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, 311 insertions, 0 deletions

diff --git a/drivers/rtc/rtc-st-lpc.c b/drivers/rtc/rtc-st-lpc.c
new file mode 100644
index 000000000..ae79ddf24
--- /dev/null
+++ b/drivers/rtc/rtc-st-lpc.c
@@ -0,0 +1,311 @@
+// SPDX-License-Identifier: GPL-2.0-or-later
+/*
+ * rtc-st-lpc.c - ST's LPC RTC, powered by the Low Power Timer
+ *
+ * Copyright (C) 2014 STMicroelectronics Limited
+ *
+ * Author: David Paris <david.paris@st.com> for STMicroelectronics
+ *         Lee Jones <lee.jones@linaro.org> for STMicroelectronics
+ *
+ * Based on the original driver written by Stuart Menefy.
+ */
+
+#include <linux/clk.h>
+#include <linux/delay.h>
+#include <linux/init.h>
+#include <linux/io.h>
+#include <linux/irq.h>
+#include <linux/kernel.h>
+#include <linux/module.h>
+#include <linux/of.h>
+#include <linux/platform_device.h>
+#include <linux/rtc.h>
+
+#include <dt-bindings/mfd/st-lpc.h>
+
+/* Low Power Timer */
+#define LPC_LPT_LSB_OFF		0x400
+#define LPC_LPT_MSB_OFF		0x404
+#define LPC_LPT_START_OFF	0x408
+
+/* Low Power Alarm */
+#define LPC_LPA_LSB_OFF		0x410
+#define LPC_LPA_MSB_OFF		0x414
+#define LPC_LPA_START_OFF	0x418
+
+/* LPC as WDT */
+#define LPC_WDT_OFF		0x510
+#define LPC_WDT_FLAG_OFF	0x514
+
+struct st_rtc {
+	struct rtc_device *rtc_dev;
+	struct rtc_wkalrm alarm;
+	struct clk *clk;
+	unsigned long clkrate;
+	void __iomem *ioaddr;
+	bool irq_enabled:1;
+	spinlock_t lock;
+	short irq;
+};
+
+static void st_rtc_set_hw_alarm(struct st_rtc *rtc,
+				unsigned long msb, unsigned long  lsb)
+{
+	unsigned long flags;
+
+	spin_lock_irqsave(&rtc->lock, flags);
+
+	writel_relaxed(1, rtc->ioaddr + LPC_WDT_OFF);
+
+	writel_relaxed(msb, rtc->ioaddr + LPC_LPA_MSB_OFF);
+	writel_relaxed(lsb, rtc->ioaddr + LPC_LPA_LSB_OFF);
+	writel_relaxed(1, rtc->ioaddr + LPC_LPA_START_OFF);
+
+	writel_relaxed(0, rtc->ioaddr + LPC_WDT_OFF);
+
+	spin_unlock_irqrestore(&rtc->lock, flags);
+}
+
+static irqreturn_t st_rtc_handler(int this_irq, void *data)
+{
+	struct st_rtc *rtc = (struct st_rtc *)data;
+
+	rtc_update_irq(rtc->rtc_dev, 1, RTC_AF);
+
+	return IRQ_HANDLED;
+}
+
+static int st_rtc_read_time(struct device *dev, struct rtc_time *tm)
+{
+	struct st_rtc *rtc = dev_get_drvdata(dev);
+	unsigned long lpt_lsb, lpt_msb;
+	unsigned long long lpt;
+	unsigned long flags;
+
+	spin_lock_irqsave(&rtc->lock, flags);
+
+	do {
+		lpt_msb = readl_relaxed(rtc->ioaddr + LPC_LPT_MSB_OFF);
+		lpt_lsb = readl_relaxed(rtc->ioaddr + LPC_LPT_LSB_OFF);
+	} while (readl_relaxed(rtc->ioaddr + LPC_LPT_MSB_OFF) != lpt_msb);
+
+	spin_unlock_irqrestore(&rtc->lock, flags);
+
+	lpt = ((unsigned long long)lpt_msb << 32) | lpt_lsb;
+	do_div(lpt, rtc->clkrate);
+	rtc_time64_to_tm(lpt, tm);
+
+	return 0;
+}
+
+static int st_rtc_set_time(struct device *dev, struct rtc_time *tm)
+{
+	struct st_rtc *rtc = dev_get_drvdata(dev);
+	unsigned long long lpt, secs;
+	unsigned long flags;
+
+	secs = rtc_tm_to_time64(tm);
+
+	lpt = (unsigned long long)secs * rtc->clkrate;
+
+	spin_lock_irqsave(&rtc->lock, flags);
+
+	writel_relaxed(lpt >> 32, rtc->ioaddr + LPC_LPT_MSB_OFF);
+	writel_relaxed(lpt, rtc->ioaddr + LPC_LPT_LSB_OFF);
+	writel_relaxed(1, rtc->ioaddr + LPC_LPT_START_OFF);
+
+	spin_unlock_irqrestore(&rtc->lock, flags);
+
+	return 0;
+}
+
+static int st_rtc_read_alarm(struct device *dev, struct rtc_wkalrm *wkalrm)
+{
+	struct st_rtc *rtc = dev_get_drvdata(dev);
+	unsigned long flags;
+
+	spin_lock_irqsave(&rtc->lock, flags);
+
+	memcpy(wkalrm, &rtc->alarm, sizeof(struct rtc_wkalrm));
+
+	spin_unlock_irqrestore(&rtc->lock, flags);
+
+	return 0;
+}
+
+static int st_rtc_alarm_irq_enable(struct device *dev, unsigned int enabled)
+{
+	struct st_rtc *rtc = dev_get_drvdata(dev);
+
+	if (enabled && !rtc->irq_enabled) {
+		enable_irq(rtc->irq);
+		rtc->irq_enabled = true;
+	} else if (!enabled && rtc->irq_enabled) {
+		disable_irq(rtc->irq);
+		rtc->irq_enabled = false;
+	}
+
+	return 0;
+}
+
+static int st_rtc_set_alarm(struct device *dev, struct rtc_wkalrm *t)
+{
+	struct st_rtc *rtc = dev_get_drvdata(dev);
+	struct rtc_time now;
+	unsigned long long now_secs;
+	unsigned long long alarm_secs;
+	unsigned long long lpa;
+
+	st_rtc_read_time(dev, &now);
+	now_secs = rtc_tm_to_time64(&now);
+	alarm_secs = rtc_tm_to_time64(&t->time);
+
+	memcpy(&rtc->alarm, t, sizeof(struct rtc_wkalrm));
+
+	/* Now many secs to fire */
+	alarm_secs -= now_secs;
+	lpa = (unsigned long long)alarm_secs * rtc->clkrate;
+
+	st_rtc_set_hw_alarm(rtc, lpa >> 32, lpa);
+	st_rtc_alarm_irq_enable(dev, t->enabled);
+
+	return 0;
+}
+
+static const struct rtc_class_ops st_rtc_ops = {
+	.read_time		= st_rtc_read_time,
+	.set_time		= st_rtc_set_time,
+	.read_alarm		= st_rtc_read_alarm,
+	.set_alarm		= st_rtc_set_alarm,
+	.alarm_irq_enable	= st_rtc_alarm_irq_enable,
+};
+
+static int st_rtc_probe(struct platform_device *pdev)
+{
+	struct device_node *np = pdev->dev.of_node;
+	struct st_rtc *rtc;
+	uint32_t mode;
+	int ret = 0;
+
+	ret = of_property_read_u32(np, "st,lpc-mode", &mode);
+	if (ret) {
+		dev_err(&pdev->dev, "An LPC mode must be provided\n");
+		return -EINVAL;
+	}
+
+	/* LPC can either run as a Clocksource or in RTC or WDT mode */
+	if (mode != ST_LPC_MODE_RTC)
+		return -ENODEV;
+
+	rtc = devm_kzalloc(&pdev->dev, sizeof(struct st_rtc), GFP_KERNEL);
+	if (!rtc)
+		return -ENOMEM;
+
+	rtc->rtc_dev = devm_rtc_allocate_device(&pdev->dev);
+	if (IS_ERR(rtc->rtc_dev))
+		return PTR_ERR(rtc->rtc_dev);
+
+	spin_lock_init(&rtc->lock);
+
+	rtc->ioaddr = devm_platform_ioremap_resource(pdev, 0);
+	if (IS_ERR(rtc->ioaddr))
+		return PTR_ERR(rtc->ioaddr);
+
+	rtc->irq = platform_get_irq(pdev, 0);
+	if (rtc->irq < 0)
+		return rtc->irq;
+
+	ret = devm_request_irq(&pdev->dev, rtc->irq, st_rtc_handler,
+			       IRQF_NO_AUTOEN, pdev->name, rtc);
+	if (ret) {
+		dev_err(&pdev->dev, "Failed to request irq %i\n", rtc->irq);
+		return ret;
+	}
+
+	enable_irq_wake(rtc->irq);
+
+	rtc->clk = devm_clk_get_enabled(&pdev->dev, NULL);
+	if (IS_ERR(rtc->clk))
+		return dev_err_probe(&pdev->dev, PTR_ERR(rtc->clk),
+				     "Unable to request clock\n");
+
+	rtc->clkrate = clk_get_rate(rtc->clk);
+	if (!rtc->clkrate) {
+		dev_err(&pdev->dev, "Unable to fetch clock rate\n");
+		return -EINVAL;
+	}
+
+	device_set_wakeup_capable(&pdev->dev, 1);
+
+	platform_set_drvdata(pdev, rtc);
+
+	rtc->rtc_dev->ops = &st_rtc_ops;
+	rtc->rtc_dev->range_max = U64_MAX;
+	do_div(rtc->rtc_dev->range_max, rtc->clkrate);
+
+	ret = devm_rtc_register_device(rtc->rtc_dev);
+	if (ret)
+		return ret;
+
+	return 0;
+}
+
+#ifdef CONFIG_PM_SLEEP
+static int st_rtc_suspend(struct device *dev)
+{
+	struct st_rtc *rtc = dev_get_drvdata(dev);
+
+	if (device_may_wakeup(dev))
+		return 0;
+
+	writel_relaxed(1, rtc->ioaddr + LPC_WDT_OFF);
+	writel_relaxed(0, rtc->ioaddr + LPC_LPA_START_OFF);
+	writel_relaxed(0, rtc->ioaddr + LPC_WDT_OFF);
+
+	return 0;
+}
+
+static int st_rtc_resume(struct device *dev)
+{
+	struct st_rtc *rtc = dev_get_drvdata(dev);
+
+	rtc_alarm_irq_enable(rtc->rtc_dev, 0);
+
+	/*
+	 * clean 'rtc->alarm' to allow a new
+	 * .set_alarm to the upper RTC layer
+	 */
+	memset(&rtc->alarm, 0, sizeof(struct rtc_wkalrm));
+
+	writel_relaxed(0, rtc->ioaddr + LPC_LPA_MSB_OFF);
+	writel_relaxed(0, rtc->ioaddr + LPC_LPA_LSB_OFF);
+	writel_relaxed(1, rtc->ioaddr + LPC_WDT_OFF);
+	writel_relaxed(1, rtc->ioaddr + LPC_LPA_START_OFF);
+	writel_relaxed(0, rtc->ioaddr + LPC_WDT_OFF);
+
+	return 0;
+}
+#endif
+
+static SIMPLE_DEV_PM_OPS(st_rtc_pm_ops, st_rtc_suspend, st_rtc_resume);
+
+static const struct of_device_id st_rtc_match[] = {
+	{ .compatible = "st,stih407-lpc" },
+	{}
+};
+MODULE_DEVICE_TABLE(of, st_rtc_match);
+
+static struct platform_driver st_rtc_platform_driver = {
+	.driver = {
+		.name = "st-lpc-rtc",
+		.pm = &st_rtc_pm_ops,
+		.of_match_table = st_rtc_match,
+	},
+	.probe = st_rtc_probe,
+};
+
+module_platform_driver(st_rtc_platform_driver);
+
+MODULE_DESCRIPTION("STMicroelectronics LPC RTC driver");
+MODULE_AUTHOR("David Paris <david.paris@st.com>");
+MODULE_LICENSE("GPL");