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, 193 insertions, 0 deletions

diff --git a/drivers/rtc/rtc-m48t35.c b/drivers/rtc/rtc-m48t35.c
new file mode 100644
index 000000000..92f19bf99
--- /dev/null
+++ b/drivers/rtc/rtc-m48t35.c
@@ -0,0 +1,193 @@
+// SPDX-License-Identifier: GPL-2.0-or-later
+/*
+ * Driver for the SGS-Thomson M48T35 Timekeeper RAM chip
+ *
+ * Copyright (C) 2000 Silicon Graphics, Inc.
+ * Written by Ulf Carlsson (ulfc@engr.sgi.com)
+ *
+ * Copyright (C) 2008 Thomas Bogendoerfer
+ *
+ * Based on code written by Paul Gortmaker.
+ */
+
+#include <linux/module.h>
+#include <linux/rtc.h>
+#include <linux/slab.h>
+#include <linux/platform_device.h>
+#include <linux/bcd.h>
+#include <linux/io.h>
+#include <linux/err.h>
+
+struct m48t35_rtc {
+	u8	pad[0x7ff8];    /* starts at 0x7ff8 */
+#ifdef CONFIG_SGI_IP27
+	u8	hour;
+	u8	min;
+	u8	sec;
+	u8	control;
+	u8	year;
+	u8	month;
+	u8	date;
+	u8	day;
+#else
+	u8	control;
+	u8	sec;
+	u8	min;
+	u8	hour;
+	u8	day;
+	u8	date;
+	u8	month;
+	u8	year;
+#endif
+};
+
+#define M48T35_RTC_SET		0x80
+#define M48T35_RTC_READ		0x40
+
+struct m48t35_priv {
+	struct rtc_device *rtc;
+	struct m48t35_rtc __iomem *reg;
+	size_t size;
+	unsigned long baseaddr;
+	spinlock_t lock;
+};
+
+static int m48t35_read_time(struct device *dev, struct rtc_time *tm)
+{
+	struct m48t35_priv *priv = dev_get_drvdata(dev);
+	u8 control;
+
+	/*
+	 * Only the values that we read from the RTC are set. We leave
+	 * tm_wday, tm_yday and tm_isdst untouched. Even though the
+	 * RTC has RTC_DAY_OF_WEEK, we ignore it, as it is only updated
+	 * by the RTC when initially set to a non-zero value.
+	 */
+	spin_lock_irq(&priv->lock);
+	control = readb(&priv->reg->control);
+	writeb(control | M48T35_RTC_READ, &priv->reg->control);
+	tm->tm_sec = readb(&priv->reg->sec);
+	tm->tm_min = readb(&priv->reg->min);
+	tm->tm_hour = readb(&priv->reg->hour);
+	tm->tm_mday = readb(&priv->reg->date);
+	tm->tm_mon = readb(&priv->reg->month);
+	tm->tm_year = readb(&priv->reg->year);
+	writeb(control, &priv->reg->control);
+	spin_unlock_irq(&priv->lock);
+
+	tm->tm_sec = bcd2bin(tm->tm_sec);
+	tm->tm_min = bcd2bin(tm->tm_min);
+	tm->tm_hour = bcd2bin(tm->tm_hour);
+	tm->tm_mday = bcd2bin(tm->tm_mday);
+	tm->tm_mon = bcd2bin(tm->tm_mon);
+	tm->tm_year = bcd2bin(tm->tm_year);
+
+	/*
+	 * Account for differences between how the RTC uses the values
+	 * and how they are defined in a struct rtc_time;
+	 */
+	tm->tm_year += 70;
+	if (tm->tm_year <= 69)
+		tm->tm_year += 100;
+
+	tm->tm_mon--;
+	return 0;
+}
+
+static int m48t35_set_time(struct device *dev, struct rtc_time *tm)
+{
+	struct m48t35_priv *priv = dev_get_drvdata(dev);
+	unsigned char mon, day, hrs, min, sec;
+	unsigned int yrs;
+	u8 control;
+
+	yrs = tm->tm_year + 1900;
+	mon = tm->tm_mon + 1;   /* tm_mon starts at zero */
+	day = tm->tm_mday;
+	hrs = tm->tm_hour;
+	min = tm->tm_min;
+	sec = tm->tm_sec;
+
+	if (yrs < 1970)
+		return -EINVAL;
+
+	yrs -= 1970;
+	if (yrs > 255)    /* They are unsigned */
+		return -EINVAL;
+
+	if (yrs > 169)
+		return -EINVAL;
+
+	if (yrs >= 100)
+		yrs -= 100;
+
+	sec = bin2bcd(sec);
+	min = bin2bcd(min);
+	hrs = bin2bcd(hrs);
+	day = bin2bcd(day);
+	mon = bin2bcd(mon);
+	yrs = bin2bcd(yrs);
+
+	spin_lock_irq(&priv->lock);
+	control = readb(&priv->reg->control);
+	writeb(control | M48T35_RTC_SET, &priv->reg->control);
+	writeb(yrs, &priv->reg->year);
+	writeb(mon, &priv->reg->month);
+	writeb(day, &priv->reg->date);
+	writeb(hrs, &priv->reg->hour);
+	writeb(min, &priv->reg->min);
+	writeb(sec, &priv->reg->sec);
+	writeb(control, &priv->reg->control);
+	spin_unlock_irq(&priv->lock);
+	return 0;
+}
+
+static const struct rtc_class_ops m48t35_ops = {
+	.read_time	= m48t35_read_time,
+	.set_time	= m48t35_set_time,
+};
+
+static int m48t35_probe(struct platform_device *pdev)
+{
+	struct resource *res;
+	struct m48t35_priv *priv;
+
+	res = platform_get_resource(pdev, IORESOURCE_MEM, 0);
+	if (!res)
+		return -ENODEV;
+	priv = devm_kzalloc(&pdev->dev, sizeof(struct m48t35_priv), GFP_KERNEL);
+	if (!priv)
+		return -ENOMEM;
+
+	priv->size = resource_size(res);
+	if (!devm_request_mem_region(&pdev->dev, res->start, priv->size,
+				     pdev->name))
+		return -EBUSY;
+
+	priv->baseaddr = res->start;
+	priv->reg = devm_ioremap(&pdev->dev, priv->baseaddr, priv->size);
+	if (!priv->reg)
+		return -ENOMEM;
+
+	spin_lock_init(&priv->lock);
+
+	platform_set_drvdata(pdev, priv);
+
+	priv->rtc = devm_rtc_device_register(&pdev->dev, "m48t35",
+				  &m48t35_ops, THIS_MODULE);
+	return PTR_ERR_OR_ZERO(priv->rtc);
+}
+
+static struct platform_driver m48t35_platform_driver = {
+	.driver		= {
+		.name	= "rtc-m48t35",
+	},
+	.probe		= m48t35_probe,
+};
+
+module_platform_driver(m48t35_platform_driver);
+
+MODULE_AUTHOR("Thomas Bogendoerfer <tsbogend@alpha.franken.de>");
+MODULE_DESCRIPTION("M48T35 RTC driver");
+MODULE_LICENSE("GPL");
+MODULE_ALIAS("platform:rtc-m48t35");