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, 145 insertions, 0 deletions

diff --git a/drivers/rtc/rtc-m41t94.c b/drivers/rtc/rtc-m41t94.c
new file mode 100644
index 000000000..6803b0273
--- /dev/null
+++ b/drivers/rtc/rtc-m41t94.c
@@ -0,0 +1,145 @@
+// SPDX-License-Identifier: GPL-2.0-only
+/*
+ * Driver for ST M41T94 SPI RTC
+ *
+ * Copyright (C) 2008 Kim B. Heino
+ */
+
+#include <linux/module.h>
+#include <linux/kernel.h>
+#include <linux/platform_device.h>
+#include <linux/rtc.h>
+#include <linux/spi/spi.h>
+#include <linux/bcd.h>
+
+#define M41T94_REG_SECONDS	0x01
+#define M41T94_REG_MINUTES	0x02
+#define M41T94_REG_HOURS	0x03
+#define M41T94_REG_WDAY		0x04
+#define M41T94_REG_DAY		0x05
+#define M41T94_REG_MONTH	0x06
+#define M41T94_REG_YEAR		0x07
+#define M41T94_REG_HT		0x0c
+
+#define M41T94_BIT_HALT		0x40
+#define M41T94_BIT_STOP		0x80
+#define M41T94_BIT_CB		0x40
+#define M41T94_BIT_CEB		0x80
+
+static int m41t94_set_time(struct device *dev, struct rtc_time *tm)
+{
+	struct spi_device *spi = to_spi_device(dev);
+	u8 buf[8]; /* write cmd + 7 registers */
+
+	dev_dbg(dev, "%s secs=%d, mins=%d, "
+		"hours=%d, mday=%d, mon=%d, year=%d, wday=%d\n",
+		"write", tm->tm_sec, tm->tm_min,
+		tm->tm_hour, tm->tm_mday,
+		tm->tm_mon, tm->tm_year, tm->tm_wday);
+
+	buf[0] = 0x80 | M41T94_REG_SECONDS; /* write time + date */
+	buf[M41T94_REG_SECONDS] = bin2bcd(tm->tm_sec);
+	buf[M41T94_REG_MINUTES] = bin2bcd(tm->tm_min);
+	buf[M41T94_REG_HOURS]   = bin2bcd(tm->tm_hour);
+	buf[M41T94_REG_WDAY]    = bin2bcd(tm->tm_wday + 1);
+	buf[M41T94_REG_DAY]     = bin2bcd(tm->tm_mday);
+	buf[M41T94_REG_MONTH]   = bin2bcd(tm->tm_mon + 1);
+
+	buf[M41T94_REG_HOURS] |= M41T94_BIT_CEB;
+	if (tm->tm_year >= 100)
+		buf[M41T94_REG_HOURS] |= M41T94_BIT_CB;
+	buf[M41T94_REG_YEAR] = bin2bcd(tm->tm_year % 100);
+
+	return spi_write(spi, buf, 8);
+}
+
+static int m41t94_read_time(struct device *dev, struct rtc_time *tm)
+{
+	struct spi_device *spi = to_spi_device(dev);
+	u8 buf[2];
+	int ret, hour;
+
+	/* clear halt update bit */
+	ret = spi_w8r8(spi, M41T94_REG_HT);
+	if (ret < 0)
+		return ret;
+	if (ret & M41T94_BIT_HALT) {
+		buf[0] = 0x80 | M41T94_REG_HT;
+		buf[1] = ret & ~M41T94_BIT_HALT;
+		spi_write(spi, buf, 2);
+	}
+
+	/* clear stop bit */
+	ret = spi_w8r8(spi, M41T94_REG_SECONDS);
+	if (ret < 0)
+		return ret;
+	if (ret & M41T94_BIT_STOP) {
+		buf[0] = 0x80 | M41T94_REG_SECONDS;
+		buf[1] = ret & ~M41T94_BIT_STOP;
+		spi_write(spi, buf, 2);
+	}
+
+	tm->tm_sec  = bcd2bin(spi_w8r8(spi, M41T94_REG_SECONDS));
+	tm->tm_min  = bcd2bin(spi_w8r8(spi, M41T94_REG_MINUTES));
+	hour = spi_w8r8(spi, M41T94_REG_HOURS);
+	tm->tm_hour = bcd2bin(hour & 0x3f);
+	tm->tm_wday = bcd2bin(spi_w8r8(spi, M41T94_REG_WDAY)) - 1;
+	tm->tm_mday = bcd2bin(spi_w8r8(spi, M41T94_REG_DAY));
+	tm->tm_mon  = bcd2bin(spi_w8r8(spi, M41T94_REG_MONTH)) - 1;
+	tm->tm_year = bcd2bin(spi_w8r8(spi, M41T94_REG_YEAR));
+	if ((hour & M41T94_BIT_CB) || !(hour & M41T94_BIT_CEB))
+		tm->tm_year += 100;
+
+	dev_dbg(dev, "%s secs=%d, mins=%d, "
+		"hours=%d, mday=%d, mon=%d, year=%d, wday=%d\n",
+		"read", tm->tm_sec, tm->tm_min,
+		tm->tm_hour, tm->tm_mday,
+		tm->tm_mon, tm->tm_year, tm->tm_wday);
+
+	return 0;
+}
+
+static const struct rtc_class_ops m41t94_rtc_ops = {
+	.read_time	= m41t94_read_time,
+	.set_time	= m41t94_set_time,
+};
+
+static struct spi_driver m41t94_driver;
+
+static int m41t94_probe(struct spi_device *spi)
+{
+	struct rtc_device *rtc;
+	int res;
+
+	spi->bits_per_word = 8;
+	spi_setup(spi);
+
+	res = spi_w8r8(spi, M41T94_REG_SECONDS);
+	if (res < 0) {
+		dev_err(&spi->dev, "not found.\n");
+		return res;
+	}
+
+	rtc = devm_rtc_device_register(&spi->dev, m41t94_driver.driver.name,
+					&m41t94_rtc_ops, THIS_MODULE);
+	if (IS_ERR(rtc))
+		return PTR_ERR(rtc);
+
+	spi_set_drvdata(spi, rtc);
+
+	return 0;
+}
+
+static struct spi_driver m41t94_driver = {
+	.driver = {
+		.name	= "rtc-m41t94",
+	},
+	.probe	= m41t94_probe,
+};
+
+module_spi_driver(m41t94_driver);
+
+MODULE_AUTHOR("Kim B. Heino <Kim.Heino@bluegiga.com>");
+MODULE_DESCRIPTION("Driver for ST M41T94 SPI RTC");
+MODULE_LICENSE("GPL");
+MODULE_ALIAS("spi:rtc-m41t94");