +0000 (UTC) Received: from EX19D037EUB003.ant.amazon.com (10.252.61.119) by EX13D50EUB001.ant.amazon.com (10.43.166.192) with Microsoft SMTP Server (TLS) id 15.0.1497.42; Thu, 19 Jan 2023 18:44:29 +0000 Received: from f4d4887fdcfb.ant.amazon.com (10.43.162.56) by EX19D037EUB003.ant.amazon.com (10.252.61.119) with Microsoft SMTP Server (version=TLS1_2, cipher=TLS_ECDHE_RSA_WITH_AES_256_CBC_SHA384) id 15.2.1118.7; Thu, 19 Jan 2023 18:44:24 +0000 From: Babis Chalios To: Olivia Mackall , Herbert Xu , "Michael S. Tsirkin" , "Jason Wang" , Babis Chalios , , , CC: , , , Subject: [PATCH 1/2] virtio-rng: implement entropy leak feature Date: Thu, 19 Jan 2023 19:43:47 +0100 Message-ID: <20230119184349.74072-2-bchalios@amazon.es> X-Mailer: git-send-email 2.37.1 (Apple Git-137.1) In-Reply-To: <20230119184349.74072-1-bchalios@amazon.es> References: <20230119184349.74072-1-bchalios@amazon.es> MIME-Version: 1.0 X-Originating-IP: [10.43.162.56] X-ClientProxiedBy: EX13D44UWC002.ant.amazon.com (10.43.162.169) To EX19D037EUB003.ant.amazon.com (10.252.61.119) Precedence: bulk List-ID: X-Mailing-List: linux-crypto@vger.kernel.org Implement the virtio-rng feature that allows a guest driver to request from the device to perform certain operations in the event of an "entropy leak", such as when taking a VM snapshot or restoring a VM from a snapshot. The guest can request one of two operations: (i) fill a buffer with random bytes, or (ii) perform a memory copy between two bytes. The feature is similar to Microsoft's Virtual Machine Generation ID and it can be used to (1) avoid the race-condition that exists in our current VMGENID implementation, between the time vcpus are resumed and the ACPI notification is being handled and (2) provide mechanisms for notifying user-space about snapshot-related events. This commit implements the protocol between guest and device. Additionally, it makes sure there is always a request for random bytes in the event of entropy leak in-flight. Once such an event is observed, the driver feeds these bytes to as entropy using `add_device_randomness`. Keep in mind that this commit does not solve the race-condition issue, it adds fresh entropy whenever the driver handles the used buffer from the fill-on-leak request. In order to close the race window, we need to expose some API so that other kernel subsystems can request directly notifications from the device. Signed-off-by: Babis Chalios --- drivers/char/hw_random/virtio-rng.c | 200 +++++++++++++++++++++++++++- include/uapi/linux/virtio_rng.h | 3 + 2 files changed, 197 insertions(+), 6 deletions(-) diff --git a/drivers/char/hw_random/virtio-rng.c b/drivers/char/hw_random/virtio-rng.c index a6f3a8a2aca6..389a091a8801 100644 --- a/drivers/char/hw_random/virtio-rng.c +++ b/drivers/char/hw_random/virtio-rng.c @@ -4,12 +4,14 @@ * Copyright (C) 2007, 2008 Rusty Russell IBM Corporation */ +#include "asm-generic/errno.h" #include #include #include #include #include #include +#include #include #include @@ -18,6 +20,12 @@ static DEFINE_IDA(rng_index_ida); struct virtrng_info { struct hwrng hwrng; struct virtqueue *vq; + /* Leak queues */ + bool has_leakqs; + struct virtqueue *leakq[2]; + spinlock_t lock; + int active_leakq; + char name[25]; int index; bool hwrng_register_done; @@ -29,27 +37,159 @@ struct virtrng_info { /* minimal size returned by rng_buffer_size() */ #if SMP_CACHE_BYTES < 32 u8 data[32]; + u8 leak_data[32]; #else u8 data[SMP_CACHE_BYTES]; + u8 leak_data[SMP_CACHE_BYTES]; #endif }; +/* Swaps the queues and returns the new active leak queue. */ +static struct virtqueue *swap_leakqs(struct virtrng_info *vi) +{ + vi->active_leakq = 1 - vi->active_leakq; + return vi->leakq[vi->active_leakq]; +} + +static struct virtqueue *get_active_leakq(struct virtrng_info *vi) +{ + return vi->leakq[vi->active_leakq]; +} + +int add_fill_on_leak_request(struct virtrng_info *vi, struct virtqueue *vq, void *data, size_t len) +{ + struct scatterlist sg; + int ret; + + sg_init_one(&sg, data, len); + ret = virtqueue_add_inbuf(vq, &sg, 1, data, GFP_KERNEL); + if (ret) + goto err; + +err: + return ret; +} + +int virtrng_fill_on_leak(struct virtrng_info *vi, void *data, size_t len) +{ + struct virtqueue *vq; + unsigned long flags; + int ret; + + if (!vi->has_leakqs) + return -EOPNOTSUPP; + + spin_lock_irqsave(&vi->lock, flags); + + vq = get_active_leakq(vi); + ret = add_fill_on_leak_request(vi, vq, data, len); + if (ret) + virtqueue_kick(vq); + + spin_unlock_irqrestore(&vi->lock, flags); + + return ret; +} + +int add_copy_on_leak_request(struct virtrng_info *vi, struct virtqueue *vq, + void *to, void *from, size_t len) +{ + int ret; + struct scatterlist out, in, *sgs[2]; + + sg_init_one(&out, from, len); + sgs[0] = &out; + sg_init_one(&in, to, len); + sgs[1] = ∈ + + ret = virtqueue_add_sgs(vq, sgs, 1, 1, to, GFP_KERNEL); + if (ret) + goto err; + +err: + return ret; +} + +int virtrng_copy_on_leak(struct virtrng_info *vi, void *to, void *from, size_t len) +{ + struct virtqueue *vq; + unsigned long flags; + int ret; + + if (!vi->has_leakqs) + return -EOPNOTSUPP; + + spin_lock_irqsave(&vi->lock, flags); + + vq = get_active_leakq(vi); + ret = add_copy_on_leak_request(vi, vq, to, from, len); + if (ret) + virtqueue_kick(vq); + + spin_unlock_irqrestore(&vi->lock, flags); + + return ret; +} + +static void entropy_leak_detected(struct virtqueue *vq) +{ + struct virtrng_info *vi = vq->vdev->priv; + struct virtqueue *activeq; + unsigned int len; + unsigned long flags; + void *buffer; + bool kick_activeq = false; + + spin_lock_irqsave(&vi->lock, flags); + + activeq = get_active_leakq(vi); + /* Drain all the used buffers from the queue */ + while ((buffer = virtqueue_get_buf(vq, &len)) != NULL) { + if (vq == activeq) { + pr_debug("%s: entropy leak detected!", vi->name); + activeq = swap_leakqs(vi); + } + + if (buffer == vi->leak_data) { + add_device_randomness(vi->leak_data, sizeof(vi->leak_data)); + + /* Ensure we always have a pending request for random bytes on entropy + * leak. Do it here, after we have swapped leak queues, so it gets handled + * with the next entropy leak event. + */ + add_fill_on_leak_request(vi, activeq, vi->leak_data, sizeof(vi->leak_data)); + kick_activeq = true; + } + } + + if (kick_activeq) + virtqueue_kick(activeq); + + spin_unlock_irqrestore(&vi->lock, flags); +} + static void random_recv_done(struct virtqueue *vq) { struct virtrng_info *vi = vq->vdev->priv; + unsigned long flags; + spin_lock_irqsave(&vi->lock, flags); /* We can get spurious callbacks, e.g. shared IRQs + virtio_pci. */ if (!virtqueue_get_buf(vi->vq, &vi->data_avail)) - return; + goto unlock; vi->data_idx = 0; complete(&vi->have_data); + +unlock: + spin_unlock_irqrestore(&vi->lock, flags); } static void request_entropy(struct virtrng_info *vi) { struct scatterlist sg; + unsigned long flags; reinit_completion(&vi->have_data); vi->data_avail = 0; @@ -57,10 +197,12 @@ static void request_entropy(struct virtrng_info *vi) sg_init_one(&sg, vi->data, sizeof(vi->data)); + spin_lock_irqsave(&vi->lock, flags); /* There should always be room for one buffer. */ virtqueue_add_inbuf(vi->vq, &sg, 1, vi->data, GFP_KERNEL); virtqueue_kick(vi->vq); + spin_unlock_irqrestore(&vi->lock, flags); } static unsigned int copy_data(struct virtrng_info *vi, void *buf, @@ -126,6 +268,40 @@ static void virtio_cleanup(struct hwrng *rng) complete(&vi->have_data); } +static int init_virtqueues(struct virtrng_info *vi, struct virtio_device *vdev) +{ + int ret = -ENOMEM, total_vqs = 1; + struct virtqueue *vqs[3]; + const char *names[3]; + vq_callback_t *callbacks[3]; + + if (vi->has_leakqs) + total_vqs = 3; + + callbacks[0] = random_recv_done; + names[0] = "input"; + if (vi->has_leakqs) { + callbacks[1] = entropy_leak_detected; + names[1] = "leakq.1"; + callbacks[2] = entropy_leak_detected; + names[2] = "leakq.2"; + } + + ret = virtio_find_vqs(vdev, total_vqs, vqs, callbacks, names, NULL); + if (ret) + goto err; + + vi->vq = vqs[0]; + + if (vi->has_leakqs) { + vi->leakq[0] = vqs[1]; + vi->leakq[1] = vqs[2]; + } + +err: + return ret; +} + static int probe_common(struct virtio_device *vdev) { int err, index; @@ -152,18 +328,24 @@ static int probe_common(struct virtio_device *vdev) }; vdev->priv = vi; - /* We expect a single virtqueue. */ - vi->vq = virtio_find_single_vq(vdev, random_recv_done, "input"); - if (IS_ERR(vi->vq)) { - err = PTR_ERR(vi->vq); - goto err_find; + vi->has_leakqs = virtio_has_feature(vdev, VIRTIO_RNG_F_LEAK); + if (vi->has_leakqs) { + spin_lock_init(&vi->lock); + vi->active_leakq = 0; } + err = init_virtqueues(vi, vdev); + if (err) + goto err_find; + virtio_device_ready(vdev); /* we always have a pending entropy request */ request_entropy(vi); + /* we always have a fill_on_leak request pending */ + virtrng_fill_on_leak(vi, vi->leak_data, sizeof(vi->leak_data)); + return 0; err_find: @@ -246,7 +428,13 @@ static const struct virtio_device_id id_table[] = { { 0 }, }; +static unsigned int features[] = { + VIRTIO_RNG_F_LEAK, +}; + static struct virtio_driver virtio_rng_driver = { + .feature_table = features, + .feature_table_size = ARRAY_SIZE(features), .driver.name = KBUILD_MODNAME, .driver.owner = THIS_MODULE, .id_table = id_table, diff --git a/include/uapi/linux/virtio_rng.h b/include/uapi/linux/virtio_rng.h index c4d5de896f0c..d9774951547e 100644 --- a/include/uapi/linux/virtio_rng.h +++ b/include/uapi/linux/virtio_rng.h @@ -5,4 +5,7 @@ #include #include +/* The feature bitmap for virtio entropy device */ +#define VIRTIO_RNG_F_LEAK 0 + #endif /* _LINUX_VIRTIO_RNG_H */