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, 142 insertions, 0 deletions

diff --git a/drivers/leds/trigger/ledtrig-gpio.c b/drivers/leds/trigger/ledtrig-gpio.c
new file mode 100644
index 000000000..3b3e6869e
--- /dev/null
+++ b/drivers/leds/trigger/ledtrig-gpio.c
@@ -0,0 +1,142 @@
+// SPDX-License-Identifier: GPL-2.0-only
+/*
+ * ledtrig-gio.c - LED Trigger Based on GPIO events
+ *
+ * Copyright 2009 Felipe Balbi <me@felipebalbi.com>
+ * Copyright 2023 Linus Walleij <linus.walleij@linaro.org>
+ */
+
+#include <linux/module.h>
+#include <linux/kernel.h>
+#include <linux/init.h>
+#include <linux/gpio/consumer.h>
+#include <linux/interrupt.h>
+#include <linux/leds.h>
+#include <linux/slab.h>
+#include "../leds.h"
+
+struct gpio_trig_data {
+	struct led_classdev *led;
+	unsigned desired_brightness;	/* desired brightness when led is on */
+	struct gpio_desc *gpiod;	/* gpio that triggers the led */
+};
+
+static irqreturn_t gpio_trig_irq(int irq, void *_led)
+{
+	struct led_classdev *led = _led;
+	struct gpio_trig_data *gpio_data = led_get_trigger_data(led);
+	int tmp;
+
+	tmp = gpiod_get_value_cansleep(gpio_data->gpiod);
+	if (tmp) {
+		if (gpio_data->desired_brightness)
+			led_set_brightness_nosleep(gpio_data->led,
+					   gpio_data->desired_brightness);
+		else
+			led_set_brightness_nosleep(gpio_data->led, LED_FULL);
+	} else {
+		led_set_brightness_nosleep(gpio_data->led, LED_OFF);
+	}
+
+	return IRQ_HANDLED;
+}
+
+static ssize_t desired_brightness_show(struct device *dev,
+		struct device_attribute *attr, char *buf)
+{
+	struct gpio_trig_data *gpio_data = led_trigger_get_drvdata(dev);
+
+	return sysfs_emit(buf, "%u\n", gpio_data->desired_brightness);
+}
+
+static ssize_t desired_brightness_store(struct device *dev,
+		struct device_attribute *attr, const char *buf, size_t n)
+{
+	struct gpio_trig_data *gpio_data = led_trigger_get_drvdata(dev);
+	u8 desired_brightness;
+	int ret;
+
+	ret = kstrtou8(buf, 10, &desired_brightness);
+	if (ret)
+		return ret;
+
+	gpio_data->desired_brightness = desired_brightness;
+
+	return n;
+}
+static DEVICE_ATTR_RW(desired_brightness);
+
+static struct attribute *gpio_trig_attrs[] = {
+	&dev_attr_desired_brightness.attr,
+	NULL
+};
+ATTRIBUTE_GROUPS(gpio_trig);
+
+static int gpio_trig_activate(struct led_classdev *led)
+{
+	struct gpio_trig_data *gpio_data;
+	struct device *dev = led->dev;
+	int ret;
+
+	gpio_data = kzalloc_obj(*gpio_data);
+	if (!gpio_data)
+		return -ENOMEM;
+
+	/*
+	 * The generic property "trigger-sources" is followed,
+	 * and we hope that this is a GPIO.
+	 */
+	gpio_data->gpiod = gpiod_get_optional(dev, "trigger-sources",
+					      GPIOD_IN | GPIOD_FLAGS_BIT_NONEXCLUSIVE);
+	if (IS_ERR(gpio_data->gpiod)) {
+		ret = PTR_ERR(gpio_data->gpiod);
+		kfree(gpio_data);
+		return ret;
+	}
+	if (!gpio_data->gpiod) {
+		dev_err(dev, "no valid GPIO for the trigger\n");
+		kfree(gpio_data);
+		return -EINVAL;
+	}
+
+	gpiod_set_consumer_name(gpio_data->gpiod, "led-trigger");
+
+	gpio_data->led = led;
+	led_set_trigger_data(led, gpio_data);
+
+	ret = request_threaded_irq(gpiod_to_irq(gpio_data->gpiod), NULL, gpio_trig_irq,
+			IRQF_ONESHOT | IRQF_SHARED | IRQF_TRIGGER_RISING
+			| IRQF_TRIGGER_FALLING, "ledtrig-gpio", led);
+	if (ret) {
+		dev_err(dev, "request_irq failed with error %d\n", ret);
+		gpiod_put(gpio_data->gpiod);
+		kfree(gpio_data);
+		return ret;
+	}
+
+	/* Finally update the LED to initial status */
+	gpio_trig_irq(0, led);
+
+	return 0;
+}
+
+static void gpio_trig_deactivate(struct led_classdev *led)
+{
+	struct gpio_trig_data *gpio_data = led_get_trigger_data(led);
+
+	free_irq(gpiod_to_irq(gpio_data->gpiod), led);
+	gpiod_put(gpio_data->gpiod);
+	kfree(gpio_data);
+}
+
+static struct led_trigger gpio_led_trigger = {
+	.name		= "gpio",
+	.activate	= gpio_trig_activate,
+	.deactivate	= gpio_trig_deactivate,
+	.groups		= gpio_trig_groups,
+};
+module_led_trigger(gpio_led_trigger);
+
+MODULE_AUTHOR("Felipe Balbi <me@felipebalbi.com>");
+MODULE_DESCRIPTION("GPIO LED trigger");
+MODULE_LICENSE("GPL v2");