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, 204 insertions, 0 deletions

diff --git a/drivers/input/tablet/kbtab.c b/drivers/input/tablet/kbtab.c
new file mode 100644
index 000000000..6ce70c8e2
--- /dev/null
+++ b/drivers/input/tablet/kbtab.c
@@ -0,0 +1,204 @@
+// SPDX-License-Identifier: GPL-2.0-only
+#include <linux/kernel.h>
+#include <linux/slab.h>
+#include <linux/module.h>
+#include <linux/usb/input.h>
+#include <linux/unaligned.h>
+
+/*
+ * Pressure-threshold modules param code from Alex Perry <alex.perry@ieee.org>
+ */
+
+MODULE_AUTHOR("Josh Myer <josh@joshisanerd.com>");
+MODULE_DESCRIPTION("USB KB Gear JamStudio Tablet driver");
+MODULE_LICENSE("GPL");
+
+#define USB_VENDOR_ID_KBGEAR	0x084e
+
+static int kb_pressure_click = 0x10;
+module_param(kb_pressure_click, int, 0);
+MODULE_PARM_DESC(kb_pressure_click, "pressure threshold for clicks");
+
+struct kbtab {
+	unsigned char *data;
+	dma_addr_t data_dma;
+	struct input_dev *dev;
+	struct usb_interface *intf;
+	struct urb *irq;
+	char phys[32];
+};
+
+static void kbtab_irq(struct urb *urb)
+{
+	struct kbtab *kbtab = urb->context;
+	unsigned char *data = kbtab->data;
+	struct input_dev *dev = kbtab->dev;
+	int pressure;
+	int retval;
+
+	switch (urb->status) {
+	case 0:
+		/* success */
+		break;
+	case -ECONNRESET:
+	case -ENOENT:
+	case -ESHUTDOWN:
+		/* this urb is terminated, clean up */
+		dev_dbg(&kbtab->intf->dev,
+			"%s - urb shutting down with status: %d\n",
+			__func__, urb->status);
+		return;
+	default:
+		dev_dbg(&kbtab->intf->dev,
+			"%s - nonzero urb status received: %d\n",
+			__func__, urb->status);
+		goto exit;
+	}
+
+
+	input_report_key(dev, BTN_TOOL_PEN, 1);
+
+	input_report_abs(dev, ABS_X, get_unaligned_le16(&data[1]));
+	input_report_abs(dev, ABS_Y, get_unaligned_le16(&data[3]));
+
+	/*input_report_key(dev, BTN_TOUCH , data[0] & 0x01);*/
+	input_report_key(dev, BTN_RIGHT, data[0] & 0x02);
+
+	pressure = data[5];
+	if (kb_pressure_click == -1)
+		input_report_abs(dev, ABS_PRESSURE, pressure);
+	else
+		input_report_key(dev, BTN_LEFT, pressure > kb_pressure_click ? 1 : 0);
+
+	input_sync(dev);
+
+ exit:
+	retval = usb_submit_urb(urb, GFP_ATOMIC);
+	if (retval)
+		dev_err(&kbtab->intf->dev,
+			"%s - usb_submit_urb failed with result %d\n",
+			__func__, retval);
+}
+
+static const struct usb_device_id kbtab_ids[] = {
+	{ USB_DEVICE(USB_VENDOR_ID_KBGEAR, 0x1001), .driver_info = 0 },
+	{ }
+};
+
+MODULE_DEVICE_TABLE(usb, kbtab_ids);
+
+static int kbtab_open(struct input_dev *dev)
+{
+	struct kbtab *kbtab = input_get_drvdata(dev);
+	struct usb_device *udev = interface_to_usbdev(kbtab->intf);
+
+	kbtab->irq->dev = udev;
+	if (usb_submit_urb(kbtab->irq, GFP_KERNEL))
+		return -EIO;
+
+	return 0;
+}
+
+static void kbtab_close(struct input_dev *dev)
+{
+	struct kbtab *kbtab = input_get_drvdata(dev);
+
+	usb_kill_urb(kbtab->irq);
+}
+
+static int kbtab_probe(struct usb_interface *intf, const struct usb_device_id *id)
+{
+	struct usb_device *dev = interface_to_usbdev(intf);
+	struct usb_endpoint_descriptor *endpoint;
+	struct kbtab *kbtab;
+	struct input_dev *input_dev;
+	int error = -ENOMEM;
+
+	if (intf->cur_altsetting->desc.bNumEndpoints < 1)
+		return -ENODEV;
+
+	endpoint = &intf->cur_altsetting->endpoint[0].desc;
+	if (!usb_endpoint_is_int_in(endpoint))
+		return -ENODEV;
+
+	kbtab = kzalloc_obj(*kbtab);
+	input_dev = input_allocate_device();
+	if (!kbtab || !input_dev)
+		goto fail1;
+
+	kbtab->data = usb_alloc_coherent(dev, 8, GFP_KERNEL, &kbtab->data_dma);
+	if (!kbtab->data)
+		goto fail1;
+
+	kbtab->irq = usb_alloc_urb(0, GFP_KERNEL);
+	if (!kbtab->irq)
+		goto fail2;
+
+	kbtab->intf = intf;
+	kbtab->dev = input_dev;
+
+	usb_make_path(dev, kbtab->phys, sizeof(kbtab->phys));
+	strlcat(kbtab->phys, "/input0", sizeof(kbtab->phys));
+
+	input_dev->name = "KB Gear Tablet";
+	input_dev->phys = kbtab->phys;
+	usb_to_input_id(dev, &input_dev->id);
+	input_dev->dev.parent = &intf->dev;
+
+	input_set_drvdata(input_dev, kbtab);
+
+	input_dev->open = kbtab_open;
+	input_dev->close = kbtab_close;
+
+	input_dev->evbit[0] |= BIT_MASK(EV_KEY) | BIT_MASK(EV_ABS);
+	input_dev->keybit[BIT_WORD(BTN_LEFT)] |=
+		BIT_MASK(BTN_LEFT) | BIT_MASK(BTN_RIGHT);
+	input_dev->keybit[BIT_WORD(BTN_DIGI)] |=
+		BIT_MASK(BTN_TOOL_PEN) | BIT_MASK(BTN_TOUCH);
+	input_set_abs_params(input_dev, ABS_X, 0, 0x2000, 4, 0);
+	input_set_abs_params(input_dev, ABS_Y, 0, 0x1750, 4, 0);
+	input_set_abs_params(input_dev, ABS_PRESSURE, 0, 0xff, 0, 0);
+
+	usb_fill_int_urb(kbtab->irq, dev,
+			 usb_rcvintpipe(dev, endpoint->bEndpointAddress),
+			 kbtab->data, 8,
+			 kbtab_irq, kbtab, endpoint->bInterval);
+	kbtab->irq->transfer_dma = kbtab->data_dma;
+	kbtab->irq->transfer_flags |= URB_NO_TRANSFER_DMA_MAP;
+
+	error = input_register_device(kbtab->dev);
+	if (error)
+		goto fail3;
+
+	usb_set_intfdata(intf, kbtab);
+
+	return 0;
+
+ fail3:	usb_free_urb(kbtab->irq);
+ fail2:	usb_free_coherent(dev, 8, kbtab->data, kbtab->data_dma);
+ fail1:	input_free_device(input_dev);
+	kfree(kbtab);
+	return error;
+}
+
+static void kbtab_disconnect(struct usb_interface *intf)
+{
+	struct kbtab *kbtab = usb_get_intfdata(intf);
+	struct usb_device *udev = interface_to_usbdev(intf);
+
+	usb_set_intfdata(intf, NULL);
+
+	input_unregister_device(kbtab->dev);
+	usb_free_urb(kbtab->irq);
+	usb_free_coherent(udev, 8, kbtab->data, kbtab->data_dma);
+	kfree(kbtab);
+}
+
+static struct usb_driver kbtab_driver = {
+	.name =		"kbtab",
+	.probe =	kbtab_probe,
+	.disconnect =	kbtab_disconnect,
+	.id_table =	kbtab_ids,
+};
+
+module_usb_driver(kbtab_driver);