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, 135 insertions, 0 deletions

diff --git a/drivers/leds/leds-spi-byte.c b/drivers/leds/leds-spi-byte.c
new file mode 100644
index 000000000..0217557aa
--- /dev/null
+++ b/drivers/leds/leds-spi-byte.c
@@ -0,0 +1,135 @@
+// SPDX-License-Identifier: GPL-2.0
+// Copyright (c) 2019 Christian Mauderer <oss@c-mauderer.de>
+
+/*
+ * The driver supports controllers with a very simple SPI protocol:
+ * - one LED is controlled by a single byte on MOSI
+ * - the value of the byte gives the brightness between two values (lowest to
+ *   highest)
+ * - no return value is necessary (no MISO signal)
+ *
+ * The value for minimum and maximum brightness depends on the device
+ * (compatible string).
+ *
+ * Supported devices:
+ * - "ubnt,acb-spi-led": Microcontroller (SONiX 8F26E611LA) based device used
+ *   for example in Ubiquiti airCube ISP. Reverse engineered protocol for this
+ *   controller:
+ *   * Higher two bits set a mode. Lower six bits are a parameter.
+ *   * Mode: 00 -> set brightness between 0x00 (min) and 0x3F (max)
+ *   * Mode: 01 -> pulsing pattern (min -> max -> min) with an interval. From
+ *     some tests, the period is about (50ms + 102ms * parameter). There is a
+ *     slightly different pattern starting from 0x10 (longer gap between the
+ *     pulses) but the time still follows that calculation.
+ *   * Mode: 10 -> same as 01 but with only a ramp from min to max. Again a
+ *     slight jump in the pattern at 0x10.
+ *   * Mode: 11 -> blinking (off -> 25% -> off -> 25% -> ...) with a period of
+ *     (105ms * parameter)
+ *   NOTE: This driver currently only supports mode 00.
+ */
+
+#include <linux/leds.h>
+#include <linux/module.h>
+#include <linux/mutex.h>
+#include <linux/property.h>
+#include <linux/spi/spi.h>
+#include <uapi/linux/uleds.h>
+
+struct spi_byte_chipdef {
+	/* SPI byte that will be send to switch the LED off */
+	u8	off_value;
+	/* SPI byte that will be send to switch the LED to maximum brightness */
+	u8	max_value;
+};
+
+struct spi_byte_led {
+	struct led_classdev		ldev;
+	struct spi_device		*spi;
+	char				name[LED_MAX_NAME_SIZE];
+	struct mutex			mutex;
+	const struct spi_byte_chipdef	*cdef;
+};
+
+static const struct spi_byte_chipdef ubnt_acb_spi_led_cdef = {
+	.off_value = 0x0,
+	.max_value = 0x3F,
+};
+
+static int spi_byte_brightness_set_blocking(struct led_classdev *dev,
+					    enum led_brightness brightness)
+{
+	struct spi_byte_led *led = container_of(dev, struct spi_byte_led, ldev);
+	u8 value;
+	int ret;
+
+	value = (u8) brightness + led->cdef->off_value;
+
+	mutex_lock(&led->mutex);
+	ret = spi_write(led->spi, &value, sizeof(value));
+	mutex_unlock(&led->mutex);
+
+	return ret;
+}
+
+static int spi_byte_probe(struct spi_device *spi)
+{
+	struct fwnode_handle *child __free(fwnode_handle) = NULL;
+	struct device *dev = &spi->dev;
+	struct spi_byte_led *led;
+	struct led_init_data init_data = {};
+	enum led_default_state state;
+	int ret;
+
+	if (device_get_child_node_count(dev) != 1) {
+		dev_err(dev, "Device must have exactly one LED sub-node.");
+		return -EINVAL;
+	}
+
+	led = devm_kzalloc(dev, sizeof(*led), GFP_KERNEL);
+	if (!led)
+		return -ENOMEM;
+
+	ret = devm_mutex_init(dev, &led->mutex);
+	if (ret)
+		return ret;
+
+	led->spi = spi;
+	led->cdef = device_get_match_data(dev);
+	led->ldev.brightness = LED_OFF;
+	led->ldev.max_brightness = led->cdef->max_value - led->cdef->off_value;
+	led->ldev.brightness_set_blocking = spi_byte_brightness_set_blocking;
+
+	child = device_get_next_child_node(dev, NULL);
+
+	state = led_init_default_state_get(child);
+	if (state == LEDS_DEFSTATE_ON)
+		led->ldev.brightness = led->ldev.max_brightness;
+	spi_byte_brightness_set_blocking(&led->ldev,
+					 led->ldev.brightness);
+
+	init_data.fwnode = child;
+	init_data.devicename = "leds-spi-byte";
+	init_data.default_label = ":";
+
+	return devm_led_classdev_register_ext(dev, &led->ldev, &init_data);
+}
+
+static const struct of_device_id spi_byte_dt_ids[] = {
+	{ .compatible = "ubnt,acb-spi-led", .data = &ubnt_acb_spi_led_cdef },
+	{}
+};
+MODULE_DEVICE_TABLE(of, spi_byte_dt_ids);
+
+static struct spi_driver spi_byte_driver = {
+	.probe		= spi_byte_probe,
+	.driver = {
+		.name		= KBUILD_MODNAME,
+		.of_match_table	= spi_byte_dt_ids,
+	},
+};
+module_spi_driver(spi_byte_driver);
+
+MODULE_AUTHOR("Christian Mauderer <oss@c-mauderer.de>");
+MODULE_DESCRIPTION("single byte SPI LED driver");
+MODULE_LICENSE("GPL v2");
+MODULE_ALIAS("spi:leds-spi-byte");