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fuzz: virtio: Add fuzzer for vring

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Add a fuzzer to test the vring handling code against unexpected
mutations from the virtio device.

After building the sandbox with CONFIG_FUZZ=y, the fuzzer can be invoked
with by:

   UBOOT_SB_FUZZ_TEST=fuzz_vring ./u-boot

This fuzzer finds unvalidated inputs in the vring driver that allow a
buggy or malicious device to make the driver chase wild pointers.

Signed-off-by: Andrew Scull <ascull@google.com>
This commit is contained in:
Andrew Scull 2022-05-30 10:00:13 +00:00 committed by Tom Rini
parent 0518e7a28f
commit a73f3ba91f
2 changed files with 73 additions and 0 deletions
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1
test/fuzz/Makefile
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@ -5,3 +5,4 @@
#
obj-$(CONFIG_$(SPL_)CMDLINE) += cmd_fuzz.o
obj-$(CONFIG_VIRTIO_SANDBOX) += virtio.o

72
test/fuzz/virtio.c Normal file
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@ -0,0 +1,72 @@
/* SPDX-License-Identifier: GPL-2.0+ */
/*
* Copyright (c) 2022 Google, Inc.
* Written by Andrew Scull <ascull@google.com>
*/
#include <common.h>
#include <dm.h>
#include <virtio.h>
#include <virtio_ring.h>
#include <test/fuzz.h>
static int fuzz_vring(const uint8_t *data, size_t size)
{
struct udevice *bus, *dev;
struct virtio_dev_priv *uc_priv;
struct virtqueue *vq;
struct virtio_sg sg[2];
struct virtio_sg *sgs[2];
unsigned int len;
u8 buffer[2][32];
/* hackily hardcode vring sizes */
size_t num = 4;
size_t desc_size = (sizeof(struct vring_desc) * num);
size_t avail_size = (3 + num) * sizeof(u16);
size_t used_size = (3 * sizeof(u16)) + (sizeof(struct vring_used_elem) * num);
if (size < (desc_size + avail_size + used_size))
return 0;
/* check probe success */
if (uclass_first_device(UCLASS_VIRTIO, &bus) || !bus)
panic("Could not find virtio bus\n");
/* check the child virtio-rng device is bound */
if (device_find_first_child(bus, &dev) || !dev)
panic("Could not find virtio device\n");
/*
* fake the virtio device probe by filling in uc_priv->vdev
* which is used by virtio_find_vqs/virtio_del_vqs.
*/
uc_priv = dev_get_uclass_priv(bus);
uc_priv->vdev = dev;
/* prepare the scatter-gather buffer */
sg[0].addr = buffer[0];
sg[0].length = sizeof(buffer[0]);
sg[1].addr = buffer[1];
sg[1].length = sizeof(buffer[1]);
sgs[0] = &sg[0];
sgs[1] = &sg[1];
if (virtio_find_vqs(dev, 1, &vq))
panic("Could not find vqs\n");
if (virtqueue_add(vq, sgs, 0, 1))
panic("Could not add to virtqueue\n");
/* Simulate device writing to vring */
memcpy(vq->vring.desc, data, desc_size);
memcpy(vq->vring.avail, data + desc_size, avail_size);
memcpy(vq->vring.used, data + desc_size + avail_size, used_size);
/* Make sure there is a response */
if (vq->vring.used->idx == 0)
vq->vring.used->idx = 1;
virtqueue_get_buf(vq, &len);
if (virtio_del_vqs(dev))
panic("Could not delete vqs\n");
return 0;
}
FUZZ_TEST(fuzz_vring, 0);