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, 317 insertions, 0 deletions

diff --git a/drivers/rtc/rtc-pcf8583.c b/drivers/rtc/rtc-pcf8583.c
new file mode 100644
index 000000000..df5e20cbc
--- /dev/null
+++ b/drivers/rtc/rtc-pcf8583.c
@@ -0,0 +1,317 @@
+// SPDX-License-Identifier: GPL-2.0-only
+/*
+ *  drivers/rtc/rtc-pcf8583.c
+ *
+ *  Copyright (C) 2000 Russell King
+ *  Copyright (C) 2008 Wolfram Sang & Juergen Beisert, Pengutronix
+ *
+ *  Driver for PCF8583 RTC & RAM chip
+ *
+ *  Converted to the generic RTC susbsystem by G. Liakhovetski (2006)
+ */
+#include <linux/module.h>
+#include <linux/i2c.h>
+#include <linux/slab.h>
+#include <linux/rtc.h>
+#include <linux/init.h>
+#include <linux/err.h>
+#include <linux/errno.h>
+#include <linux/bcd.h>
+
+struct rtc_mem {
+	unsigned int	loc;
+	unsigned int	nr;
+	unsigned char	*data;
+};
+
+struct pcf8583 {
+	struct rtc_device *rtc;
+	unsigned char ctrl;
+};
+
+#define CTRL_STOP	0x80
+#define CTRL_HOLD	0x40
+#define CTRL_32KHZ	0x00
+#define CTRL_MASK	0x08
+#define CTRL_ALARMEN	0x04
+#define CTRL_ALARM	0x02
+#define CTRL_TIMER	0x01
+
+
+static struct i2c_driver pcf8583_driver;
+
+#define get_ctrl(x)    ((struct pcf8583 *)i2c_get_clientdata(x))->ctrl
+#define set_ctrl(x, v) get_ctrl(x) = v
+
+#define CMOS_YEAR	(64 + 128)
+#define CMOS_CHECKSUM	(63)
+
+static int pcf8583_get_datetime(struct i2c_client *client, struct rtc_time *dt)
+{
+	unsigned char buf[8], addr[1] = { 1 };
+	struct i2c_msg msgs[2] = {
+		{
+			.addr = client->addr,
+			.flags = 0,
+			.len = 1,
+			.buf = addr,
+		}, {
+			.addr = client->addr,
+			.flags = I2C_M_RD,
+			.len = 6,
+			.buf = buf,
+		}
+	};
+	int ret;
+
+	memset(buf, 0, sizeof(buf));
+
+	ret = i2c_transfer(client->adapter, msgs, 2);
+	if (ret == 2) {
+		dt->tm_year = buf[4] >> 6;
+		dt->tm_wday = buf[5] >> 5;
+
+		buf[4] &= 0x3f;
+		buf[5] &= 0x1f;
+
+		dt->tm_sec = bcd2bin(buf[1]);
+		dt->tm_min = bcd2bin(buf[2]);
+		dt->tm_hour = bcd2bin(buf[3]);
+		dt->tm_mday = bcd2bin(buf[4]);
+		dt->tm_mon = bcd2bin(buf[5]) - 1;
+	}
+
+	return ret == 2 ? 0 : -EIO;
+}
+
+static int pcf8583_set_datetime(struct i2c_client *client, struct rtc_time *dt, int datetoo)
+{
+	unsigned char buf[8];
+	int ret, len = 6;
+
+	buf[0] = 0;
+	buf[1] = get_ctrl(client) | 0x80;
+	buf[2] = 0;
+	buf[3] = bin2bcd(dt->tm_sec);
+	buf[4] = bin2bcd(dt->tm_min);
+	buf[5] = bin2bcd(dt->tm_hour);
+
+	if (datetoo) {
+		len = 8;
+		buf[6] = bin2bcd(dt->tm_mday) | (dt->tm_year << 6);
+		buf[7] = bin2bcd(dt->tm_mon + 1)  | (dt->tm_wday << 5);
+	}
+
+	ret = i2c_master_send(client, (char *)buf, len);
+	if (ret != len)
+		return -EIO;
+
+	buf[1] = get_ctrl(client);
+	ret = i2c_master_send(client, (char *)buf, 2);
+
+	return ret == 2 ? 0 : -EIO;
+}
+
+static int pcf8583_get_ctrl(struct i2c_client *client, unsigned char *ctrl)
+{
+	*ctrl = get_ctrl(client);
+	return 0;
+}
+
+static int pcf8583_set_ctrl(struct i2c_client *client, unsigned char *ctrl)
+{
+	unsigned char buf[2];
+
+	buf[0] = 0;
+	buf[1] = *ctrl;
+	set_ctrl(client, *ctrl);
+
+	return i2c_master_send(client, (char *)buf, 2);
+}
+
+static int pcf8583_read_mem(struct i2c_client *client, struct rtc_mem *mem)
+{
+	unsigned char addr[1];
+	struct i2c_msg msgs[2] = {
+		{
+			.addr = client->addr,
+			.flags = 0,
+			.len = 1,
+			.buf = addr,
+		}, {
+			.addr = client->addr,
+			.flags = I2C_M_RD,
+			.len = mem->nr,
+			.buf = mem->data,
+		}
+	};
+
+	if (mem->loc < 8)
+		return -EINVAL;
+
+	addr[0] = mem->loc;
+
+	return i2c_transfer(client->adapter, msgs, 2) == 2 ? 0 : -EIO;
+}
+
+static int pcf8583_write_mem(struct i2c_client *client, struct rtc_mem *mem)
+{
+	unsigned char buf[9];
+	int ret;
+
+	if (mem->loc < 8 || mem->nr > 8)
+		return -EINVAL;
+
+	buf[0] = mem->loc;
+	memcpy(buf + 1, mem->data, mem->nr);
+
+	ret = i2c_master_send(client, buf, mem->nr + 1);
+	return ret == mem->nr + 1 ? 0 : -EIO;
+}
+
+static int pcf8583_rtc_read_time(struct device *dev, struct rtc_time *tm)
+{
+	struct i2c_client *client = to_i2c_client(dev);
+	unsigned char ctrl, year[2];
+	struct rtc_mem mem = {
+		.loc = CMOS_YEAR,
+		.nr = sizeof(year),
+		.data = year
+	};
+	int real_year, year_offset, err;
+
+	/*
+	 * Ensure that the RTC is running.
+	 */
+	pcf8583_get_ctrl(client, &ctrl);
+	if (ctrl & (CTRL_STOP | CTRL_HOLD)) {
+		unsigned char new_ctrl = ctrl & ~(CTRL_STOP | CTRL_HOLD);
+
+		dev_warn(dev, "resetting control %02x -> %02x\n",
+			ctrl, new_ctrl);
+
+		err = pcf8583_set_ctrl(client, &new_ctrl);
+		if (err < 0)
+			return err;
+	}
+
+	if (pcf8583_get_datetime(client, tm) ||
+	    pcf8583_read_mem(client, &mem))
+		return -EIO;
+
+	real_year = year[0];
+
+	/*
+	 * The RTC year holds the LSB two bits of the current
+	 * year, which should reflect the LSB two bits of the
+	 * CMOS copy of the year.  Any difference indicates
+	 * that we have to correct the CMOS version.
+	 */
+	year_offset = tm->tm_year - (real_year & 3);
+	if (year_offset < 0)
+		/*
+		 * RTC year wrapped.  Adjust it appropriately.
+		 */
+		year_offset += 4;
+
+	tm->tm_year = (real_year + year_offset + year[1] * 100) - 1900;
+
+	return 0;
+}
+
+static int pcf8583_rtc_set_time(struct device *dev, struct rtc_time *tm)
+{
+	struct i2c_client *client = to_i2c_client(dev);
+	unsigned char year[2], chk;
+	struct rtc_mem cmos_year  = {
+		.loc = CMOS_YEAR,
+		.nr = sizeof(year),
+		.data = year
+	};
+	struct rtc_mem cmos_check = {
+		.loc = CMOS_CHECKSUM,
+		.nr = 1,
+		.data = &chk
+	};
+	unsigned int proper_year = tm->tm_year + 1900;
+	int ret;
+
+	/*
+	 * The RTC's own 2-bit year must reflect the least
+	 * significant two bits of the CMOS year.
+	 */
+
+	ret = pcf8583_set_datetime(client, tm, 1);
+	if (ret)
+		return ret;
+
+	ret = pcf8583_read_mem(client, &cmos_check);
+	if (ret)
+		return ret;
+
+	ret = pcf8583_read_mem(client, &cmos_year);
+	if (ret)
+		return ret;
+
+	chk -= year[1] + year[0];
+
+	year[1] = proper_year / 100;
+	year[0] = proper_year % 100;
+
+	chk += year[1] + year[0];
+
+	ret = pcf8583_write_mem(client, &cmos_year);
+
+	if (ret)
+		return ret;
+
+	ret = pcf8583_write_mem(client, &cmos_check);
+
+	return ret;
+}
+
+static const struct rtc_class_ops pcf8583_rtc_ops = {
+	.read_time	= pcf8583_rtc_read_time,
+	.set_time	= pcf8583_rtc_set_time,
+};
+
+static int pcf8583_probe(struct i2c_client *client)
+{
+	struct pcf8583 *pcf8583;
+
+	if (!i2c_check_functionality(client->adapter, I2C_FUNC_I2C))
+		return -ENODEV;
+
+	pcf8583 = devm_kzalloc(&client->dev, sizeof(struct pcf8583),
+				GFP_KERNEL);
+	if (!pcf8583)
+		return -ENOMEM;
+
+	i2c_set_clientdata(client, pcf8583);
+
+	pcf8583->rtc = devm_rtc_device_register(&client->dev,
+				pcf8583_driver.driver.name,
+				&pcf8583_rtc_ops, THIS_MODULE);
+
+	return PTR_ERR_OR_ZERO(pcf8583->rtc);
+}
+
+static const struct i2c_device_id pcf8583_id[] = {
+	{ .name = "pcf8583" },
+	{ }
+};
+MODULE_DEVICE_TABLE(i2c, pcf8583_id);
+
+static struct i2c_driver pcf8583_driver = {
+	.driver = {
+		.name	= "pcf8583",
+	},
+	.probe		= pcf8583_probe,
+	.id_table	= pcf8583_id,
+};
+
+module_i2c_driver(pcf8583_driver);
+
+MODULE_AUTHOR("Russell King");
+MODULE_DESCRIPTION("PCF8583 I2C RTC driver");
+MODULE_LICENSE("GPL");