On Thu, Jan 19, 2023 at 07:43:47PM +0100, Babis Chalios wrote:
> 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 <bchalios@xxxxxxxxx>
> ---
> 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"
Why are you pulling this in?
If you really need errno the thing to include
is linux/errno.h
checkpatch has a rule to catch such cases:
# warn if <asm/foo.h> is #included and <linux/foo.h> is available and includes
# itself <asm/foo.h> (uses RAW line)
did you run checkpatch?
> #include <linux/err.h>
> #include <linux/hw_random.h>
> #include <linux/scatterlist.h>
> #include <linux/spinlock.h>
> #include <linux/virtio.h>
> #include <linux/virtio_rng.h>
> +#include <linux/random.h>
> #include <linux/module.h>
> #include <linux/slab.h>
>
> @@ -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 <linux/virtio_ids.h>
> #include <linux/virtio_config.h>
>
> +/* The feature bitmap for virtio entropy device */
> +#define VIRTIO_RNG_F_LEAK 0
> +
> #endif /* _LINUX_VIRTIO_RNG_H */
> --
> 2.38.1
>
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