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

3 files changed, 471 insertions, 0 deletions

diff --git a/samples/uhid/.gitignore b/samples/uhid/.gitignore
new file mode 100644
index 000000000..0e0a5a929
--- /dev/null
+++ b/samples/uhid/.gitignore
@@ -0,0 +1,2 @@
+# SPDX-License-Identifier: GPL-2.0-only
+/uhid-example
diff --git a/samples/uhid/Makefile b/samples/uhid/Makefile
new file mode 100644
index 000000000..0aa424ec4
--- /dev/null
+++ b/samples/uhid/Makefile
@@ -0,0 +1,4 @@
+# SPDX-License-Identifier: GPL-2.0-only
+userprogs-always-y += uhid-example
+
+userccflags += -I usr/include
diff --git a/samples/uhid/uhid-example.c b/samples/uhid/uhid-example.c
new file mode 100644
index 000000000..015cb06a2
--- /dev/null
+++ b/samples/uhid/uhid-example.c
@@ -0,0 +1,465 @@
+// SPDX-License-Identifier: GPL-2.0
+/*
+ * UHID Example
+ *
+ * Copyright (c) 2012-2013 David Herrmann <dh.herrmann@gmail.com>
+ *
+ * The code may be used by anyone for any purpose,
+ * and can serve as a starting point for developing
+ * applications using uhid.
+ */
+
+/*
+ * UHID Example
+ * This example emulates a basic 3 buttons mouse with wheel over UHID. Run this
+ * program as root and then use the following keys to control the mouse:
+ *   q: Quit the application
+ *   1: Toggle left button (down, up, ...)
+ *   2: Toggle right button
+ *   3: Toggle middle button
+ *   a: Move mouse left
+ *   d: Move mouse right
+ *   w: Move mouse up
+ *   s: Move mouse down
+ *   r: Move wheel up
+ *   f: Move wheel down
+ *
+ * Additionally to 3 button mouse, 3 keyboard LEDs are also supported (LED_NUML,
+ * LED_CAPSL and LED_SCROLLL). The device doesn't generate any related keyboard
+ * events, though. You need to manually write the EV_LED/LED_XY/1 activation
+ * input event to the evdev device to see it being sent to this device.
+ *
+ * If uhid is not available as /dev/uhid, then you can pass a different path as
+ * first argument.
+ * If <linux/uhid.h> is not installed in /usr, then compile this with:
+ *   gcc -o ./uhid_test -Wall -I./include ./samples/uhid/uhid-example.c
+ * And ignore the warning about kernel headers. However, it is recommended to
+ * use the installed uhid.h if available.
+ */
+
+#include <errno.h>
+#include <fcntl.h>
+#include <poll.h>
+#include <stdbool.h>
+#include <stdio.h>
+#include <stdlib.h>
+#include <string.h>
+#include <termios.h>
+#include <unistd.h>
+#include <linux/uhid.h>
+
+/*
+ * HID Report Desciptor
+ * We emulate a basic 3 button mouse with wheel and 3 keyboard LEDs. This is
+ * the report-descriptor as the kernel will parse it:
+ *
+ * INPUT(1)[INPUT]
+ *   Field(0)
+ *     Physical(GenericDesktop.Pointer)
+ *     Application(GenericDesktop.Mouse)
+ *     Usage(3)
+ *       Button.0001
+ *       Button.0002
+ *       Button.0003
+ *     Logical Minimum(0)
+ *     Logical Maximum(1)
+ *     Report Size(1)
+ *     Report Count(3)
+ *     Report Offset(0)
+ *     Flags( Variable Absolute )
+ *   Field(1)
+ *     Physical(GenericDesktop.Pointer)
+ *     Application(GenericDesktop.Mouse)
+ *     Usage(3)
+ *       GenericDesktop.X
+ *       GenericDesktop.Y
+ *       GenericDesktop.Wheel
+ *     Logical Minimum(-128)
+ *     Logical Maximum(127)
+ *     Report Size(8)
+ *     Report Count(3)
+ *     Report Offset(8)
+ *     Flags( Variable Relative )
+ * OUTPUT(2)[OUTPUT]
+ *   Field(0)
+ *     Application(GenericDesktop.Keyboard)
+ *     Usage(3)
+ *       LED.NumLock
+ *       LED.CapsLock
+ *       LED.ScrollLock
+ *     Logical Minimum(0)
+ *     Logical Maximum(1)
+ *     Report Size(1)
+ *     Report Count(3)
+ *     Report Offset(0)
+ *     Flags( Variable Absolute )
+ *
+ * This is the mapping that we expect:
+ *   Button.0001 ---> Key.LeftBtn
+ *   Button.0002 ---> Key.RightBtn
+ *   Button.0003 ---> Key.MiddleBtn
+ *   GenericDesktop.X ---> Relative.X
+ *   GenericDesktop.Y ---> Relative.Y
+ *   GenericDesktop.Wheel ---> Relative.Wheel
+ *   LED.NumLock ---> LED.NumLock
+ *   LED.CapsLock ---> LED.CapsLock
+ *   LED.ScrollLock ---> LED.ScrollLock
+ *
+ * This information can be verified by reading /sys/kernel/debug/hid/<dev>/rdesc
+ * This file should print the same information as showed above.
+ */
+
+static unsigned char rdesc[] = {
+	0x05, 0x01,	/* USAGE_PAGE (Generic Desktop) */
+	0x09, 0x02,	/* USAGE (Mouse) */
+	0xa1, 0x01,	/* COLLECTION (Application) */
+	0x09, 0x01,		/* USAGE (Pointer) */
+	0xa1, 0x00,		/* COLLECTION (Physical) */
+	0x85, 0x01,			/* REPORT_ID (1) */
+	0x05, 0x09,			/* USAGE_PAGE (Button) */
+	0x19, 0x01,			/* USAGE_MINIMUM (Button 1) */
+	0x29, 0x03,			/* USAGE_MAXIMUM (Button 3) */
+	0x15, 0x00,			/* LOGICAL_MINIMUM (0) */
+	0x25, 0x01,			/* LOGICAL_MAXIMUM (1) */
+	0x95, 0x03,			/* REPORT_COUNT (3) */
+	0x75, 0x01,			/* REPORT_SIZE (1) */
+	0x81, 0x02,			/* INPUT (Data,Var,Abs) */
+	0x95, 0x01,			/* REPORT_COUNT (1) */
+	0x75, 0x05,			/* REPORT_SIZE (5) */
+	0x81, 0x01,			/* INPUT (Cnst,Var,Abs) */
+	0x05, 0x01,			/* USAGE_PAGE (Generic Desktop) */
+	0x09, 0x30,			/* USAGE (X) */
+	0x09, 0x31,			/* USAGE (Y) */
+	0x09, 0x38,			/* USAGE (WHEEL) */
+	0x15, 0x81,			/* LOGICAL_MINIMUM (-127) */
+	0x25, 0x7f,			/* LOGICAL_MAXIMUM (127) */
+	0x75, 0x08,			/* REPORT_SIZE (8) */
+	0x95, 0x03,			/* REPORT_COUNT (3) */
+	0x81, 0x06,			/* INPUT (Data,Var,Rel) */
+	0xc0,			/* END_COLLECTION */
+	0xc0,		/* END_COLLECTION */
+	0x05, 0x01,	/* USAGE_PAGE (Generic Desktop) */
+	0x09, 0x06,	/* USAGE (Keyboard) */
+	0xa1, 0x01,	/* COLLECTION (Application) */
+	0x85, 0x02,		/* REPORT_ID (2) */
+	0x05, 0x08,		/* USAGE_PAGE (Led) */
+	0x19, 0x01,		/* USAGE_MINIMUM (1) */
+	0x29, 0x03,		/* USAGE_MAXIMUM (3) */
+	0x15, 0x00,		/* LOGICAL_MINIMUM (0) */
+	0x25, 0x01,		/* LOGICAL_MAXIMUM (1) */
+	0x95, 0x03,		/* REPORT_COUNT (3) */
+	0x75, 0x01,		/* REPORT_SIZE (1) */
+	0x91, 0x02,		/* Output (Data,Var,Abs) */
+	0x95, 0x01,		/* REPORT_COUNT (1) */
+	0x75, 0x05,		/* REPORT_SIZE (5) */
+	0x91, 0x01,		/* Output (Cnst,Var,Abs) */
+	0xc0,		/* END_COLLECTION */
+};
+
+static int uhid_write(int fd, const struct uhid_event *ev)
+{
+	ssize_t ret;
+
+	ret = write(fd, ev, sizeof(*ev));
+	if (ret < 0) {
+		fprintf(stderr, "Cannot write to uhid: %m\n");
+		return -errno;
+	} else if (ret != sizeof(*ev)) {
+		fprintf(stderr, "Wrong size written to uhid: %zd != %zu\n",
+			ret, sizeof(ev));
+		return -EFAULT;
+	} else {
+		return 0;
+	}
+}
+
+static int create(int fd)
+{
+	struct uhid_event ev;
+
+	memset(&ev, 0, sizeof(ev));
+	ev.type = UHID_CREATE;
+	strcpy((char*)ev.u.create.name, "test-uhid-device");
+	ev.u.create.rd_data = rdesc;
+	ev.u.create.rd_size = sizeof(rdesc);
+	ev.u.create.bus = BUS_USB;
+	ev.u.create.vendor = 0x15d9;
+	ev.u.create.product = 0x0a37;
+	ev.u.create.version = 0;
+	ev.u.create.country = 0;
+
+	return uhid_write(fd, &ev);
+}
+
+static void destroy(int fd)
+{
+	struct uhid_event ev;
+
+	memset(&ev, 0, sizeof(ev));
+	ev.type = UHID_DESTROY;
+
+	uhid_write(fd, &ev);
+}
+
+/* This parses raw output reports sent by the kernel to the device. A normal
+ * uhid program shouldn't do this but instead just forward the raw report.
+ * However, for ducomentational purposes, we try to detect LED events here and
+ * print debug messages for it. */
+static void handle_output(struct uhid_event *ev)
+{
+	/* LED messages are adverised via OUTPUT reports; ignore the rest */
+	if (ev->u.output.rtype != UHID_OUTPUT_REPORT)
+		return;
+	/* LED reports have length 2 bytes */
+	if (ev->u.output.size != 2)
+		return;
+	/* first byte is report-id which is 0x02 for LEDs in our rdesc */
+	if (ev->u.output.data[0] != 0x2)
+		return;
+
+	/* print flags payload */
+	fprintf(stderr, "LED output report received with flags %x\n",
+		ev->u.output.data[1]);
+}
+
+static int event(int fd)
+{
+	struct uhid_event ev;
+	ssize_t ret;
+
+	memset(&ev, 0, sizeof(ev));
+	ret = read(fd, &ev, sizeof(ev));
+	if (ret == 0) {
+		fprintf(stderr, "Read HUP on uhid-cdev\n");
+		return -EFAULT;
+	} else if (ret < 0) {
+		fprintf(stderr, "Cannot read uhid-cdev: %m\n");
+		return -errno;
+	} else if (ret != sizeof(ev)) {
+		fprintf(stderr, "Invalid size read from uhid-dev: %zd != %zu\n",
+			ret, sizeof(ev));
+		return -EFAULT;
+	}
+
+	switch (ev.type) {
+	case UHID_START:
+		fprintf(stderr, "UHID_START from uhid-dev\n");
+		break;
+	case UHID_STOP:
+		fprintf(stderr, "UHID_STOP from uhid-dev\n");
+		break;
+	case UHID_OPEN:
+		fprintf(stderr, "UHID_OPEN from uhid-dev\n");
+		break;
+	case UHID_CLOSE:
+		fprintf(stderr, "UHID_CLOSE from uhid-dev\n");
+		break;
+	case UHID_OUTPUT:
+		fprintf(stderr, "UHID_OUTPUT from uhid-dev\n");
+		handle_output(&ev);
+		break;
+	case UHID_OUTPUT_EV:
+		fprintf(stderr, "UHID_OUTPUT_EV from uhid-dev\n");
+		break;
+	default:
+		fprintf(stderr, "Invalid event from uhid-dev: %u\n", ev.type);
+	}
+
+	return 0;
+}
+
+static bool btn1_down;
+static bool btn2_down;
+static bool btn3_down;
+static signed char abs_hor;
+static signed char abs_ver;
+static signed char wheel;
+
+static int send_event(int fd)
+{
+	struct uhid_event ev;
+
+	memset(&ev, 0, sizeof(ev));
+	ev.type = UHID_INPUT;
+	ev.u.input.size = 5;
+
+	ev.u.input.data[0] = 0x1;
+	if (btn1_down)
+		ev.u.input.data[1] |= 0x1;
+	if (btn2_down)
+		ev.u.input.data[1] |= 0x2;
+	if (btn3_down)
+		ev.u.input.data[1] |= 0x4;
+
+	ev.u.input.data[2] = abs_hor;
+	ev.u.input.data[3] = abs_ver;
+	ev.u.input.data[4] = wheel;
+
+	return uhid_write(fd, &ev);
+}
+
+static int keyboard(int fd)
+{
+	char buf[128];
+	ssize_t ret, i;
+
+	ret = read(STDIN_FILENO, buf, sizeof(buf));
+	if (ret == 0) {
+		fprintf(stderr, "Read HUP on stdin\n");
+		return -EFAULT;
+	} else if (ret < 0) {
+		fprintf(stderr, "Cannot read stdin: %m\n");
+		return -errno;
+	}
+
+	for (i = 0; i < ret; ++i) {
+		switch (buf[i]) {
+		case '1':
+			btn1_down = !btn1_down;
+			ret = send_event(fd);
+			if (ret)
+				return ret;
+			break;
+		case '2':
+			btn2_down = !btn2_down;
+			ret = send_event(fd);
+			if (ret)
+				return ret;
+			break;
+		case '3':
+			btn3_down = !btn3_down;
+			ret = send_event(fd);
+			if (ret)
+				return ret;
+			break;
+		case 'a':
+			abs_hor = -20;
+			ret = send_event(fd);
+			abs_hor = 0;
+			if (ret)
+				return ret;
+			break;
+		case 'd':
+			abs_hor = 20;
+			ret = send_event(fd);
+			abs_hor = 0;
+			if (ret)
+				return ret;
+			break;
+		case 'w':
+			abs_ver = -20;
+			ret = send_event(fd);
+			abs_ver = 0;
+			if (ret)
+				return ret;
+			break;
+		case 's':
+			abs_ver = 20;
+			ret = send_event(fd);
+			abs_ver = 0;
+			if (ret)
+				return ret;
+			break;
+		case 'r':
+			wheel = 1;
+			ret = send_event(fd);
+			wheel = 0;
+			if (ret)
+				return ret;
+			break;
+		case 'f':
+			wheel = -1;
+			ret = send_event(fd);
+			wheel = 0;
+			if (ret)
+				return ret;
+			break;
+		case 'q':
+			return -ECANCELED;
+		default:
+			fprintf(stderr, "Invalid input: %c\n", buf[i]);
+		}
+	}
+
+	return 0;
+}
+
+int main(int argc, char **argv)
+{
+	int fd;
+	const char *path = "/dev/uhid";
+	struct pollfd pfds[2];
+	int ret;
+	struct termios state;
+
+	ret = tcgetattr(STDIN_FILENO, &state);
+	if (ret) {
+		fprintf(stderr, "Cannot get tty state\n");
+	} else {
+		state.c_lflag &= ~ICANON;
+		state.c_cc[VMIN] = 1;
+		ret = tcsetattr(STDIN_FILENO, TCSANOW, &state);
+		if (ret)
+			fprintf(stderr, "Cannot set tty state\n");
+	}
+
+	if (argc >= 2) {
+		if (!strcmp(argv[1], "-h") || !strcmp(argv[1], "--help")) {
+			fprintf(stderr, "Usage: %s [%s]\n", argv[0], path);
+			return EXIT_SUCCESS;
+		} else {
+			path = argv[1];
+		}
+	}
+
+	fprintf(stderr, "Open uhid-cdev %s\n", path);
+	fd = open(path, O_RDWR | O_CLOEXEC);
+	if (fd < 0) {
+		fprintf(stderr, "Cannot open uhid-cdev %s: %m\n", path);
+		return EXIT_FAILURE;
+	}
+
+	fprintf(stderr, "Create uhid device\n");
+	ret = create(fd);
+	if (ret) {
+		close(fd);
+		return EXIT_FAILURE;
+	}
+
+	pfds[0].fd = STDIN_FILENO;
+	pfds[0].events = POLLIN;
+	pfds[1].fd = fd;
+	pfds[1].events = POLLIN;
+
+	fprintf(stderr, "Press 'q' to quit...\n");
+	while (1) {
+		ret = poll(pfds, 2, -1);
+		if (ret < 0) {
+			fprintf(stderr, "Cannot poll for fds: %m\n");
+			break;
+		}
+		if (pfds[0].revents & POLLHUP) {
+			fprintf(stderr, "Received HUP on stdin\n");
+			break;
+		}
+		if (pfds[1].revents & POLLHUP) {
+			fprintf(stderr, "Received HUP on uhid-cdev\n");
+			break;
+		}
+
+		if (pfds[0].revents & POLLIN) {
+			ret = keyboard(fd);
+			if (ret)
+				break;
+		}
+		if (pfds[1].revents & POLLIN) {
+			ret = event(fd);
+			if (ret)
+				break;
+		}
+	}
+
+	fprintf(stderr, "Destroy uhid device\n");
+	destroy(fd);
+	return EXIT_SUCCESS;
+}