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, 333 insertions, 0 deletions

diff --git a/drivers/hwmon/max127.c b/drivers/hwmon/max127.c
new file mode 100644
index 000000000..b294e86d5
--- /dev/null
+++ b/drivers/hwmon/max127.c
@@ -0,0 +1,333 @@
+// SPDX-License-Identifier: GPL-2.0+
+/*
+ * Hardware monitoring driver for MAX127.
+ *
+ * Copyright (c) 2020 Facebook Inc.
+ */
+
+#include <linux/err.h>
+#include <linux/hwmon.h>
+#include <linux/i2c.h>
+#include <linux/init.h>
+#include <linux/module.h>
+
+/*
+ * MAX127 Control Byte. Refer to MAX127 datasheet, Table 1 "Control-Byte
+ * Format" for details.
+ */
+#define MAX127_CTRL_START	BIT(7)
+#define MAX127_CTRL_SEL_SHIFT	4
+#define MAX127_CTRL_RNG		BIT(3)
+#define MAX127_CTRL_BIP		BIT(2)
+#define MAX127_CTRL_PD1		BIT(1)
+#define MAX127_CTRL_PD0		BIT(0)
+
+#define MAX127_NUM_CHANNELS	8
+#define MAX127_SET_CHANNEL(ch)	(((ch) & 7) << MAX127_CTRL_SEL_SHIFT)
+
+/*
+ * MAX127 channel input ranges. Refer to MAX127 datasheet, Table 3 "Range
+ * and Polarity Selection" for details.
+ */
+#define MAX127_FULL_RANGE	10000	/* 10V */
+#define MAX127_HALF_RANGE	5000	/* 5V */
+
+/*
+ * MAX127 returns 2 bytes at read:
+ *   - the first byte contains data[11:4].
+ *   - the second byte contains data[3:0] (MSB) and 4 dummy 0s (LSB).
+ * Refer to MAX127 datasheet, "Read a Conversion (Read Cycle)" section
+ * for details.
+ */
+#define MAX127_DATA_LEN		2
+#define MAX127_DATA_SHIFT	4
+
+#define MAX127_SIGN_BIT		BIT(11)
+
+struct max127_data {
+	struct i2c_client *client;
+	u8 ctrl_byte[MAX127_NUM_CHANNELS];
+};
+
+static int max127_select_channel(struct i2c_client *client, u8 ctrl_byte)
+{
+	int status;
+	struct i2c_msg msg = {
+		.addr = client->addr,
+		.flags = 0,
+		.len = sizeof(ctrl_byte),
+		.buf = &ctrl_byte,
+	};
+
+	status = i2c_transfer(client->adapter, &msg, 1);
+	if (status < 0)
+		return status;
+	if (status != 1)
+		return -EIO;
+
+	return 0;
+}
+
+static int max127_read_channel(struct i2c_client *client, long *val)
+{
+	int status;
+	u8 i2c_data[MAX127_DATA_LEN];
+	struct i2c_msg msg = {
+		.addr = client->addr,
+		.flags = I2C_M_RD,
+		.len = sizeof(i2c_data),
+		.buf = i2c_data,
+	};
+
+	status = i2c_transfer(client->adapter, &msg, 1);
+	if (status < 0)
+		return status;
+	if (status != 1)
+		return -EIO;
+
+	*val = (i2c_data[1] >> MAX127_DATA_SHIFT) |
+		((u16)i2c_data[0] << MAX127_DATA_SHIFT);
+	return 0;
+}
+
+static long max127_process_raw(u8 ctrl_byte, long raw)
+{
+	long scale, weight;
+
+	/*
+	 * MAX127's data coding is binary in unipolar mode with 1 LSB =
+	 * (Full-Scale/4096) and two’s complement binary in bipolar mode
+	 * with 1 LSB = [(2 x |FS|)/4096].
+	 * Refer to MAX127 datasheet, "Transfer Function" section for
+	 * details.
+	 */
+	scale = (ctrl_byte & MAX127_CTRL_RNG) ? MAX127_FULL_RANGE :
+						MAX127_HALF_RANGE;
+	if (ctrl_byte & MAX127_CTRL_BIP) {
+		weight = (raw & MAX127_SIGN_BIT);
+		raw &= ~MAX127_SIGN_BIT;
+		raw -= weight;
+		raw *= 2;
+	}
+
+	return raw * scale / 4096;
+}
+
+static int max127_read_input(struct max127_data *data, int channel, long *val)
+{
+	long raw;
+	int status;
+	struct i2c_client *client = data->client;
+	u8 ctrl_byte = data->ctrl_byte[channel];
+
+	status = max127_select_channel(client, ctrl_byte);
+	if (status)
+		return status;
+
+	status = max127_read_channel(client, &raw);
+	if (status)
+		return status;
+
+	*val = max127_process_raw(ctrl_byte, raw);
+	return 0;
+}
+
+static int max127_read_min(struct max127_data *data, int channel, long *val)
+{
+	u8 rng_bip = (data->ctrl_byte[channel] >> 2) & 3;
+	static const int min_input_map[4] = {
+		0,			/* RNG=0, BIP=0 */
+		-MAX127_HALF_RANGE,	/* RNG=0, BIP=1 */
+		0,			/* RNG=1, BIP=0 */
+		-MAX127_FULL_RANGE,	/* RNG=1, BIP=1 */
+	};
+
+	*val = min_input_map[rng_bip];
+	return 0;
+}
+
+static int max127_read_max(struct max127_data *data, int channel, long *val)
+{
+	u8 rng_bip = (data->ctrl_byte[channel] >> 2) & 3;
+	static const int max_input_map[4] = {
+		MAX127_HALF_RANGE,	/* RNG=0, BIP=0 */
+		MAX127_HALF_RANGE,	/* RNG=0, BIP=1 */
+		MAX127_FULL_RANGE,	/* RNG=1, BIP=0 */
+		MAX127_FULL_RANGE,	/* RNG=1, BIP=1 */
+	};
+
+	*val = max_input_map[rng_bip];
+	return 0;
+}
+
+static int max127_write_min(struct max127_data *data, int channel, long val)
+{
+	u8 ctrl;
+
+	ctrl = data->ctrl_byte[channel];
+	if (val <= -MAX127_FULL_RANGE) {
+		ctrl |= (MAX127_CTRL_RNG | MAX127_CTRL_BIP);
+	} else if (val < 0) {
+		ctrl |= MAX127_CTRL_BIP;
+		ctrl &= ~MAX127_CTRL_RNG;
+	} else {
+		ctrl &= ~MAX127_CTRL_BIP;
+	}
+	data->ctrl_byte[channel] = ctrl;
+	return 0;
+}
+
+static int max127_write_max(struct max127_data *data, int channel, long val)
+{
+	if (val >= MAX127_FULL_RANGE)
+		data->ctrl_byte[channel] |= MAX127_CTRL_RNG;
+	else
+		data->ctrl_byte[channel] &= ~MAX127_CTRL_RNG;
+	return 0;
+}
+
+static umode_t max127_is_visible(const void *_data,
+				 enum hwmon_sensor_types type,
+				 u32 attr, int channel)
+{
+	if (type == hwmon_in) {
+		switch (attr) {
+		case hwmon_in_input:
+			return 0444;
+
+		case hwmon_in_min:
+		case hwmon_in_max:
+			return 0644;
+
+		default:
+			break;
+		}
+	}
+
+	return 0;
+}
+
+static int max127_read(struct device *dev, enum hwmon_sensor_types type,
+			u32 attr, int channel, long *val)
+{
+	int status;
+	struct max127_data *data = dev_get_drvdata(dev);
+
+	if (type != hwmon_in)
+		return -EOPNOTSUPP;
+
+	switch (attr) {
+	case hwmon_in_input:
+		status = max127_read_input(data, channel, val);
+		break;
+
+	case hwmon_in_min:
+		status = max127_read_min(data, channel, val);
+		break;
+
+	case hwmon_in_max:
+		status = max127_read_max(data, channel, val);
+		break;
+
+	default:
+		status = -EOPNOTSUPP;
+		break;
+	}
+
+	return status;
+}
+
+static int max127_write(struct device *dev, enum hwmon_sensor_types type,
+			u32 attr, int channel, long val)
+{
+	int status;
+	struct max127_data *data = dev_get_drvdata(dev);
+
+	if (type != hwmon_in)
+		return -EOPNOTSUPP;
+
+	switch (attr) {
+	case hwmon_in_min:
+		status = max127_write_min(data, channel, val);
+		break;
+
+	case hwmon_in_max:
+		status = max127_write_max(data, channel, val);
+		break;
+
+	default:
+		status = -EOPNOTSUPP;
+		break;
+	}
+
+	return status;
+}
+
+static const struct hwmon_ops max127_hwmon_ops = {
+	.is_visible = max127_is_visible,
+	.read = max127_read,
+	.write = max127_write,
+};
+
+static const struct hwmon_channel_info * const max127_info[] = {
+	HWMON_CHANNEL_INFO(in,
+			   HWMON_I_INPUT | HWMON_I_MIN | HWMON_I_MAX,
+			   HWMON_I_INPUT | HWMON_I_MIN | HWMON_I_MAX,
+			   HWMON_I_INPUT | HWMON_I_MIN | HWMON_I_MAX,
+			   HWMON_I_INPUT | HWMON_I_MIN | HWMON_I_MAX,
+			   HWMON_I_INPUT | HWMON_I_MIN | HWMON_I_MAX,
+			   HWMON_I_INPUT | HWMON_I_MIN | HWMON_I_MAX,
+			   HWMON_I_INPUT | HWMON_I_MIN | HWMON_I_MAX,
+			   HWMON_I_INPUT | HWMON_I_MIN | HWMON_I_MAX),
+	NULL,
+};
+
+static const struct hwmon_chip_info max127_chip_info = {
+	.ops = &max127_hwmon_ops,
+	.info = max127_info,
+};
+
+static int max127_probe(struct i2c_client *client)
+{
+	int i;
+	struct device *hwmon_dev;
+	struct max127_data *data;
+	struct device *dev = &client->dev;
+
+	data = devm_kzalloc(dev, sizeof(*data), GFP_KERNEL);
+	if (!data)
+		return -ENOMEM;
+
+	data->client = client;
+	for (i = 0; i < ARRAY_SIZE(data->ctrl_byte); i++)
+		data->ctrl_byte[i] = (MAX127_CTRL_START |
+				      MAX127_SET_CHANNEL(i));
+
+	hwmon_dev = devm_hwmon_device_register_with_info(dev, client->name,
+							 data,
+							 &max127_chip_info,
+							 NULL);
+
+	return PTR_ERR_OR_ZERO(hwmon_dev);
+}
+
+static const struct i2c_device_id max127_id[] = {
+	{ .name = "max127" },
+	{ }
+};
+MODULE_DEVICE_TABLE(i2c, max127_id);
+
+static struct i2c_driver max127_driver = {
+	.driver = {
+		.name	= "max127",
+	},
+	.probe		= max127_probe,
+	.id_table	= max127_id,
+};
+
+module_i2c_driver(max127_driver);
+
+MODULE_LICENSE("GPL");
+MODULE_AUTHOR("Mike Choi <mikechoi@fb.com>");
+MODULE_AUTHOR("Tao Ren <rentao.bupt@gmail.com>");
+MODULE_DESCRIPTION("MAX127 Hardware Monitoring driver");