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, 242 insertions, 0 deletions

diff --git a/drivers/rtc/rtc-ds1390.c b/drivers/rtc/rtc-ds1390.c
new file mode 100644
index 000000000..f7afd6bde
--- /dev/null
+++ b/drivers/rtc/rtc-ds1390.c
@@ -0,0 +1,242 @@
+// SPDX-License-Identifier: GPL-2.0-only
+/*
+ * rtc-ds1390.c -- driver for the Dallas/Maxim DS1390/93/94 SPI RTC
+ *
+ * Copyright (C) 2008 Mercury IMC Ltd
+ * Written by Mark Jackson <mpfj@mimc.co.uk>
+ *
+ * NOTE: Currently this driver only supports the bare minimum for read
+ * and write the RTC. The extra features provided by the chip family
+ * (alarms, trickle charger, different control registers) are unavailable.
+ */
+
+#include <linux/init.h>
+#include <linux/module.h>
+#include <linux/platform_device.h>
+#include <linux/rtc.h>
+#include <linux/spi/spi.h>
+#include <linux/bcd.h>
+#include <linux/slab.h>
+#include <linux/of.h>
+
+#define DS1390_REG_100THS		0x00
+#define DS1390_REG_SECONDS		0x01
+#define DS1390_REG_MINUTES		0x02
+#define DS1390_REG_HOURS		0x03
+#define DS1390_REG_DAY			0x04
+#define DS1390_REG_DATE			0x05
+#define DS1390_REG_MONTH_CENT		0x06
+#define DS1390_REG_YEAR			0x07
+
+#define DS1390_REG_ALARM_100THS		0x08
+#define DS1390_REG_ALARM_SECONDS	0x09
+#define DS1390_REG_ALARM_MINUTES	0x0A
+#define DS1390_REG_ALARM_HOURS		0x0B
+#define DS1390_REG_ALARM_DAY_DATE	0x0C
+
+#define DS1390_REG_CONTROL		0x0D
+#define DS1390_REG_STATUS		0x0E
+#define DS1390_REG_TRICKLE		0x0F
+
+#define DS1390_TRICKLE_CHARGER_ENABLE	0xA0
+#define DS1390_TRICKLE_CHARGER_250_OHM	0x01
+#define DS1390_TRICKLE_CHARGER_2K_OHM	0x02
+#define DS1390_TRICKLE_CHARGER_4K_OHM	0x03
+#define DS1390_TRICKLE_CHARGER_NO_DIODE	0x04
+#define DS1390_TRICKLE_CHARGER_DIODE	0x08
+
+struct ds1390 {
+	struct rtc_device *rtc;
+	u8 txrx_buf[9];	/* cmd + 8 registers */
+};
+
+static void ds1390_set_reg(struct device *dev, unsigned char address,
+			   unsigned char data)
+{
+	struct spi_device *spi = to_spi_device(dev);
+	unsigned char buf[2];
+
+	/* MSB must be '1' to write */
+	buf[0] = address | 0x80;
+	buf[1] = data;
+
+	spi_write(spi, buf, 2);
+}
+
+static int ds1390_get_reg(struct device *dev, unsigned char address,
+				unsigned char *data)
+{
+	struct spi_device *spi = to_spi_device(dev);
+	struct ds1390 *chip = dev_get_drvdata(dev);
+	int status;
+
+	if (!data)
+		return -EINVAL;
+
+	/* Clear MSB to indicate read */
+	chip->txrx_buf[0] = address & 0x7f;
+	/* do the i/o */
+	status = spi_write_then_read(spi, chip->txrx_buf, 1, chip->txrx_buf, 1);
+	if (status != 0)
+		return status;
+
+	*data = chip->txrx_buf[0];
+
+	return 0;
+}
+
+static void ds1390_trickle_of_init(struct spi_device *spi)
+{
+	u32 ohms = 0;
+	u8 value;
+
+	if (of_property_read_u32(spi->dev.of_node, "trickle-resistor-ohms",
+				 &ohms))
+		goto out;
+
+	/* Enable charger */
+	value = DS1390_TRICKLE_CHARGER_ENABLE;
+	if (of_property_read_bool(spi->dev.of_node, "trickle-diode-disable"))
+		value |= DS1390_TRICKLE_CHARGER_NO_DIODE;
+	else
+		value |= DS1390_TRICKLE_CHARGER_DIODE;
+
+	/* Resistor select */
+	switch (ohms) {
+	case 250:
+		value |= DS1390_TRICKLE_CHARGER_250_OHM;
+		break;
+	case 2000:
+		value |= DS1390_TRICKLE_CHARGER_2K_OHM;
+		break;
+	case 4000:
+		value |= DS1390_TRICKLE_CHARGER_4K_OHM;
+		break;
+	default:
+		dev_warn(&spi->dev,
+			 "Unsupported ohm value %02ux in dt\n", ohms);
+		return;
+	}
+
+	ds1390_set_reg(&spi->dev, DS1390_REG_TRICKLE, value);
+
+out:
+	return;
+}
+
+static int ds1390_read_time(struct device *dev, struct rtc_time *dt)
+{
+	struct spi_device *spi = to_spi_device(dev);
+	struct ds1390 *chip = dev_get_drvdata(dev);
+	int status;
+
+	/* build the message */
+	chip->txrx_buf[0] = DS1390_REG_SECONDS;
+
+	/* do the i/o */
+	status = spi_write_then_read(spi, chip->txrx_buf, 1, chip->txrx_buf, 7);
+	if (status != 0)
+		return status;
+
+	/* The chip sends data in this order:
+	 * Seconds, Minutes, Hours, Day, Date, Month / Century, Year */
+	dt->tm_sec	= bcd2bin(chip->txrx_buf[0]);
+	dt->tm_min	= bcd2bin(chip->txrx_buf[1]);
+	dt->tm_hour	= bcd2bin(chip->txrx_buf[2]);
+	dt->tm_wday	= bcd2bin(chip->txrx_buf[3]);
+	dt->tm_mday	= bcd2bin(chip->txrx_buf[4]);
+	/* mask off century bit */
+	dt->tm_mon	= bcd2bin(chip->txrx_buf[5] & 0x7f) - 1;
+	/* adjust for century bit */
+	dt->tm_year = bcd2bin(chip->txrx_buf[6]) + ((chip->txrx_buf[5] & 0x80) ? 100 : 0);
+
+	return 0;
+}
+
+static int ds1390_set_time(struct device *dev, struct rtc_time *dt)
+{
+	struct spi_device *spi = to_spi_device(dev);
+	struct ds1390 *chip = dev_get_drvdata(dev);
+
+	/* build the message */
+	chip->txrx_buf[0] = DS1390_REG_SECONDS | 0x80;
+	chip->txrx_buf[1] = bin2bcd(dt->tm_sec);
+	chip->txrx_buf[2] = bin2bcd(dt->tm_min);
+	chip->txrx_buf[3] = bin2bcd(dt->tm_hour);
+	chip->txrx_buf[4] = bin2bcd(dt->tm_wday);
+	chip->txrx_buf[5] = bin2bcd(dt->tm_mday);
+	chip->txrx_buf[6] = bin2bcd(dt->tm_mon + 1) |
+				((dt->tm_year > 99) ? 0x80 : 0x00);
+	chip->txrx_buf[7] = bin2bcd(dt->tm_year % 100);
+
+	/* do the i/o */
+	return spi_write_then_read(spi, chip->txrx_buf, 8, NULL, 0);
+}
+
+static const struct rtc_class_ops ds1390_rtc_ops = {
+	.read_time	= ds1390_read_time,
+	.set_time	= ds1390_set_time,
+};
+
+static int ds1390_probe(struct spi_device *spi)
+{
+	unsigned char tmp;
+	struct ds1390 *chip;
+	int res;
+
+	spi->mode = SPI_MODE_3;
+	spi->bits_per_word = 8;
+	spi_setup(spi);
+
+	chip = devm_kzalloc(&spi->dev, sizeof(*chip), GFP_KERNEL);
+	if (!chip)
+		return -ENOMEM;
+
+	spi_set_drvdata(spi, chip);
+
+	res = ds1390_get_reg(&spi->dev, DS1390_REG_SECONDS, &tmp);
+	if (res != 0) {
+		dev_err(&spi->dev, "unable to read device\n");
+		return res;
+	}
+
+	if (spi->dev.of_node)
+		ds1390_trickle_of_init(spi);
+
+	chip->rtc = devm_rtc_device_register(&spi->dev, "ds1390",
+					&ds1390_rtc_ops, THIS_MODULE);
+	if (IS_ERR(chip->rtc)) {
+		dev_err(&spi->dev, "unable to register device\n");
+		res = PTR_ERR(chip->rtc);
+	}
+
+	return res;
+}
+
+static const struct of_device_id ds1390_of_match[] __maybe_unused = {
+	{ .compatible = "dallas,ds1390" },
+	{}
+};
+MODULE_DEVICE_TABLE(of, ds1390_of_match);
+
+static const struct spi_device_id ds1390_spi_ids[] = {
+	{ .name = "ds1390" },
+	{}
+};
+MODULE_DEVICE_TABLE(spi, ds1390_spi_ids);
+
+static struct spi_driver ds1390_driver = {
+	.driver = {
+		.name	= "rtc-ds1390",
+		.of_match_table = of_match_ptr(ds1390_of_match),
+	},
+	.probe	= ds1390_probe,
+	.id_table = ds1390_spi_ids,
+};
+
+module_spi_driver(ds1390_driver);
+
+MODULE_DESCRIPTION("Dallas/Maxim DS1390/93/94 SPI RTC driver");
+MODULE_AUTHOR("Mark Jackson <mpfj@mimc.co.uk>");
+MODULE_LICENSE("GPL");
+MODULE_ALIAS("spi:rtc-ds1390");