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 --- test/fuzz/Makefile | 1 + test/fuzz/virtio.c | 72 ++++++++++++++++++++++++++++++++++++++++++++++ 2 files changed, 73 insertions(+) create mode 100644 test/fuzz/virtio.c
diff --git a/test/fuzz/Makefile b/test/fuzz/Makefile index 03eeeeb497..663b79ce80 100644 --- a/test/fuzz/Makefile +++ b/test/fuzz/Makefile @@ -5,3 +5,4 @@ #
obj-$(CONFIG_$(SPL_)CMDLINE) += cmd_fuzz.o +obj-$(CONFIG_VIRTIO_SANDBOX) += virtio.o diff --git a/test/fuzz/virtio.c b/test/fuzz/virtio.c new file mode 100644 index 0000000000..e5363d5638 --- /dev/null +++ b/test/fuzz/virtio.c @@ -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);