x86/kprobes: Fix crash when probing CS CALL instructionsgrafted

When using eBPF to probe CS CALL instructions within a function,
a crash can be triggered.

The eBPF tool probes offset 257 of the __hrtimer_run_queues()
function:

<__hrtimer_run_queues+249>:  nopl   0x0(%rax,%rax,1)
<__hrtimer_run_queues+254>:  mov    %r14,%rdi
<__hrtimer_run_queues+257>:  cs call <__x86_indirect_thunk_r12>
<__hrtimer_run_queues+263>:  mov    %eax,%r12d
<__hrtimer_run_queues+266>:  xchg   %ax,%ax
<__hrtimer_run_queues+268>:  mov    %r13,%rdi

Which triggers this crash:

  BUG: unable to handle page fault for address: 00000000000f41c9
  #PF: supervisor write access in kernel mode
  #PF: error_code(0x0002) - not-present page
  PGD 0 P4D 0
  Oops: 0002 [#1] SMP NOPTI
  CPU: 1 PID: 0 Comm: swapper/1 Kdump: loaded Tainted: P
  RIP: 0010:__hrtimer_run_queues+0x106/0x230

Note that __hrtimer_run_queues+0x106 is __hrtimer_run_queues+262, which is
at the 6th byte of the above CS CALL instruction. Since the CS CALL
instruction occupies 6 bytes, the exception occurred in the middle of that
call instruction.

The root cause is that when using eBPF tools to probe in the middle of a
function, a kprobe with INT3 is used as the underlying implementation.

During single-step emulation of the original CALL instruction,
int3_emulate_call() assumes that the probed CALL instruction is 5 bytes
long. However, the actual CS-prefixed CALL instruction occupies 6 bytes,
so it constructs an incorrect exception return address. When the CPU
returns from the kprobe handler, the next instruction to be executed is at
the address of the last byte of that CS CALL instruction. Coincidentally,
starting from that address, the CPU fetches and decodes a completely
different instruction, which ultimately triggers a kernel crash.

Fix the issue by using the actual instruction length obtained from
the instruction decoder when constructing the exception return
address, rather than relying on the hardcoded CALL_INSN_SIZE macro.

[ mingo: Refined the changelog ]

Fixes: 6256e668b7af ("x86/kprobes: Use int3 instead of debug trap for single-step")
Suggested-by: Masami Hiramatsu (Google) <mhiramat@kernel.org>
Signed-off-by: Jinke Han <jinkehan@didiglobal.com>
Signed-off-by: Ingo Molnar <mingo@kernel.org>
Reviewed-by: Masami Hiramatsu (Google) <mhiramat@kernel.org>
Acked-by: Yafang Shao <laoar.shao@gmail.com>
Acked-by: Borislav Petkov <bp@alien8.de>
Cc: Peter Zijlstra <peterz@infradead.org>
Link: https://patch.msgid.link/20260908073742.GA10517@didi-ThinkCentre-M920t-N000

1 files changed, 743 insertions, 0 deletions

diff --git a/samples/vfio-mdev/mdpy.c b/samples/vfio-mdev/mdpy.c
new file mode 100644
index 000000000..0759bd68e
--- /dev/null
+++ b/samples/vfio-mdev/mdpy.c
@@ -0,0 +1,743 @@
+// SPDX-License-Identifier: GPL-2.0
+/*
+ * Mediated virtual PCI display host device driver
+ *
+ * See mdpy-defs.h for device specs
+ *
+ *   (c) Gerd Hoffmann <kraxel@redhat.com>
+ *
+ * based on mtty driver which is:
+ *   Copyright (c) 2016, NVIDIA CORPORATION. All rights reserved.
+ *	 Author: Neo Jia <cjia@nvidia.com>
+ *		 Kirti Wankhede <kwankhede@nvidia.com>
+ *
+ * This program is free software; you can redistribute it and/or modify
+ * it under the terms of the GNU General Public License version 2 as
+ * published by the Free Software Foundation.
+ */
+#include <linux/init.h>
+#include <linux/module.h>
+#include <linux/kernel.h>
+#include <linux/slab.h>
+#include <linux/vmalloc.h>
+#include <linux/cdev.h>
+#include <linux/vfio.h>
+#include <linux/iommu.h>
+#include <linux/sysfs.h>
+#include <linux/mdev.h>
+#include <linux/pci.h>
+#include <drm/drm_fourcc.h>
+#include "mdpy-defs.h"
+
+#define MDPY_NAME		"mdpy"
+#define MDPY_CLASS_NAME		"mdpy"
+
+#define MDPY_CONFIG_SPACE_SIZE	0xff
+#define MDPY_MEMORY_BAR_OFFSET	PAGE_SIZE
+#define MDPY_DISPLAY_REGION	16
+
+#define STORE_LE16(addr, val)	(*(u16 *)addr = val)
+#define STORE_LE32(addr, val)	(*(u32 *)addr = val)
+
+
+MODULE_DESCRIPTION("Mediated virtual PCI display host device driver");
+MODULE_LICENSE("GPL v2");
+
+#define MDPY_TYPE_1 "vga"
+#define MDPY_TYPE_2 "xga"
+#define MDPY_TYPE_3 "hd"
+
+static struct mdpy_type {
+	struct mdev_type type;
+	u32 format;
+	u32 bytepp;
+	u32 width;
+	u32 height;
+} mdpy_types[] = {
+	{
+		.type.sysfs_name 	= MDPY_TYPE_1,
+		.type.pretty_name	= MDPY_CLASS_NAME "-" MDPY_TYPE_1,
+		.format = DRM_FORMAT_XRGB8888,
+		.bytepp = 4,
+		.width	= 640,
+		.height = 480,
+	}, {
+		.type.sysfs_name 	= MDPY_TYPE_2,
+		.type.pretty_name	= MDPY_CLASS_NAME "-" MDPY_TYPE_2,
+		.format = DRM_FORMAT_XRGB8888,
+		.bytepp = 4,
+		.width	= 1024,
+		.height = 768,
+	}, {
+		.type.sysfs_name 	= MDPY_TYPE_3,
+		.type.pretty_name	= MDPY_CLASS_NAME "-" MDPY_TYPE_3,
+		.format = DRM_FORMAT_XRGB8888,
+		.bytepp = 4,
+		.width	= 1920,
+		.height = 1080,
+	},
+};
+
+static struct mdev_type *mdpy_mdev_types[] = {
+	&mdpy_types[0].type,
+	&mdpy_types[1].type,
+	&mdpy_types[2].type,
+};
+
+static dev_t		mdpy_devt;
+static const struct class mdpy_class = {
+	.name = MDPY_CLASS_NAME,
+};
+static struct cdev	mdpy_cdev;
+static struct device	mdpy_dev;
+static struct mdev_parent mdpy_parent;
+static const struct vfio_device_ops mdpy_dev_ops;
+
+/* State of each mdev device */
+struct mdev_state {
+	struct vfio_device vdev;
+	u8 *vconfig;
+	u32 bar_mask;
+	struct mutex ops_lock;
+	struct mdev_device *mdev;
+	struct vfio_device_info dev_info;
+
+	const struct mdpy_type *type;
+	u32 memsize;
+	void *memblk;
+};
+
+static void mdpy_create_config_space(struct mdev_state *mdev_state)
+{
+	STORE_LE16((u16 *) &mdev_state->vconfig[PCI_VENDOR_ID],
+		   MDPY_PCI_VENDOR_ID);
+	STORE_LE16((u16 *) &mdev_state->vconfig[PCI_DEVICE_ID],
+		   MDPY_PCI_DEVICE_ID);
+	STORE_LE16((u16 *) &mdev_state->vconfig[PCI_SUBSYSTEM_VENDOR_ID],
+		   MDPY_PCI_SUBVENDOR_ID);
+	STORE_LE16((u16 *) &mdev_state->vconfig[PCI_SUBSYSTEM_ID],
+		   MDPY_PCI_SUBDEVICE_ID);
+
+	STORE_LE16((u16 *) &mdev_state->vconfig[PCI_COMMAND],
+		   PCI_COMMAND_IO | PCI_COMMAND_MEMORY);
+	STORE_LE16((u16 *) &mdev_state->vconfig[PCI_STATUS],
+		   PCI_STATUS_CAP_LIST);
+	STORE_LE16((u16 *) &mdev_state->vconfig[PCI_CLASS_DEVICE],
+		   PCI_CLASS_DISPLAY_OTHER);
+	mdev_state->vconfig[PCI_CLASS_REVISION] =  0x01;
+
+	STORE_LE32((u32 *) &mdev_state->vconfig[PCI_BASE_ADDRESS_0],
+		   PCI_BASE_ADDRESS_SPACE_MEMORY |
+		   PCI_BASE_ADDRESS_MEM_TYPE_32	 |
+		   PCI_BASE_ADDRESS_MEM_PREFETCH);
+	mdev_state->bar_mask = ~(mdev_state->memsize) + 1;
+
+	/* vendor specific capability for the config registers */
+	mdev_state->vconfig[PCI_CAPABILITY_LIST]       = MDPY_VENDORCAP_OFFSET;
+	mdev_state->vconfig[MDPY_VENDORCAP_OFFSET + 0] = 0x09; /* vendor cap */
+	mdev_state->vconfig[MDPY_VENDORCAP_OFFSET + 1] = 0x00; /* next ptr */
+	mdev_state->vconfig[MDPY_VENDORCAP_OFFSET + 2] = MDPY_VENDORCAP_SIZE;
+	STORE_LE32((u32 *) &mdev_state->vconfig[MDPY_FORMAT_OFFSET],
+		   mdev_state->type->format);
+	STORE_LE32((u32 *) &mdev_state->vconfig[MDPY_WIDTH_OFFSET],
+		   mdev_state->type->width);
+	STORE_LE32((u32 *) &mdev_state->vconfig[MDPY_HEIGHT_OFFSET],
+		   mdev_state->type->height);
+}
+
+static void handle_pci_cfg_write(struct mdev_state *mdev_state, u16 offset,
+				 char *buf, u32 count)
+{
+	struct device *dev = mdev_dev(mdev_state->mdev);
+	u32 cfg_addr;
+
+	switch (offset) {
+	case PCI_BASE_ADDRESS_0:
+		cfg_addr = *(u32 *)buf;
+
+		if (cfg_addr == 0xffffffff) {
+			cfg_addr = (cfg_addr & mdev_state->bar_mask);
+		} else {
+			cfg_addr &= PCI_BASE_ADDRESS_MEM_MASK;
+			if (cfg_addr)
+				dev_info(dev, "BAR0 @ 0x%x\n", cfg_addr);
+		}
+
+		cfg_addr |= (mdev_state->vconfig[offset] &
+			     ~PCI_BASE_ADDRESS_MEM_MASK);
+		STORE_LE32(&mdev_state->vconfig[offset], cfg_addr);
+		break;
+	}
+}
+
+static ssize_t mdev_access(struct mdev_state *mdev_state, char *buf,
+			   size_t count, loff_t pos, bool is_write)
+{
+	int ret = 0;
+
+	mutex_lock(&mdev_state->ops_lock);
+
+	if (pos < MDPY_CONFIG_SPACE_SIZE) {
+		if (is_write)
+			handle_pci_cfg_write(mdev_state, pos, buf, count);
+		else
+			memcpy(buf, (mdev_state->vconfig + pos), count);
+
+	} else if ((pos >= MDPY_MEMORY_BAR_OFFSET) &&
+		   (pos + count <=
+		    MDPY_MEMORY_BAR_OFFSET + mdev_state->memsize)) {
+		pos -= MDPY_MEMORY_BAR_OFFSET;
+		if (is_write)
+			memcpy(mdev_state->memblk, buf, count);
+		else
+			memcpy(buf, mdev_state->memblk, count);
+
+	} else {
+		dev_info(mdev_state->vdev.dev,
+			 "%s: %s @0x%llx (unhandled)\n", __func__,
+			 is_write ? "WR" : "RD", pos);
+		ret = -1;
+		goto accessfailed;
+	}
+
+	ret = count;
+
+
+accessfailed:
+	mutex_unlock(&mdev_state->ops_lock);
+
+	return ret;
+}
+
+static int mdpy_reset(struct mdev_state *mdev_state)
+{
+	u32 stride, i;
+
+	/* initialize with gray gradient */
+	stride = mdev_state->type->width * mdev_state->type->bytepp;
+	for (i = 0; i < mdev_state->type->height; i++)
+		memset(mdev_state->memblk + i * stride,
+		       i * 255 / mdev_state->type->height,
+		       stride);
+	return 0;
+}
+
+static int mdpy_init_dev(struct vfio_device *vdev)
+{
+	struct mdev_state *mdev_state =
+		container_of(vdev, struct mdev_state, vdev);
+	struct mdev_device *mdev = to_mdev_device(vdev->dev);
+	const struct mdpy_type *type =
+		container_of(mdev->type, struct mdpy_type, type);
+	u32 fbsize;
+	int ret = -ENOMEM;
+
+	mdev_state->vconfig = kzalloc(MDPY_CONFIG_SPACE_SIZE, GFP_KERNEL);
+	if (!mdev_state->vconfig)
+		return ret;
+
+	fbsize = roundup_pow_of_two(type->width * type->height * type->bytepp);
+
+	mdev_state->memblk = vmalloc_user(fbsize);
+	if (!mdev_state->memblk)
+		goto out_vconfig;
+
+	mutex_init(&mdev_state->ops_lock);
+	mdev_state->mdev = mdev;
+	mdev_state->type = type;
+	mdev_state->memsize = fbsize;
+	mdpy_create_config_space(mdev_state);
+	mdpy_reset(mdev_state);
+
+	dev_info(vdev->dev, "%s: %s (%dx%d)\n", __func__, type->type.pretty_name,
+		 type->width, type->height);
+	return 0;
+
+out_vconfig:
+	kfree(mdev_state->vconfig);
+	return ret;
+}
+
+static int mdpy_probe(struct mdev_device *mdev)
+{
+	struct mdev_state *mdev_state;
+	int ret;
+
+	mdev_state = vfio_alloc_device(mdev_state, vdev, &mdev->dev,
+				       &mdpy_dev_ops);
+	if (IS_ERR(mdev_state))
+		return PTR_ERR(mdev_state);
+
+	ret = vfio_register_emulated_iommu_dev(&mdev_state->vdev);
+	if (ret)
+		goto err_put_vdev;
+	dev_set_drvdata(&mdev->dev, mdev_state);
+	return 0;
+
+err_put_vdev:
+	vfio_put_device(&mdev_state->vdev);
+	return ret;
+}
+
+static void mdpy_release_dev(struct vfio_device *vdev)
+{
+	struct mdev_state *mdev_state =
+		container_of(vdev, struct mdev_state, vdev);
+
+	vfree(mdev_state->memblk);
+	kfree(mdev_state->vconfig);
+}
+
+static void mdpy_remove(struct mdev_device *mdev)
+{
+	struct mdev_state *mdev_state = dev_get_drvdata(&mdev->dev);
+
+	dev_info(&mdev->dev, "%s\n", __func__);
+
+	vfio_unregister_group_dev(&mdev_state->vdev);
+	vfio_put_device(&mdev_state->vdev);
+}
+
+static ssize_t mdpy_read(struct vfio_device *vdev, char __user *buf,
+			 size_t count, loff_t *ppos)
+{
+	struct mdev_state *mdev_state =
+		container_of(vdev, struct mdev_state, vdev);
+	unsigned int done = 0;
+	int ret;
+
+	while (count) {
+		size_t filled;
+
+		if (count >= 4 && !(*ppos % 4)) {
+			u32 val;
+
+			ret = mdev_access(mdev_state, (char *)&val, sizeof(val),
+					  *ppos, false);
+			if (ret <= 0)
+				goto read_err;
+
+			if (copy_to_user(buf, &val, sizeof(val)))
+				goto read_err;
+
+			filled = 4;
+		} else if (count >= 2 && !(*ppos % 2)) {
+			u16 val;
+
+			ret = mdev_access(mdev_state, (char *)&val, sizeof(val),
+					  *ppos, false);
+			if (ret <= 0)
+				goto read_err;
+
+			if (copy_to_user(buf, &val, sizeof(val)))
+				goto read_err;
+
+			filled = 2;
+		} else {
+			u8 val;
+
+			ret = mdev_access(mdev_state, (char *)&val, sizeof(val),
+					  *ppos, false);
+			if (ret <= 0)
+				goto read_err;
+
+			if (copy_to_user(buf, &val, sizeof(val)))
+				goto read_err;
+
+			filled = 1;
+		}
+
+		count -= filled;
+		done += filled;
+		*ppos += filled;
+		buf += filled;
+	}
+
+	return done;
+
+read_err:
+	return -EFAULT;
+}
+
+static ssize_t mdpy_write(struct vfio_device *vdev, const char __user *buf,
+			  size_t count, loff_t *ppos)
+{
+	struct mdev_state *mdev_state =
+		container_of(vdev, struct mdev_state, vdev);
+	unsigned int done = 0;
+	int ret;
+
+	while (count) {
+		size_t filled;
+
+		if (count >= 4 && !(*ppos % 4)) {
+			u32 val;
+
+			if (copy_from_user(&val, buf, sizeof(val)))
+				goto write_err;
+
+			ret = mdev_access(mdev_state, (char *)&val, sizeof(val),
+					  *ppos, true);
+			if (ret <= 0)
+				goto write_err;
+
+			filled = 4;
+		} else if (count >= 2 && !(*ppos % 2)) {
+			u16 val;
+
+			if (copy_from_user(&val, buf, sizeof(val)))
+				goto write_err;
+
+			ret = mdev_access(mdev_state, (char *)&val, sizeof(val),
+					  *ppos, true);
+			if (ret <= 0)
+				goto write_err;
+
+			filled = 2;
+		} else {
+			u8 val;
+
+			if (copy_from_user(&val, buf, sizeof(val)))
+				goto write_err;
+
+			ret = mdev_access(mdev_state, (char *)&val, sizeof(val),
+					  *ppos, true);
+			if (ret <= 0)
+				goto write_err;
+
+			filled = 1;
+		}
+		count -= filled;
+		done += filled;
+		*ppos += filled;
+		buf += filled;
+	}
+
+	return done;
+write_err:
+	return -EFAULT;
+}
+
+static int mdpy_mmap(struct vfio_device *vdev, struct vm_area_struct *vma)
+{
+	struct mdev_state *mdev_state =
+		container_of(vdev, struct mdev_state, vdev);
+
+	if (vma->vm_pgoff != MDPY_MEMORY_BAR_OFFSET >> PAGE_SHIFT)
+		return -EINVAL;
+	if (vma->vm_end < vma->vm_start)
+		return -EINVAL;
+	if (vma->vm_end - vma->vm_start > mdev_state->memsize)
+		return -EINVAL;
+	if ((vma->vm_flags & VM_SHARED) == 0)
+		return -EINVAL;
+
+	return remap_vmalloc_range(vma, mdev_state->memblk, 0);
+}
+
+static int mdpy_ioctl_get_region_info(struct vfio_device *vdev,
+				      struct vfio_region_info *region_info,
+				      struct vfio_info_cap *caps)
+{
+	struct mdev_state *mdev_state =
+		container_of(vdev, struct mdev_state, vdev);
+
+	if (region_info->index >= VFIO_PCI_NUM_REGIONS &&
+	    region_info->index != MDPY_DISPLAY_REGION)
+		return -EINVAL;
+
+	switch (region_info->index) {
+	case VFIO_PCI_CONFIG_REGION_INDEX:
+		region_info->offset = 0;
+		region_info->size   = MDPY_CONFIG_SPACE_SIZE;
+		region_info->flags  = (VFIO_REGION_INFO_FLAG_READ |
+				       VFIO_REGION_INFO_FLAG_WRITE);
+		break;
+	case VFIO_PCI_BAR0_REGION_INDEX:
+	case MDPY_DISPLAY_REGION:
+		region_info->offset = MDPY_MEMORY_BAR_OFFSET;
+		region_info->size   = mdev_state->memsize;
+		region_info->flags  = (VFIO_REGION_INFO_FLAG_READ  |
+				       VFIO_REGION_INFO_FLAG_WRITE |
+				       VFIO_REGION_INFO_FLAG_MMAP);
+		break;
+	default:
+		region_info->size   = 0;
+		region_info->offset = 0;
+		region_info->flags  = 0;
+	}
+
+	return 0;
+}
+
+static int mdpy_get_irq_info(struct vfio_irq_info *irq_info)
+{
+	irq_info->count = 0;
+	return 0;
+}
+
+static int mdpy_get_device_info(struct vfio_device_info *dev_info)
+{
+	dev_info->flags = VFIO_DEVICE_FLAGS_PCI;
+	dev_info->num_regions = VFIO_PCI_NUM_REGIONS;
+	dev_info->num_irqs = VFIO_PCI_NUM_IRQS;
+	return 0;
+}
+
+static int mdpy_query_gfx_plane(struct mdev_state *mdev_state,
+				struct vfio_device_gfx_plane_info *plane)
+{
+	if (plane->flags & VFIO_GFX_PLANE_TYPE_PROBE) {
+		if (plane->flags == (VFIO_GFX_PLANE_TYPE_PROBE |
+				     VFIO_GFX_PLANE_TYPE_REGION))
+			return 0;
+		return -EINVAL;
+	}
+
+	if (plane->flags != VFIO_GFX_PLANE_TYPE_REGION)
+		return -EINVAL;
+
+	plane->drm_format     = mdev_state->type->format;
+	plane->width	      = mdev_state->type->width;
+	plane->height	      = mdev_state->type->height;
+	plane->stride	      = (mdev_state->type->width *
+				 mdev_state->type->bytepp);
+	plane->size	      = mdev_state->memsize;
+	plane->region_index   = MDPY_DISPLAY_REGION;
+
+	/* unused */
+	plane->drm_format_mod = 0;
+	plane->x_pos	      = 0;
+	plane->y_pos	      = 0;
+	plane->x_hot	      = 0;
+	plane->y_hot	      = 0;
+
+	return 0;
+}
+
+static long mdpy_ioctl(struct vfio_device *vdev, unsigned int cmd,
+		       unsigned long arg)
+{
+	int ret = 0;
+	unsigned long minsz;
+	struct mdev_state *mdev_state =
+		container_of(vdev, struct mdev_state, vdev);
+
+	switch (cmd) {
+	case VFIO_DEVICE_GET_INFO:
+	{
+		struct vfio_device_info info;
+
+		minsz = offsetofend(struct vfio_device_info, num_irqs);
+
+		if (copy_from_user(&info, (void __user *)arg, minsz))
+			return -EFAULT;
+
+		if (info.argsz < minsz)
+			return -EINVAL;
+
+		ret = mdpy_get_device_info(&info);
+		if (ret)
+			return ret;
+
+		memcpy(&mdev_state->dev_info, &info, sizeof(info));
+
+		if (copy_to_user((void __user *)arg, &info, minsz))
+			return -EFAULT;
+
+		return 0;
+	}
+
+	case VFIO_DEVICE_GET_IRQ_INFO:
+	{
+		struct vfio_irq_info info;
+
+		minsz = offsetofend(struct vfio_irq_info, count);
+
+		if (copy_from_user(&info, (void __user *)arg, minsz))
+			return -EFAULT;
+
+		if ((info.argsz < minsz) ||
+		    (info.index >= mdev_state->dev_info.num_irqs))
+			return -EINVAL;
+
+		ret = mdpy_get_irq_info(&info);
+		if (ret)
+			return ret;
+
+		if (copy_to_user((void __user *)arg, &info, minsz))
+			return -EFAULT;
+
+		return 0;
+	}
+
+	case VFIO_DEVICE_QUERY_GFX_PLANE:
+	{
+		struct vfio_device_gfx_plane_info plane = {};
+
+		minsz = offsetofend(struct vfio_device_gfx_plane_info,
+				    region_index);
+
+		if (copy_from_user(&plane, (void __user *)arg, minsz))
+			return -EFAULT;
+
+		if (plane.argsz < minsz)
+			return -EINVAL;
+
+		ret = mdpy_query_gfx_plane(mdev_state, &plane);
+		if (ret)
+			return ret;
+
+		if (copy_to_user((void __user *)arg, &plane, minsz))
+			return -EFAULT;
+
+		return 0;
+	}
+
+	case VFIO_DEVICE_SET_IRQS:
+		return -EINVAL;
+
+	case VFIO_DEVICE_RESET:
+		return mdpy_reset(mdev_state);
+	}
+	return -ENOTTY;
+}
+
+static ssize_t
+resolution_show(struct device *dev, struct device_attribute *attr,
+		char *buf)
+{
+	struct mdev_state *mdev_state = dev_get_drvdata(dev);
+
+	return sprintf(buf, "%dx%d\n",
+		       mdev_state->type->width,
+		       mdev_state->type->height);
+}
+static DEVICE_ATTR_RO(resolution);
+
+static struct attribute *mdev_dev_attrs[] = {
+	&dev_attr_resolution.attr,
+	NULL,
+};
+
+static const struct attribute_group mdev_dev_group = {
+	.name  = "vendor",
+	.attrs = mdev_dev_attrs,
+};
+
+static const struct attribute_group *mdev_dev_groups[] = {
+	&mdev_dev_group,
+	NULL,
+};
+
+static ssize_t mdpy_show_description(struct mdev_type *mtype, char *buf)
+{
+	struct mdpy_type *type = container_of(mtype, struct mdpy_type, type);
+
+	return sprintf(buf, "virtual display, %dx%d framebuffer\n",
+		       type->width, type->height);
+}
+
+static const struct vfio_device_ops mdpy_dev_ops = {
+	.init = mdpy_init_dev,
+	.release = mdpy_release_dev,
+	.read = mdpy_read,
+	.write = mdpy_write,
+	.ioctl = mdpy_ioctl,
+	.get_region_info_caps = mdpy_ioctl_get_region_info,
+	.mmap = mdpy_mmap,
+	.bind_iommufd	= vfio_iommufd_emulated_bind,
+	.unbind_iommufd	= vfio_iommufd_emulated_unbind,
+	.attach_ioas	= vfio_iommufd_emulated_attach_ioas,
+	.detach_ioas	= vfio_iommufd_emulated_detach_ioas,
+};
+
+static struct mdev_driver mdpy_driver = {
+	.device_api = VFIO_DEVICE_API_PCI_STRING,
+	.max_instances = 4,
+	.driver = {
+		.name = "mdpy",
+		.owner = THIS_MODULE,
+		.mod_name = KBUILD_MODNAME,
+		.dev_groups = mdev_dev_groups,
+	},
+	.probe = mdpy_probe,
+	.remove	= mdpy_remove,
+	.show_description = mdpy_show_description,
+};
+
+static const struct file_operations vd_fops = {
+	.owner		= THIS_MODULE,
+};
+
+static void mdpy_device_release(struct device *dev)
+{
+	/* nothing */
+}
+
+static int __init mdpy_dev_init(void)
+{
+	int ret = 0;
+
+	ret = alloc_chrdev_region(&mdpy_devt, 0, MINORMASK + 1, MDPY_NAME);
+	if (ret < 0) {
+		pr_err("Error: failed to register mdpy_dev, err: %d\n", ret);
+		return ret;
+	}
+	cdev_init(&mdpy_cdev, &vd_fops);
+	cdev_add(&mdpy_cdev, mdpy_devt, MINORMASK + 1);
+	pr_info("%s: major %d\n", __func__, MAJOR(mdpy_devt));
+
+	ret = mdev_register_driver(&mdpy_driver);
+	if (ret)
+		goto err_cdev;
+
+	ret = class_register(&mdpy_class);
+	if (ret)
+		goto err_driver;
+	mdpy_dev.class = &mdpy_class;
+	mdpy_dev.release = mdpy_device_release;
+	dev_set_name(&mdpy_dev, "%s", MDPY_NAME);
+
+	ret = device_register(&mdpy_dev);
+	if (ret)
+		goto err_put;
+
+	ret = mdev_register_parent(&mdpy_parent, &mdpy_dev, &mdpy_driver,
+				   mdpy_mdev_types,
+				   ARRAY_SIZE(mdpy_mdev_types));
+	if (ret)
+		goto err_device;
+
+	return 0;
+
+err_device:
+	device_del(&mdpy_dev);
+err_put:
+	put_device(&mdpy_dev);
+	class_unregister(&mdpy_class);
+err_driver:
+	mdev_unregister_driver(&mdpy_driver);
+err_cdev:
+	cdev_del(&mdpy_cdev);
+	unregister_chrdev_region(mdpy_devt, MINORMASK + 1);
+	return ret;
+}
+
+static void __exit mdpy_dev_exit(void)
+{
+	mdpy_dev.bus = NULL;
+	mdev_unregister_parent(&mdpy_parent);
+
+	device_unregister(&mdpy_dev);
+	mdev_unregister_driver(&mdpy_driver);
+	cdev_del(&mdpy_cdev);
+	unregister_chrdev_region(mdpy_devt, MINORMASK + 1);
+	class_unregister(&mdpy_class);
+}
+
+module_param_named(count, mdpy_driver.max_instances, int, 0444);
+MODULE_PARM_DESC(count, "number of " MDPY_NAME " devices");
+
+module_init(mdpy_dev_init)
+module_exit(mdpy_dev_exit)