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, 357 insertions, 0 deletions

diff --git a/drivers/leds/trigger/ledtrig-tty.c b/drivers/leds/trigger/ledtrig-tty.c
new file mode 100644
index 000000000..372557114
--- /dev/null
+++ b/drivers/leds/trigger/ledtrig-tty.c
@@ -0,0 +1,357 @@
+// SPDX-License-Identifier: GPL-2.0
+
+#include <linux/completion.h>
+#include <linux/delay.h>
+#include <linux/leds.h>
+#include <linux/module.h>
+#include <linux/slab.h>
+#include <linux/tty.h>
+#include <uapi/linux/serial.h>
+
+#define LEDTRIG_TTY_INTERVAL	50
+
+struct ledtrig_tty_data {
+	struct led_classdev *led_cdev;
+	struct delayed_work dwork;
+	struct completion sysfs;
+	const char *ttyname;
+	struct tty_struct *tty;
+	int rx, tx;
+	bool mode_rx;
+	bool mode_tx;
+	bool mode_cts;
+	bool mode_dsr;
+	bool mode_dcd;
+	bool mode_rng;
+};
+
+/* Indicates which state the LED should now display */
+enum led_trigger_tty_state {
+	TTY_LED_BLINK,
+	TTY_LED_ENABLE,
+	TTY_LED_DISABLE,
+};
+
+enum led_trigger_tty_modes {
+	TRIGGER_TTY_RX = 0,
+	TRIGGER_TTY_TX,
+	TRIGGER_TTY_CTS,
+	TRIGGER_TTY_DSR,
+	TRIGGER_TTY_DCD,
+	TRIGGER_TTY_RNG,
+};
+
+static int ledtrig_tty_wait_for_completion(struct device *dev)
+{
+	struct ledtrig_tty_data *trigger_data = led_trigger_get_drvdata(dev);
+	int ret;
+
+	ret = wait_for_completion_timeout(&trigger_data->sysfs,
+					  msecs_to_jiffies(LEDTRIG_TTY_INTERVAL * 20));
+	if (ret == 0)
+		return -ETIMEDOUT;
+
+	return ret;
+}
+
+static ssize_t ttyname_show(struct device *dev,
+			    struct device_attribute *attr, char *buf)
+{
+	struct ledtrig_tty_data *trigger_data = led_trigger_get_drvdata(dev);
+	ssize_t len = 0;
+	int completion;
+
+	reinit_completion(&trigger_data->sysfs);
+	completion = ledtrig_tty_wait_for_completion(dev);
+	if (completion < 0)
+		return completion;
+
+	if (trigger_data->ttyname)
+		len = sprintf(buf, "%s\n", trigger_data->ttyname);
+
+	return len;
+}
+
+static ssize_t ttyname_store(struct device *dev,
+			     struct device_attribute *attr, const char *buf,
+			     size_t size)
+{
+	struct ledtrig_tty_data *trigger_data = led_trigger_get_drvdata(dev);
+	char *ttyname;
+	ssize_t ret = size;
+	int completion;
+
+	if (size > 0 && buf[size - 1] == '\n')
+		size -= 1;
+
+	if (size) {
+		ttyname = kmemdup_nul(buf, size, GFP_KERNEL);
+		if (!ttyname)
+			return -ENOMEM;
+	} else {
+		ttyname = NULL;
+	}
+
+	reinit_completion(&trigger_data->sysfs);
+	completion = ledtrig_tty_wait_for_completion(dev);
+	if (completion < 0)
+		return completion;
+
+	kfree(trigger_data->ttyname);
+	tty_kref_put(trigger_data->tty);
+	trigger_data->tty = NULL;
+
+	trigger_data->ttyname = ttyname;
+
+	return ret;
+}
+static DEVICE_ATTR_RW(ttyname);
+
+static ssize_t ledtrig_tty_attr_show(struct device *dev, char *buf,
+				     enum led_trigger_tty_modes attr)
+{
+	struct ledtrig_tty_data *trigger_data = led_trigger_get_drvdata(dev);
+	bool state;
+
+	switch (attr) {
+	case TRIGGER_TTY_RX:
+		state = trigger_data->mode_rx;
+		break;
+	case TRIGGER_TTY_TX:
+		state = trigger_data->mode_tx;
+		break;
+	case TRIGGER_TTY_CTS:
+		state = trigger_data->mode_cts;
+		break;
+	case TRIGGER_TTY_DSR:
+		state = trigger_data->mode_dsr;
+		break;
+	case TRIGGER_TTY_DCD:
+		state = trigger_data->mode_dcd;
+		break;
+	case TRIGGER_TTY_RNG:
+		state = trigger_data->mode_rng;
+		break;
+	}
+
+	return sysfs_emit(buf, "%u\n", state);
+}
+
+static ssize_t ledtrig_tty_attr_store(struct device *dev, const char *buf,
+				      size_t size, enum led_trigger_tty_modes attr)
+{
+	struct ledtrig_tty_data *trigger_data = led_trigger_get_drvdata(dev);
+	bool state;
+	int ret;
+
+	ret = kstrtobool(buf, &state);
+	if (ret)
+		return ret;
+
+	switch (attr) {
+	case TRIGGER_TTY_RX:
+		trigger_data->mode_rx = state;
+		break;
+	case TRIGGER_TTY_TX:
+		trigger_data->mode_tx = state;
+		break;
+	case TRIGGER_TTY_CTS:
+		trigger_data->mode_cts = state;
+		break;
+	case TRIGGER_TTY_DSR:
+		trigger_data->mode_dsr = state;
+		break;
+	case TRIGGER_TTY_DCD:
+		trigger_data->mode_dcd = state;
+		break;
+	case TRIGGER_TTY_RNG:
+		trigger_data->mode_rng = state;
+		break;
+	}
+
+	return size;
+}
+
+#define DEFINE_TTY_TRIGGER(trigger_name, trigger) \
+	static ssize_t trigger_name##_show(struct device *dev, \
+		struct device_attribute *attr, char *buf) \
+	{ \
+		return ledtrig_tty_attr_show(dev, buf, trigger); \
+	} \
+	static ssize_t trigger_name##_store(struct device *dev, \
+		struct device_attribute *attr, const char *buf, size_t size) \
+	{ \
+		return ledtrig_tty_attr_store(dev, buf, size, trigger); \
+	} \
+	static DEVICE_ATTR_RW(trigger_name)
+
+DEFINE_TTY_TRIGGER(rx, TRIGGER_TTY_RX);
+DEFINE_TTY_TRIGGER(tx, TRIGGER_TTY_TX);
+DEFINE_TTY_TRIGGER(cts, TRIGGER_TTY_CTS);
+DEFINE_TTY_TRIGGER(dsr, TRIGGER_TTY_DSR);
+DEFINE_TTY_TRIGGER(dcd, TRIGGER_TTY_DCD);
+DEFINE_TTY_TRIGGER(rng, TRIGGER_TTY_RNG);
+
+static void ledtrig_tty_work(struct work_struct *work)
+{
+	struct ledtrig_tty_data *trigger_data =
+		container_of(work, struct ledtrig_tty_data, dwork.work);
+	enum led_trigger_tty_state state = TTY_LED_DISABLE;
+	unsigned long interval = LEDTRIG_TTY_INTERVAL;
+	bool invert = false;
+	int status;
+	int ret;
+
+	if (!trigger_data->ttyname)
+		goto out;
+
+	/* try to get the tty corresponding to $ttyname */
+	if (!trigger_data->tty) {
+		dev_t devno;
+		struct tty_struct *tty;
+		int ret;
+
+		ret = tty_dev_name_to_number(trigger_data->ttyname, &devno);
+		if (ret < 0)
+			/*
+			 * A device with this name might appear later, so keep
+			 * retrying.
+			 */
+			goto out;
+
+		tty = tty_kopen_shared(devno);
+		if (IS_ERR_OR_NULL(tty))
+			/* What to do? retry or abort */
+			goto out;
+
+		trigger_data->tty = tty;
+	}
+
+	status = tty_get_tiocm(trigger_data->tty);
+	if (status > 0) {
+		if (trigger_data->mode_cts) {
+			if (status & TIOCM_CTS)
+				state = TTY_LED_ENABLE;
+		}
+
+		if (trigger_data->mode_dsr) {
+			if (status & TIOCM_DSR)
+				state = TTY_LED_ENABLE;
+		}
+
+		if (trigger_data->mode_dcd) {
+			if (status & TIOCM_CAR)
+				state = TTY_LED_ENABLE;
+		}
+
+		if (trigger_data->mode_rng) {
+			if (status & TIOCM_RNG)
+				state = TTY_LED_ENABLE;
+		}
+	}
+
+	/*
+	 * The evaluation of rx/tx must be done after the evaluation
+	 * of TIOCM_*, because rx/tx has priority.
+	 */
+	if (trigger_data->mode_rx || trigger_data->mode_tx) {
+		struct serial_icounter_struct icount;
+
+		ret = tty_get_icount(trigger_data->tty, &icount);
+		if (ret)
+			goto out;
+
+		if (trigger_data->mode_tx && (icount.tx != trigger_data->tx)) {
+			trigger_data->tx = icount.tx;
+			invert = state == TTY_LED_ENABLE;
+			state = TTY_LED_BLINK;
+		}
+
+		if (trigger_data->mode_rx && (icount.rx != trigger_data->rx)) {
+			trigger_data->rx = icount.rx;
+			invert = state == TTY_LED_ENABLE;
+			state = TTY_LED_BLINK;
+		}
+	}
+
+out:
+	switch (state) {
+	case TTY_LED_BLINK:
+		led_blink_set_oneshot(trigger_data->led_cdev, &interval,
+				&interval, invert);
+		break;
+	case TTY_LED_ENABLE:
+		led_set_brightness(trigger_data->led_cdev,
+				trigger_data->led_cdev->blink_brightness);
+		break;
+	case TTY_LED_DISABLE:
+		fallthrough;
+	default:
+		led_set_brightness(trigger_data->led_cdev, LED_OFF);
+		break;
+	}
+
+	complete_all(&trigger_data->sysfs);
+	schedule_delayed_work(&trigger_data->dwork,
+			      msecs_to_jiffies(LEDTRIG_TTY_INTERVAL * 2));
+}
+
+static struct attribute *ledtrig_tty_attrs[] = {
+	&dev_attr_ttyname.attr,
+	&dev_attr_rx.attr,
+	&dev_attr_tx.attr,
+	&dev_attr_cts.attr,
+	&dev_attr_dsr.attr,
+	&dev_attr_dcd.attr,
+	&dev_attr_rng.attr,
+	NULL
+};
+ATTRIBUTE_GROUPS(ledtrig_tty);
+
+static int ledtrig_tty_activate(struct led_classdev *led_cdev)
+{
+	struct ledtrig_tty_data *trigger_data;
+
+	trigger_data = kzalloc_obj(*trigger_data);
+	if (!trigger_data)
+		return -ENOMEM;
+
+	/* Enable default rx/tx mode */
+	trigger_data->mode_rx = true;
+	trigger_data->mode_tx = true;
+
+	led_set_trigger_data(led_cdev, trigger_data);
+
+	INIT_DELAYED_WORK(&trigger_data->dwork, ledtrig_tty_work);
+	trigger_data->led_cdev = led_cdev;
+	init_completion(&trigger_data->sysfs);
+
+	schedule_delayed_work(&trigger_data->dwork, 0);
+
+	return 0;
+}
+
+static void ledtrig_tty_deactivate(struct led_classdev *led_cdev)
+{
+	struct ledtrig_tty_data *trigger_data = led_get_trigger_data(led_cdev);
+
+	cancel_delayed_work_sync(&trigger_data->dwork);
+
+	kfree(trigger_data->ttyname);
+	tty_kref_put(trigger_data->tty);
+	trigger_data->tty = NULL;
+
+	kfree(trigger_data);
+}
+
+static struct led_trigger ledtrig_tty = {
+	.name = "tty",
+	.activate = ledtrig_tty_activate,
+	.deactivate = ledtrig_tty_deactivate,
+	.groups = ledtrig_tty_groups,
+};
+module_led_trigger(ledtrig_tty);
+
+MODULE_AUTHOR("Uwe Kleine-König <u.kleine-koenig@pengutronix.de>");
+MODULE_DESCRIPTION("UART LED trigger");
+MODULE_LICENSE("GPL v2");