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misc: nsm: mark device ready before registering the hwrng and misc device

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nsm_device_probe() registers an hwrng provider and /dev/nsm.
hwrng_register() can make this the current RNG, and the hwrng fill kthread
finds it through the RCU-protected get_current_rng() rather than under the
rng_mutex that hwrng_register() holds, so it can be in nsm_rng_read()
offering buffers and kicking the queue before probe has returned.

The driver never calls virtio_device_ready(), so DRIVER_OK is set on its
behalf by virtio_dev_probe(), only once probe has returned. The virtio
spec is explicit about that ordering in 3.1 Device Initialization:
  |  The driver MUST NOT send any buffer available notifications to the
  |  device before setting DRIVER_OK.

A device that waits for DRIVER_OK before servicing the queue therefore
leaves that read unanswered.

Set DRIVER_OK once the virtqueue exists and before either interface is
registered, so that the queue is usable by the time anything that can reach
it is published; commit f5866db64f ("virtio_console: enable VQs early")
and commit 1d774589f9 ("i2c: virtio: mark device ready before registering
the adapter") do the same for the same reason. The err_hwrng and err_misc
paths then unwind a device that is live, so reset it before deleting the
virtqueue - the core only adds VIRTIO_CONFIG_S_FAILED to the status when
probe fails, it does not reset.

Fixes: b9873755a6 ("misc: Add Nitro Secure Module driver")
Signed-off-by: Jasper Wise <jaspwise@amazon.co.uk>
Link: https://patch.msgid.link/20260813083752.581981-1-jaspwise@amazon.co.uk
Signed-off-by: Greg Kroah-Hartman <gregkh@linuxfoundation.org>
This commit is contained in:
Jasper Wise 2026-08-13 08:37:52 +00:00 committed by Greg Kroah-Hartman
parent 0f3b12bab7
commit e15596e84c
1 changed files with 3 additions and 0 deletions
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3
drivers/misc/nsm.c
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@ -439,6 +439,8 @@ static int nsm_device_probe(struct virtio_device *vdev)
mutex_init(&nsm->lock);
virtio_device_ready(vdev);
/* Register as hwrng provider */
nsm->hwrng = (struct hwrng) {
.read = nsm_rng_read,
@ -471,6 +473,7 @@ static int nsm_device_probe(struct virtio_device *vdev)
err_misc:
hwrng_unregister(&nsm->hwrng);
err_hwrng:
virtio_reset_device(vdev);
vdev->config->del_vqs(vdev);
err_init_vq:
return rc;