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, 358 insertions, 0 deletions

diff --git a/drivers/rtc/rtc-ds1286.c b/drivers/rtc/rtc-ds1286.c
new file mode 100644
index 000000000..7acf849d4
--- /dev/null
+++ b/drivers/rtc/rtc-ds1286.c
@@ -0,0 +1,358 @@
+// SPDX-License-Identifier: GPL-2.0-or-later
+/*
+ * DS1286 Real Time Clock interface for Linux
+ *
+ * Copyright (C) 1998, 1999, 2000 Ralf Baechle
+ * Copyright (C) 2008 Thomas Bogendoerfer
+ *
+ * Based on code written by Paul Gortmaker.
+ */
+
+#include <linux/module.h>
+#include <linux/rtc.h>
+#include <linux/platform_device.h>
+#include <linux/bcd.h>
+#include <linux/rtc/ds1286.h>
+#include <linux/io.h>
+#include <linux/slab.h>
+
+struct ds1286_priv {
+	struct rtc_device *rtc;
+	u32 __iomem *rtcregs;
+	spinlock_t lock;
+};
+
+static inline u8 ds1286_rtc_read(struct ds1286_priv *priv, int reg)
+{
+	return __raw_readl(&priv->rtcregs[reg]) & 0xff;
+}
+
+static inline void ds1286_rtc_write(struct ds1286_priv *priv, u8 data, int reg)
+{
+	__raw_writel(data, &priv->rtcregs[reg]);
+}
+
+
+static int ds1286_alarm_irq_enable(struct device *dev, unsigned int enabled)
+{
+	struct ds1286_priv *priv = dev_get_drvdata(dev);
+	unsigned long flags;
+	unsigned char val;
+
+	/* Allow or mask alarm interrupts */
+	spin_lock_irqsave(&priv->lock, flags);
+	val = ds1286_rtc_read(priv, RTC_CMD);
+	if (enabled)
+		val &=  ~RTC_TDM;
+	else
+		val |=  RTC_TDM;
+	ds1286_rtc_write(priv, val, RTC_CMD);
+	spin_unlock_irqrestore(&priv->lock, flags);
+
+	return 0;
+}
+
+#ifdef CONFIG_RTC_INTF_DEV
+
+static int ds1286_ioctl(struct device *dev, unsigned int cmd, unsigned long arg)
+{
+	struct ds1286_priv *priv = dev_get_drvdata(dev);
+	unsigned long flags;
+	unsigned char val;
+
+	switch (cmd) {
+	case RTC_WIE_OFF:
+		/* Mask watchdog int. enab. bit	*/
+		spin_lock_irqsave(&priv->lock, flags);
+		val = ds1286_rtc_read(priv, RTC_CMD);
+		val |= RTC_WAM;
+		ds1286_rtc_write(priv, val, RTC_CMD);
+		spin_unlock_irqrestore(&priv->lock, flags);
+		break;
+	case RTC_WIE_ON:
+		/* Allow watchdog interrupts.	*/
+		spin_lock_irqsave(&priv->lock, flags);
+		val = ds1286_rtc_read(priv, RTC_CMD);
+		val &= ~RTC_WAM;
+		ds1286_rtc_write(priv, val, RTC_CMD);
+		spin_unlock_irqrestore(&priv->lock, flags);
+		break;
+	default:
+		return -ENOIOCTLCMD;
+	}
+	return 0;
+}
+
+#else
+#define ds1286_ioctl    NULL
+#endif
+
+#ifdef CONFIG_PROC_FS
+
+static int ds1286_proc(struct device *dev, struct seq_file *seq)
+{
+	struct ds1286_priv *priv = dev_get_drvdata(dev);
+	unsigned char month, cmd, amode;
+	const char *s;
+
+	month = ds1286_rtc_read(priv, RTC_MONTH);
+	seq_printf(seq,
+		   "oscillator\t: %s\n"
+		   "square_wave\t: %s\n",
+		   (month & RTC_EOSC) ? "disabled" : "enabled",
+		   (month & RTC_ESQW) ? "disabled" : "enabled");
+
+	amode = ((ds1286_rtc_read(priv, RTC_MINUTES_ALARM) & 0x80) >> 5) |
+		((ds1286_rtc_read(priv, RTC_HOURS_ALARM) & 0x80) >> 6) |
+		((ds1286_rtc_read(priv, RTC_DAY_ALARM) & 0x80) >> 7);
+	switch (amode) {
+	case 7:
+		s = "each minute";
+		break;
+	case 3:
+		s = "minutes match";
+		break;
+	case 1:
+		s = "hours and minutes match";
+		break;
+	case 0:
+		s = "days, hours and minutes match";
+		break;
+	default:
+		s = "invalid";
+		break;
+	}
+	seq_printf(seq, "alarm_mode\t: %s\n", s);
+
+	cmd = ds1286_rtc_read(priv, RTC_CMD);
+	seq_printf(seq,
+		   "alarm_enable\t: %s\n"
+		   "wdog_alarm\t: %s\n"
+		   "alarm_mask\t: %s\n"
+		   "wdog_alarm_mask\t: %s\n"
+		   "interrupt_mode\t: %s\n"
+		   "INTB_mode\t: %s_active\n"
+		   "interrupt_pins\t: %s\n",
+		   (cmd & RTC_TDF) ? "yes" : "no",
+		   (cmd & RTC_WAF) ? "yes" : "no",
+		   (cmd & RTC_TDM) ? "disabled" : "enabled",
+		   (cmd & RTC_WAM) ? "disabled" : "enabled",
+		   (cmd & RTC_PU_LVL) ? "pulse" : "level",
+		   (cmd & RTC_IBH_LO) ? "low" : "high",
+		   (cmd & RTC_IPSW) ? "unswapped" : "swapped");
+	return 0;
+}
+
+#else
+#define ds1286_proc     NULL
+#endif
+
+static int ds1286_read_time(struct device *dev, struct rtc_time *tm)
+{
+	struct ds1286_priv *priv = dev_get_drvdata(dev);
+	unsigned char save_control;
+	unsigned long flags;
+	unsigned long uip_watchdog = jiffies;
+
+	/*
+	 * read RTC once any update in progress is done. The update
+	 * can take just over 2ms. We wait 10 to 20ms. There is no need to
+	 * to poll-wait (up to 1s - eeccch) for the falling edge of RTC_UIP.
+	 * If you need to know *exactly* when a second has started, enable
+	 * periodic update complete interrupts, (via ioctl) and then
+	 * immediately read /dev/rtc which will block until you get the IRQ.
+	 * Once the read clears, read the RTC time (again via ioctl). Easy.
+	 */
+
+	if (ds1286_rtc_read(priv, RTC_CMD) & RTC_TE)
+		while (time_before(jiffies, uip_watchdog + 2*HZ/100))
+			barrier();
+
+	/*
+	 * 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_irqsave(&priv->lock, flags);
+	save_control = ds1286_rtc_read(priv, RTC_CMD);
+	ds1286_rtc_write(priv, (save_control|RTC_TE), RTC_CMD);
+
+	tm->tm_sec = ds1286_rtc_read(priv, RTC_SECONDS);
+	tm->tm_min = ds1286_rtc_read(priv, RTC_MINUTES);
+	tm->tm_hour = ds1286_rtc_read(priv, RTC_HOURS) & 0x3f;
+	tm->tm_mday = ds1286_rtc_read(priv, RTC_DATE);
+	tm->tm_mon = ds1286_rtc_read(priv, RTC_MONTH) & 0x1f;
+	tm->tm_year = ds1286_rtc_read(priv, RTC_YEAR);
+
+	ds1286_rtc_write(priv, save_control, RTC_CMD);
+	spin_unlock_irqrestore(&priv->lock, flags);
+
+	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;
+	 */
+	if (tm->tm_year < 45)
+		tm->tm_year += 30;
+	tm->tm_year += 40;
+	if (tm->tm_year < 70)
+		tm->tm_year += 100;
+
+	tm->tm_mon--;
+
+	return 0;
+}
+
+static int ds1286_set_time(struct device *dev, struct rtc_time *tm)
+{
+	struct ds1286_priv *priv = dev_get_drvdata(dev);
+	unsigned char mon, day, hrs, min, sec;
+	unsigned char save_control;
+	unsigned int yrs;
+	unsigned long flags;
+
+	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 -= 1940;
+	if (yrs > 255)    /* They are unsigned */
+		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_irqsave(&priv->lock, flags);
+	save_control = ds1286_rtc_read(priv, RTC_CMD);
+	ds1286_rtc_write(priv, (save_control|RTC_TE), RTC_CMD);
+
+	ds1286_rtc_write(priv, yrs, RTC_YEAR);
+	ds1286_rtc_write(priv, mon, RTC_MONTH);
+	ds1286_rtc_write(priv, day, RTC_DATE);
+	ds1286_rtc_write(priv, hrs, RTC_HOURS);
+	ds1286_rtc_write(priv, min, RTC_MINUTES);
+	ds1286_rtc_write(priv, sec, RTC_SECONDS);
+	ds1286_rtc_write(priv, 0, RTC_HUNDREDTH_SECOND);
+
+	ds1286_rtc_write(priv, save_control, RTC_CMD);
+	spin_unlock_irqrestore(&priv->lock, flags);
+	return 0;
+}
+
+static int ds1286_read_alarm(struct device *dev, struct rtc_wkalrm *alm)
+{
+	struct ds1286_priv *priv = dev_get_drvdata(dev);
+	unsigned long flags;
+
+	/*
+	 * Only the values that we read from the RTC are set. That
+	 * means only tm_wday, tm_hour, tm_min.
+	 */
+	spin_lock_irqsave(&priv->lock, flags);
+	alm->time.tm_min = ds1286_rtc_read(priv, RTC_MINUTES_ALARM) & 0x7f;
+	alm->time.tm_hour = ds1286_rtc_read(priv, RTC_HOURS_ALARM)  & 0x1f;
+	alm->time.tm_wday = ds1286_rtc_read(priv, RTC_DAY_ALARM)    & 0x07;
+	ds1286_rtc_read(priv, RTC_CMD);
+	spin_unlock_irqrestore(&priv->lock, flags);
+
+	alm->time.tm_min = bcd2bin(alm->time.tm_min);
+	alm->time.tm_hour = bcd2bin(alm->time.tm_hour);
+	alm->time.tm_sec = 0;
+	return 0;
+}
+
+static int ds1286_set_alarm(struct device *dev, struct rtc_wkalrm *alm)
+{
+	struct ds1286_priv *priv = dev_get_drvdata(dev);
+	unsigned char hrs, min, sec;
+
+	hrs = alm->time.tm_hour;
+	min = alm->time.tm_min;
+	sec = alm->time.tm_sec;
+
+	if (hrs >= 24)
+		hrs = 0xff;
+
+	if (min >= 60)
+		min = 0xff;
+
+	if (sec != 0)
+		return -EINVAL;
+
+	min = bin2bcd(min);
+	hrs = bin2bcd(hrs);
+
+	spin_lock(&priv->lock);
+	ds1286_rtc_write(priv, hrs, RTC_HOURS_ALARM);
+	ds1286_rtc_write(priv, min, RTC_MINUTES_ALARM);
+	spin_unlock(&priv->lock);
+
+	return 0;
+}
+
+static const struct rtc_class_ops ds1286_ops = {
+	.ioctl		= ds1286_ioctl,
+	.proc		= ds1286_proc,
+	.read_time	= ds1286_read_time,
+	.set_time	= ds1286_set_time,
+	.read_alarm	= ds1286_read_alarm,
+	.set_alarm	= ds1286_set_alarm,
+	.alarm_irq_enable = ds1286_alarm_irq_enable,
+};
+
+static int ds1286_probe(struct platform_device *pdev)
+{
+	struct rtc_device *rtc;
+	struct ds1286_priv *priv;
+
+	priv = devm_kzalloc(&pdev->dev, sizeof(struct ds1286_priv), GFP_KERNEL);
+	if (!priv)
+		return -ENOMEM;
+
+	priv->rtcregs = devm_platform_ioremap_resource(pdev, 0);
+	if (IS_ERR(priv->rtcregs))
+		return PTR_ERR(priv->rtcregs);
+
+	spin_lock_init(&priv->lock);
+	platform_set_drvdata(pdev, priv);
+	rtc = devm_rtc_device_register(&pdev->dev, "ds1286", &ds1286_ops,
+					THIS_MODULE);
+	if (IS_ERR(rtc))
+		return PTR_ERR(rtc);
+	priv->rtc = rtc;
+	return 0;
+}
+
+static struct platform_driver ds1286_platform_driver = {
+	.driver		= {
+		.name	= "rtc-ds1286",
+	},
+	.probe		= ds1286_probe,
+};
+
+module_platform_driver(ds1286_platform_driver);
+
+MODULE_AUTHOR("Thomas Bogendoerfer <tsbogend@alpha.franken.de>");
+MODULE_DESCRIPTION("DS1286 RTC driver");
+MODULE_LICENSE("GPL");
+MODULE_ALIAS("platform:rtc-ds1286");