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, 409 insertions, 0 deletions

diff --git a/drivers/rtc/rtc-cros-ec.c b/drivers/rtc/rtc-cros-ec.c
new file mode 100644
index 000000000..f56650899
--- /dev/null
+++ b/drivers/rtc/rtc-cros-ec.c
@@ -0,0 +1,409 @@
+// SPDX-License-Identifier: GPL-2.0
+// RTC driver for ChromeOS Embedded Controller.
+//
+// Copyright (C) 2017 Google, Inc.
+// Author: Stephen Barber <smbarber@chromium.org>
+
+#include <linux/kernel.h>
+#include <linux/module.h>
+#include <linux/platform_data/cros_ec_commands.h>
+#include <linux/platform_data/cros_ec_proto.h>
+#include <linux/platform_device.h>
+#include <linux/rtc.h>
+#include <linux/slab.h>
+
+#define DRV_NAME	"cros-ec-rtc"
+
+#define SECS_PER_DAY	(24 * 60 * 60)
+
+/**
+ * struct cros_ec_rtc - Driver data for EC RTC
+ *
+ * @cros_ec: Pointer to EC device
+ * @rtc: Pointer to RTC device
+ * @notifier: Notifier info for responding to EC events
+ * @saved_alarm: Alarm to restore when interrupts are reenabled
+ */
+struct cros_ec_rtc {
+	struct cros_ec_device *cros_ec;
+	struct rtc_device *rtc;
+	struct notifier_block notifier;
+	u32 saved_alarm;
+};
+
+static int cros_ec_rtc_get(struct cros_ec_device *cros_ec, u32 command,
+			   u32 *response)
+{
+	DEFINE_RAW_FLEX(struct cros_ec_command, msg, data,
+			sizeof(struct ec_response_rtc));
+	int ret;
+
+	msg->command = command;
+	msg->insize = sizeof(struct ec_response_rtc);
+
+	ret = cros_ec_cmd_xfer_status(cros_ec, msg);
+	if (ret < 0)
+		return ret;
+
+	*response = ((struct ec_response_rtc *)msg->data)->time;
+
+	return 0;
+}
+
+static int cros_ec_rtc_set(struct cros_ec_device *cros_ec, u32 command,
+			   u32 param)
+{
+	DEFINE_RAW_FLEX(struct cros_ec_command, msg, data,
+			sizeof(struct ec_response_rtc));
+	int ret;
+
+	msg->command = command;
+	msg->outsize = sizeof(struct ec_response_rtc);
+	((struct ec_response_rtc *)msg->data)->time = param;
+
+	ret = cros_ec_cmd_xfer_status(cros_ec, msg);
+	if (ret < 0)
+		return ret;
+	return 0;
+}
+
+/* Read the current time from the EC. */
+static int cros_ec_rtc_read_time(struct device *dev, struct rtc_time *tm)
+{
+	struct cros_ec_rtc *cros_ec_rtc = dev_get_drvdata(dev);
+	struct cros_ec_device *cros_ec = cros_ec_rtc->cros_ec;
+	int ret;
+	u32 time;
+
+	ret = cros_ec_rtc_get(cros_ec, EC_CMD_RTC_GET_VALUE, &time);
+	if (ret) {
+		dev_err(dev, "error getting time: %d\n", ret);
+		return ret;
+	}
+
+	rtc_time64_to_tm(time, tm);
+
+	return 0;
+}
+
+/* Set the current EC time. */
+static int cros_ec_rtc_set_time(struct device *dev, struct rtc_time *tm)
+{
+	struct cros_ec_rtc *cros_ec_rtc = dev_get_drvdata(dev);
+	struct cros_ec_device *cros_ec = cros_ec_rtc->cros_ec;
+	int ret;
+	time64_t time = rtc_tm_to_time64(tm);
+
+	ret = cros_ec_rtc_set(cros_ec, EC_CMD_RTC_SET_VALUE, (u32)time);
+	if (ret < 0) {
+		dev_err(dev, "error setting time: %d\n", ret);
+		return ret;
+	}
+
+	return 0;
+}
+
+/* Read alarm time from RTC. */
+static int cros_ec_rtc_read_alarm(struct device *dev, struct rtc_wkalrm *alrm)
+{
+	struct cros_ec_rtc *cros_ec_rtc = dev_get_drvdata(dev);
+	struct cros_ec_device *cros_ec = cros_ec_rtc->cros_ec;
+	int ret;
+	u32 current_time, alarm_offset;
+
+	/*
+	 * The EC host command for getting the alarm is relative (i.e. 5
+	 * seconds from now) whereas rtc_wkalrm is absolute. Get the current
+	 * RTC time first so we can calculate the relative time.
+	 */
+	ret = cros_ec_rtc_get(cros_ec, EC_CMD_RTC_GET_VALUE, &current_time);
+	if (ret < 0) {
+		dev_err(dev, "error getting time: %d\n", ret);
+		return ret;
+	}
+
+	ret = cros_ec_rtc_get(cros_ec, EC_CMD_RTC_GET_ALARM, &alarm_offset);
+	if (ret < 0) {
+		dev_err(dev, "error getting alarm: %d\n", ret);
+		return ret;
+	}
+
+	rtc_time64_to_tm(current_time + alarm_offset, &alrm->time);
+
+	return 0;
+}
+
+/* Set the EC's RTC alarm. */
+static int cros_ec_rtc_set_alarm(struct device *dev, struct rtc_wkalrm *alrm)
+{
+	struct cros_ec_rtc *cros_ec_rtc = dev_get_drvdata(dev);
+	struct cros_ec_device *cros_ec = cros_ec_rtc->cros_ec;
+	int ret;
+	time64_t alarm_time;
+	u32 current_time, alarm_offset;
+
+	/*
+	 * The EC host command for setting the alarm is relative
+	 * (i.e. 5 seconds from now) whereas rtc_wkalrm is absolute.
+	 * Get the current RTC time first so we can calculate the
+	 * relative time.
+	 */
+	ret = cros_ec_rtc_get(cros_ec, EC_CMD_RTC_GET_VALUE, &current_time);
+	if (ret < 0) {
+		dev_err(dev, "error getting time: %d\n", ret);
+		return ret;
+	}
+
+	alarm_time = rtc_tm_to_time64(&alrm->time);
+
+	if (alarm_time < 0 || alarm_time > U32_MAX)
+		return -EINVAL;
+
+	if (!alrm->enabled) {
+		/*
+		 * If the alarm is being disabled, send an alarm
+		 * clear command.
+		 */
+		alarm_offset = EC_RTC_ALARM_CLEAR;
+		cros_ec_rtc->saved_alarm = (u32)alarm_time;
+	} else {
+		/* Don't set an alarm in the past. */
+		if ((u32)alarm_time <= current_time)
+			return -ETIME;
+
+		alarm_offset = (u32)alarm_time - current_time;
+	}
+
+	ret = cros_ec_rtc_set(cros_ec, EC_CMD_RTC_SET_ALARM, alarm_offset);
+	if (ret < 0) {
+		dev_err(dev, "error setting alarm in %u seconds: %d\n",
+			alarm_offset, ret);
+		/*
+		 * The EC code returns -EINVAL if the alarm time is too
+		 * far in the future. Convert it to the expected error code.
+		 */
+		if (ret == -EINVAL)
+			ret = -ERANGE;
+		return ret;
+	}
+
+	return 0;
+}
+
+static int cros_ec_rtc_alarm_irq_enable(struct device *dev,
+					unsigned int enabled)
+{
+	struct cros_ec_rtc *cros_ec_rtc = dev_get_drvdata(dev);
+	struct cros_ec_device *cros_ec = cros_ec_rtc->cros_ec;
+	int ret;
+	u32 current_time, alarm_offset, alarm_value;
+
+	ret = cros_ec_rtc_get(cros_ec, EC_CMD_RTC_GET_VALUE, &current_time);
+	if (ret < 0) {
+		dev_err(dev, "error getting time: %d\n", ret);
+		return ret;
+	}
+
+	if (enabled) {
+		/* Restore saved alarm if it's still in the future. */
+		if (cros_ec_rtc->saved_alarm < current_time)
+			alarm_offset = EC_RTC_ALARM_CLEAR;
+		else
+			alarm_offset = cros_ec_rtc->saved_alarm - current_time;
+
+		ret = cros_ec_rtc_set(cros_ec, EC_CMD_RTC_SET_ALARM,
+				      alarm_offset);
+		if (ret < 0) {
+			dev_err(dev, "error restoring alarm: %d\n", ret);
+			return ret;
+		}
+	} else {
+		/* Disable alarm, saving the old alarm value. */
+		ret = cros_ec_rtc_get(cros_ec, EC_CMD_RTC_GET_ALARM,
+				      &alarm_offset);
+		if (ret < 0) {
+			dev_err(dev, "error saving alarm: %d\n", ret);
+			return ret;
+		}
+
+		alarm_value = current_time + alarm_offset;
+
+		/*
+		 * If the current EC alarm is already past, we don't want
+		 * to set an alarm when we go through the alarm irq enable
+		 * path.
+		 */
+		if (alarm_value < current_time)
+			cros_ec_rtc->saved_alarm = EC_RTC_ALARM_CLEAR;
+		else
+			cros_ec_rtc->saved_alarm = alarm_value;
+
+		alarm_offset = EC_RTC_ALARM_CLEAR;
+		ret = cros_ec_rtc_set(cros_ec, EC_CMD_RTC_SET_ALARM,
+				      alarm_offset);
+		if (ret < 0) {
+			dev_err(dev, "error disabling alarm: %d\n", ret);
+			return ret;
+		}
+	}
+
+	return 0;
+}
+
+static int cros_ec_rtc_event(struct notifier_block *nb,
+			     unsigned long queued_during_suspend,
+			     void *_notify)
+{
+	struct cros_ec_rtc *cros_ec_rtc;
+	struct rtc_device *rtc;
+	struct cros_ec_device *cros_ec;
+	u32 host_event;
+
+	cros_ec_rtc = container_of(nb, struct cros_ec_rtc, notifier);
+	rtc = cros_ec_rtc->rtc;
+	cros_ec = cros_ec_rtc->cros_ec;
+
+	host_event = cros_ec_get_host_event(cros_ec);
+	if (host_event & EC_HOST_EVENT_MASK(EC_HOST_EVENT_RTC)) {
+		rtc_update_irq(rtc, 1, RTC_IRQF | RTC_AF);
+		return NOTIFY_OK;
+	} else {
+		return NOTIFY_DONE;
+	}
+}
+
+static const struct rtc_class_ops cros_ec_rtc_ops = {
+	.read_time = cros_ec_rtc_read_time,
+	.set_time = cros_ec_rtc_set_time,
+	.read_alarm = cros_ec_rtc_read_alarm,
+	.set_alarm = cros_ec_rtc_set_alarm,
+	.alarm_irq_enable = cros_ec_rtc_alarm_irq_enable,
+};
+
+#ifdef CONFIG_PM_SLEEP
+static int cros_ec_rtc_suspend(struct device *dev)
+{
+	struct platform_device *pdev = to_platform_device(dev);
+	struct cros_ec_rtc *cros_ec_rtc = dev_get_drvdata(&pdev->dev);
+
+	if (device_may_wakeup(dev))
+		return enable_irq_wake(cros_ec_rtc->cros_ec->irq);
+
+	return 0;
+}
+
+static int cros_ec_rtc_resume(struct device *dev)
+{
+	struct platform_device *pdev = to_platform_device(dev);
+	struct cros_ec_rtc *cros_ec_rtc = dev_get_drvdata(&pdev->dev);
+
+	if (device_may_wakeup(dev))
+		return disable_irq_wake(cros_ec_rtc->cros_ec->irq);
+
+	return 0;
+}
+#endif
+
+static SIMPLE_DEV_PM_OPS(cros_ec_rtc_pm_ops, cros_ec_rtc_suspend,
+			 cros_ec_rtc_resume);
+
+static int cros_ec_rtc_probe(struct platform_device *pdev)
+{
+	struct cros_ec_dev *ec_dev = dev_get_drvdata(pdev->dev.parent);
+	struct cros_ec_device *cros_ec = ec_dev->ec_dev;
+	struct cros_ec_rtc *cros_ec_rtc;
+	struct rtc_time tm;
+	int ret;
+
+	cros_ec_rtc = devm_kzalloc(&pdev->dev, sizeof(*cros_ec_rtc),
+				   GFP_KERNEL);
+	if (!cros_ec_rtc)
+		return -ENOMEM;
+
+	platform_set_drvdata(pdev, cros_ec_rtc);
+	cros_ec_rtc->cros_ec = cros_ec;
+
+	/* Get initial time */
+	ret = cros_ec_rtc_read_time(&pdev->dev, &tm);
+	if (ret) {
+		dev_err(&pdev->dev, "failed to read RTC time\n");
+		return ret;
+	}
+
+	ret = device_init_wakeup(&pdev->dev, true);
+	if (ret) {
+		dev_err(&pdev->dev, "failed to initialize wakeup\n");
+		return ret;
+	}
+
+	cros_ec_rtc->rtc = devm_rtc_allocate_device(&pdev->dev);
+	if (IS_ERR(cros_ec_rtc->rtc))
+		return PTR_ERR(cros_ec_rtc->rtc);
+
+	cros_ec_rtc->rtc->ops = &cros_ec_rtc_ops;
+	cros_ec_rtc->rtc->range_max = U32_MAX;
+
+	/*
+	 * The RTC on some older Chromebooks can only handle alarms less than
+	 * 24 hours in the future. The only way to find out is to try to set an
+	 * alarm further in the future. If that fails, assume that the RTC
+	 * connected to the EC can only handle less than 24 hours of alarm
+	 * window.
+	 */
+	ret = cros_ec_rtc_set(cros_ec, EC_CMD_RTC_SET_ALARM, SECS_PER_DAY * 2);
+	if (ret == -EINVAL)
+		cros_ec_rtc->rtc->alarm_offset_max = SECS_PER_DAY - 1;
+
+	(void)cros_ec_rtc_set(cros_ec, EC_CMD_RTC_SET_ALARM,
+			      EC_RTC_ALARM_CLEAR);
+
+	ret = devm_rtc_register_device(cros_ec_rtc->rtc);
+	if (ret)
+		return ret;
+
+	/* Get RTC events from the EC. */
+	cros_ec_rtc->notifier.notifier_call = cros_ec_rtc_event;
+	ret = blocking_notifier_chain_register(&cros_ec->event_notifier,
+					       &cros_ec_rtc->notifier);
+	if (ret) {
+		dev_err(&pdev->dev, "failed to register notifier\n");
+		return ret;
+	}
+
+	return 0;
+}
+
+static void cros_ec_rtc_remove(struct platform_device *pdev)
+{
+	struct cros_ec_rtc *cros_ec_rtc = platform_get_drvdata(pdev);
+	struct device *dev = &pdev->dev;
+	int ret;
+
+	ret = blocking_notifier_chain_unregister(
+				&cros_ec_rtc->cros_ec->event_notifier,
+				&cros_ec_rtc->notifier);
+	if (ret)
+		dev_err(dev, "failed to unregister notifier\n");
+}
+
+static const struct platform_device_id cros_ec_rtc_id[] = {
+	{ .name = DRV_NAME },
+	{ }
+};
+MODULE_DEVICE_TABLE(platform, cros_ec_rtc_id);
+
+static struct platform_driver cros_ec_rtc_driver = {
+	.probe = cros_ec_rtc_probe,
+	.remove = cros_ec_rtc_remove,
+	.driver = {
+		.name = DRV_NAME,
+		.pm = &cros_ec_rtc_pm_ops,
+	},
+	.id_table = cros_ec_rtc_id,
+};
+
+module_platform_driver(cros_ec_rtc_driver);
+
+MODULE_DESCRIPTION("RTC driver for Chrome OS ECs");
+MODULE_AUTHOR("Stephen Barber <smbarber@chromium.org>");
+MODULE_LICENSE("GPL v2");