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, 797 insertions, 0 deletions

diff --git a/drivers/ptp/ptp_vmclock.c b/drivers/ptp/ptp_vmclock.c
new file mode 100644
index 000000000..bb0e14bac
--- /dev/null
+++ b/drivers/ptp/ptp_vmclock.c
@@ -0,0 +1,797 @@
+// SPDX-License-Identifier: GPL-2.0-or-later
+/*
+ * Virtual PTP 1588 clock for use with LM-safe VMclock device.
+ *
+ * Copyright © 2024 Amazon.com, Inc. or its affiliates.
+ */
+
+#include "linux/poll.h"
+#include "linux/types.h"
+#include "linux/wait.h"
+#include <linux/acpi.h>
+#include <linux/device.h>
+#include <linux/err.h>
+#include <linux/file.h>
+#include <linux/fs.h>
+#include <linux/init.h>
+#include <linux/io.h>
+#include <linux/interrupt.h>
+#include <linux/kernel.h>
+#include <linux/miscdevice.h>
+#include <linux/mm.h>
+#include <linux/module.h>
+#include <linux/of.h>
+#include <linux/platform_device.h>
+#include <linux/slab.h>
+
+#include <uapi/linux/vmclock-abi.h>
+
+#include <linux/ptp_clock_kernel.h>
+
+#ifdef CONFIG_X86
+#include <asm/pvclock.h>
+#include <asm/kvmclock.h>
+#endif
+
+#ifdef CONFIG_KVM_GUEST
+#define SUPPORT_KVMCLOCK
+#endif
+
+static DEFINE_IDA(vmclock_ida);
+
+ACPI_MODULE_NAME("vmclock");
+
+struct vmclock_state {
+	struct resource res;
+	struct vmclock_abi *clk;
+	struct miscdevice miscdev;
+	wait_queue_head_t disrupt_wait;
+	struct ptp_clock_info ptp_clock_info;
+	struct ptp_clock *ptp_clock;
+	enum clocksource_ids cs_id, sys_cs_id;
+	int index;
+	char *name;
+};
+
+#define VMCLOCK_MAX_WAIT ms_to_ktime(100)
+
+/* Require at least the flags field to be present. All else can be optional. */
+#define VMCLOCK_MIN_SIZE offsetof(struct vmclock_abi, pad)
+
+#define VMCLOCK_FIELD_PRESENT(_c, _f)			  \
+	(le32_to_cpu((_c)->size) >= (offsetof(struct vmclock_abi, _f) +	\
+				     sizeof((_c)->_f)))
+
+/*
+ * Multiply a 64-bit count by a 64-bit tick 'period' in units of seconds >> 64
+ * and add the fractional second part of the reference time.
+ *
+ * The result is a 128-bit value, the top 64 bits of which are seconds, and
+ * the low 64 bits are (seconds >> 64).
+ */
+static uint64_t mul_u64_u64_shr_add_u64(uint64_t *res_hi, uint64_t delta,
+					uint64_t period, uint8_t shift,
+					uint64_t frac_sec)
+{
+	unsigned __int128 res = (unsigned __int128)delta * period;
+
+	res >>= shift;
+	res += frac_sec;
+	*res_hi = res >> 64;
+	return (uint64_t)res;
+}
+
+static bool tai_adjust(struct vmclock_abi *clk, uint64_t *sec)
+{
+	if (clk->time_type == VMCLOCK_TIME_TAI)
+		return true;
+
+	if (clk->time_type == VMCLOCK_TIME_UTC &&
+	    (le64_to_cpu(clk->flags) & VMCLOCK_FLAG_TAI_OFFSET_VALID)) {
+		if (sec)
+			*sec -= (int16_t)le16_to_cpu(clk->tai_offset_sec);
+		return true;
+	}
+	return false;
+}
+
+static int vmclock_get_crosststamp(struct vmclock_state *st,
+				   struct ptp_system_timestamp *sts,
+				   struct system_counterval_t *system_counter,
+				   struct timespec64 *tspec)
+{
+	ktime_t deadline = ktime_add(ktime_get(), VMCLOCK_MAX_WAIT);
+	uint64_t cycle, delta, seq, frac_sec;
+
+#ifdef CONFIG_X86
+	/*
+	 * We'd expect the hypervisor to know this and to report the clock
+	 * status as VMCLOCK_STATUS_UNRELIABLE. But be paranoid.
+	 */
+	if (check_tsc_unstable())
+		return -EINVAL;
+#endif
+
+	while (1) {
+		seq = le32_to_cpu(st->clk->seq_count) & ~1ULL;
+
+		/*
+		 * This pairs with a write barrier in the hypervisor
+		 * which populates this structure.
+		 */
+		virt_rmb();
+
+		if (st->clk->clock_status == VMCLOCK_STATUS_UNRELIABLE)
+			return -EINVAL;
+
+		/*
+		 * When invoked for gettimex64(), fill in the pre/post system
+		 * times. The simple case is when system time is based on the
+		 * same counter as st->cs_id, in which case all three times
+		 * will be derived from the *same* counter value.
+		 *
+		 * If the system isn't using the same counter, then the value
+		 * from ptp_read_system_prets() will still be used as pre_ts,
+		 * and ptp_read_system_postts() is called to populate postts
+		 * after calling get_cycles().
+		 */
+		if (sts) {
+			ptp_read_system_prets(sts);
+			if (sts->pre_sts.cs_id == st->cs_id) {
+				cycle = sts->pre_sts.cycles;
+				sts->post_sts = sts->pre_sts;
+			} else if (sts->pre_sts.hw_csid == st->cs_id &&
+				   sts->pre_sts.hw_cycles) {
+				cycle = sts->pre_sts.hw_cycles;
+				sts->post_sts = sts->pre_sts;
+			} else {
+				cycle = get_cycles();
+				ptp_read_system_postts(sts);
+			}
+		} else {
+			cycle = get_cycles();
+		}
+
+		delta = cycle - le64_to_cpu(st->clk->counter_value);
+
+		frac_sec = mul_u64_u64_shr_add_u64(&tspec->tv_sec, delta,
+						   le64_to_cpu(st->clk->counter_period_frac_sec),
+						   st->clk->counter_period_shift,
+						   le64_to_cpu(st->clk->time_frac_sec));
+		tspec->tv_nsec = mul_u64_u64_shr(frac_sec, NSEC_PER_SEC, 64);
+		tspec->tv_sec += le64_to_cpu(st->clk->time_sec);
+
+		if (!tai_adjust(st->clk, &tspec->tv_sec))
+			return -EINVAL;
+
+		/*
+		 * This pairs with a write barrier in the hypervisor
+		 * which populates this structure.
+		 */
+		virt_rmb();
+		if (seq == le32_to_cpu(st->clk->seq_count))
+			break;
+
+		if (ktime_after(ktime_get(), deadline))
+			return -ETIMEDOUT;
+	}
+
+	if (system_counter) {
+		system_counter->cycles = cycle;
+		system_counter->cs_id = st->cs_id;
+	}
+
+	return 0;
+}
+
+#ifdef SUPPORT_KVMCLOCK
+/*
+ * In the case where the system is using the KVM clock for timekeeping, convert
+ * the TSC value into a KVM clock time in order to return a paired reading that
+ * get_device_system_crosststamp() can cope with.
+ */
+static int vmclock_get_crosststamp_kvmclock(struct vmclock_state *st,
+					    struct ptp_system_timestamp *sts,
+					    struct system_counterval_t *system_counter,
+					    struct timespec64 *tspec)
+{
+	struct pvclock_vcpu_time_info *pvti = this_cpu_pvti();
+	unsigned int pvti_ver;
+	int ret;
+
+	preempt_disable_notrace();
+
+	do {
+		pvti_ver = pvclock_read_begin(pvti);
+
+		ret = vmclock_get_crosststamp(st, sts, system_counter, tspec);
+		if (ret)
+			break;
+
+		system_counter->cycles = __pvclock_read_cycles(pvti,
+							       system_counter->cycles);
+		system_counter->cs_id = CSID_X86_KVM_CLK;
+
+		/*
+		 * This retry should never really happen; if the TSC is
+		 * stable and reliable enough across vCPUS that it is sane
+		 * for the hypervisor to expose a VMCLOCK device which uses
+		 * it as the reference counter, then the KVM clock sohuld be
+		 * in 'master clock mode' and basically never changed. But
+		 * the KVM clock is a fickle and often broken thing, so do
+		 * it "properly" just in case.
+		 */
+	} while (pvclock_read_retry(pvti, pvti_ver));
+
+	preempt_enable_notrace();
+
+	return ret;
+}
+#endif
+
+static int ptp_vmclock_get_time_fn(ktime_t *device_time,
+				   struct system_counterval_t *system_counter,
+				   void *ctx)
+{
+	struct vmclock_state *st = ctx;
+	struct timespec64 tspec;
+	int ret;
+
+#ifdef SUPPORT_KVMCLOCK
+	if (READ_ONCE(st->sys_cs_id) == CSID_X86_KVM_CLK)
+		ret = vmclock_get_crosststamp_kvmclock(st, NULL, system_counter,
+						       &tspec);
+	else
+#endif
+		ret = vmclock_get_crosststamp(st, NULL, system_counter, &tspec);
+
+	if (!ret)
+		*device_time = timespec64_to_ktime(tspec);
+
+	return ret;
+}
+
+static int ptp_vmclock_getcrosststamp(struct ptp_clock_info *ptp,
+				      struct system_device_crosststamp *xtstamp)
+{
+	struct vmclock_state *st = container_of(ptp, struct vmclock_state,
+						ptp_clock_info);
+	int ret = get_device_system_crosststamp(ptp_vmclock_get_time_fn, st,
+						NULL, xtstamp);
+#ifdef SUPPORT_KVMCLOCK
+	/*
+	 * On x86, the KVM clock may be used for the system time. We can
+	 * actually convert a TSC reading to that, and return a paired
+	 * timestamp that get_device_system_crosststamp() *can* handle.
+	 */
+	if (ret == -ENODEV) {
+		struct system_time_snapshot systime_snapshot;
+
+		ktime_get_snapshot_id(CLOCK_REALTIME, &systime_snapshot);
+
+		if (systime_snapshot.cs_id == CSID_X86_TSC ||
+		    systime_snapshot.cs_id == CSID_X86_KVM_CLK) {
+			WRITE_ONCE(st->sys_cs_id, systime_snapshot.cs_id);
+			ret = get_device_system_crosststamp(ptp_vmclock_get_time_fn,
+							    st, NULL, xtstamp);
+		}
+	}
+#endif
+	return ret;
+}
+
+/*
+ * PTP clock operations
+ */
+
+static int ptp_vmclock_adjfine(struct ptp_clock_info *ptp, long delta)
+{
+	return -EOPNOTSUPP;
+}
+
+static int ptp_vmclock_adjtime(struct ptp_clock_info *ptp, s64 delta)
+{
+	return -EOPNOTSUPP;
+}
+
+static int ptp_vmclock_settime(struct ptp_clock_info *ptp,
+			   const struct timespec64 *ts)
+{
+	return -EOPNOTSUPP;
+}
+
+static int ptp_vmclock_gettimex(struct ptp_clock_info *ptp, struct timespec64 *ts,
+				struct ptp_system_timestamp *sts)
+{
+	struct vmclock_state *st = container_of(ptp, struct vmclock_state,
+						ptp_clock_info);
+
+	return vmclock_get_crosststamp(st, sts, NULL, ts);
+}
+
+static int ptp_vmclock_enable(struct ptp_clock_info *ptp,
+			  struct ptp_clock_request *rq, int on)
+{
+	return -EOPNOTSUPP;
+}
+
+static const struct ptp_clock_info ptp_vmclock_info = {
+	.owner		= THIS_MODULE,
+	.max_adj	= 0,
+	.n_ext_ts	= 0,
+	.n_pins		= 0,
+	.pps		= 0,
+	.adjfine	= ptp_vmclock_adjfine,
+	.adjtime	= ptp_vmclock_adjtime,
+	.gettimex64	= ptp_vmclock_gettimex,
+	.settime64	= ptp_vmclock_settime,
+	.enable		= ptp_vmclock_enable,
+	.getcrosststamp = ptp_vmclock_getcrosststamp,
+};
+
+static struct ptp_clock *vmclock_ptp_register(struct device *dev,
+					      struct vmclock_state *st)
+{
+	enum clocksource_ids cs_id;
+
+	if (IS_ENABLED(CONFIG_ARM64) &&
+	    st->clk->counter_id == VMCLOCK_COUNTER_ARM_VCNT) {
+		/* Can we check it's the virtual counter? */
+		cs_id = CSID_ARM_ARCH_COUNTER;
+	} else if (IS_ENABLED(CONFIG_X86) &&
+		   st->clk->counter_id == VMCLOCK_COUNTER_X86_TSC) {
+		cs_id = CSID_X86_TSC;
+	} else {
+		return NULL;
+	}
+
+	/* Accept TAI directly, or UTC with valid offset for conversion to TAI */
+	if (!tai_adjust(st->clk, NULL)) {
+		dev_info(dev, "vmclock does not provide unambiguous time\n");
+		return NULL;
+	}
+
+	st->sys_cs_id = cs_id;
+	st->cs_id = cs_id;
+	st->ptp_clock_info = ptp_vmclock_info;
+	strscpy(st->ptp_clock_info.name, st->name);
+
+	return ptp_clock_register(&st->ptp_clock_info, dev);
+}
+
+struct vmclock_file_state {
+	struct vmclock_state *st;
+	atomic_t seq;
+};
+
+static int vmclock_miscdev_mmap(struct file *fp, struct vm_area_struct *vma)
+{
+	struct vmclock_file_state *fst = fp->private_data;
+	struct vmclock_state *st = fst->st;
+
+	if ((vma->vm_flags & (VM_READ|VM_WRITE)) != VM_READ)
+		return -EROFS;
+
+	/*
+	 * Restrict the read-only mapping so it cannot be upgraded to
+	 * writable later with mprotect().
+	 */
+	vm_flags_clear(vma, VM_MAYWRITE);
+
+	if (vma->vm_end - vma->vm_start != PAGE_SIZE || vma->vm_pgoff)
+		return -EINVAL;
+
+	if (io_remap_pfn_range(vma, vma->vm_start,
+			       st->res.start >> PAGE_SHIFT, PAGE_SIZE,
+			       vma->vm_page_prot))
+		return -EAGAIN;
+
+	return 0;
+}
+
+static ssize_t vmclock_miscdev_read(struct file *fp, char __user *buf,
+				    size_t count, loff_t *ppos)
+{
+	ktime_t deadline = ktime_add(ktime_get(), VMCLOCK_MAX_WAIT);
+	struct vmclock_file_state *fst = fp->private_data;
+	struct vmclock_state *st = fst->st;
+	uint32_t seq, old_seq;
+	size_t max_count;
+
+	if (*ppos >= PAGE_SIZE)
+		return 0;
+
+	max_count = PAGE_SIZE - *ppos;
+	if (count > max_count)
+		count = max_count;
+
+	old_seq = atomic_read(&fst->seq);
+	while (1) {
+		seq = le32_to_cpu(st->clk->seq_count) & ~1U;
+		/* Pairs with hypervisor wmb */
+		virt_rmb();
+
+		if (copy_to_user(buf, ((char *)st->clk) + *ppos, count))
+			return -EFAULT;
+
+		/* Pairs with hypervisor wmb */
+		virt_rmb();
+		if (seq == le32_to_cpu(st->clk->seq_count)) {
+			/*
+			 * Either we updated fst->seq to seq (the latest version we observed)
+			 * or someone else did (old_seq == seq), so we can break.
+			 */
+			if (atomic_try_cmpxchg(&fst->seq, &old_seq, seq) ||
+			    old_seq == seq) {
+				break;
+			}
+		}
+
+		if (ktime_after(ktime_get(), deadline))
+			return -ETIMEDOUT;
+	}
+
+	*ppos += count;
+	return count;
+}
+
+static __poll_t vmclock_miscdev_poll(struct file *fp, poll_table *wait)
+{
+	struct vmclock_file_state *fst = fp->private_data;
+	struct vmclock_state *st = fst->st;
+	uint32_t seq;
+
+	/*
+	 * Hypervisor will not send us any notifications, so fail immediately
+	 * to avoid having caller sleeping for ever.
+	 */
+	if (!(le64_to_cpu(st->clk->flags) & VMCLOCK_FLAG_NOTIFICATION_PRESENT))
+		return POLLHUP;
+
+	poll_wait(fp, &st->disrupt_wait, wait);
+
+	seq = le32_to_cpu(st->clk->seq_count);
+	if (atomic_read(&fst->seq) != seq)
+		return POLLIN | POLLRDNORM;
+
+	return 0;
+}
+
+static int vmclock_miscdev_open(struct inode *inode, struct file *fp)
+{
+	struct vmclock_state *st = container_of(fp->private_data,
+						struct vmclock_state, miscdev);
+	struct vmclock_file_state *fst = kzalloc_obj(*fst);
+
+	if (!fst)
+		return -ENOMEM;
+
+	fst->st = st;
+	atomic_set(&fst->seq, 0);
+
+	fp->private_data = fst;
+
+	return 0;
+}
+
+static int vmclock_miscdev_release(struct inode *inode, struct file *fp)
+{
+	kfree(fp->private_data);
+	return 0;
+}
+
+static const struct file_operations vmclock_miscdev_fops = {
+	.owner = THIS_MODULE,
+	.open = vmclock_miscdev_open,
+	.release = vmclock_miscdev_release,
+	.mmap = vmclock_miscdev_mmap,
+	.read = vmclock_miscdev_read,
+	.poll = vmclock_miscdev_poll,
+};
+
+/* module operations */
+
+#if IS_ENABLED(CONFIG_ACPI)
+static acpi_status vmclock_acpi_resources(struct acpi_resource *ares, void *data)
+{
+	struct vmclock_state *st = data;
+	struct resource_win win;
+	struct resource *res = &win.res;
+
+	if (ares->type == ACPI_RESOURCE_TYPE_END_TAG)
+		return AE_OK;
+
+	/* There can be only one */
+	if (resource_type(&st->res) == IORESOURCE_MEM)
+		return AE_ERROR;
+
+	if (acpi_dev_resource_memory(ares, res) ||
+	    acpi_dev_resource_address_space(ares, &win)) {
+
+		if (resource_type(res) != IORESOURCE_MEM ||
+		    resource_size(res) < sizeof(st->clk))
+			return AE_ERROR;
+
+		st->res = *res;
+		return AE_OK;
+	}
+
+	return AE_ERROR;
+}
+
+static void
+vmclock_acpi_notification_handler(acpi_handle __always_unused handle,
+				  u32 __always_unused event, void *dev)
+{
+	struct device *device = dev;
+	struct vmclock_state *st = device->driver_data;
+
+	wake_up_interruptible(&st->disrupt_wait);
+}
+
+static int vmclock_setup_acpi_notification(struct device *dev)
+{
+	struct acpi_device *adev = ACPI_COMPANION(dev);
+	acpi_status status;
+
+	/*
+	 * This should never happen as this function is only called when
+	 * has_acpi_companion(dev) is true, but the logic is sufficiently
+	 * complex that Coverity can't see the tautology.
+	 */
+	if (!adev)
+		return -ENODEV;
+
+	status = acpi_install_notify_handler(adev->handle, ACPI_DEVICE_NOTIFY,
+					     vmclock_acpi_notification_handler,
+					     dev);
+	if (ACPI_FAILURE(status)) {
+		dev_err(dev, "failed to install notification handler");
+		return -ENODEV;
+	}
+
+	return 0;
+}
+
+static int vmclock_probe_acpi(struct device *dev, struct vmclock_state *st)
+{
+	struct acpi_device *adev = ACPI_COMPANION(dev);
+	acpi_status status;
+
+	/*
+	 * This should never happen as this function is only called when
+	 * has_acpi_companion(dev) is true, but the logic is sufficiently
+	 * complex that Coverity can't see the tautology.
+	 */
+	if (!adev)
+		return -ENODEV;
+
+	status = acpi_walk_resources(adev->handle, METHOD_NAME__CRS,
+				     vmclock_acpi_resources, st);
+	if (ACPI_FAILURE(status) || resource_type(&st->res) != IORESOURCE_MEM) {
+		dev_err(dev, "failed to get resources\n");
+		return -ENODEV;
+	}
+
+	return 0;
+}
+#endif /* CONFIG_ACPI */
+
+static irqreturn_t vmclock_of_irq_handler(int __always_unused irq, void *_st)
+{
+	struct vmclock_state *st = _st;
+
+	wake_up_interruptible(&st->disrupt_wait);
+	return IRQ_HANDLED;
+}
+
+static int vmclock_probe_dt(struct device *dev, struct vmclock_state *st)
+{
+	struct platform_device *pdev = to_platform_device(dev);
+	struct resource *res;
+
+	res = platform_get_resource(pdev, IORESOURCE_MEM, 0);
+	if (!res)
+		return -ENODEV;
+
+	st->res = *res;
+
+	return 0;
+}
+
+static int vmclock_setup_of_notification(struct device *dev)
+{
+	struct platform_device *pdev = to_platform_device(dev);
+	int irq;
+
+	irq = platform_get_irq(pdev, 0);
+	if (irq < 0)
+		return irq;
+
+	return devm_request_irq(dev, irq, vmclock_of_irq_handler, IRQF_SHARED,
+				"vmclock", dev->driver_data);
+}
+
+static int vmclock_setup_notification(struct device *dev,
+				      struct vmclock_state *st)
+{
+	/* The device does not support notifications. Nothing else to do */
+	if (!(le64_to_cpu(st->clk->flags) & VMCLOCK_FLAG_NOTIFICATION_PRESENT))
+		return 0;
+
+#if IS_ENABLED(CONFIG_ACPI)
+	if (has_acpi_companion(dev))
+		return vmclock_setup_acpi_notification(dev);
+#endif
+	return vmclock_setup_of_notification(dev);
+}
+
+static void vmclock_remove(void *data)
+{
+	struct device *dev = data;
+	struct vmclock_state *st = dev->driver_data;
+
+	if (!st) {
+		dev_err(dev, "%s called with NULL driver_data", __func__);
+		return;
+	}
+
+#if IS_ENABLED(CONFIG_ACPI)
+	if (has_acpi_companion(dev))
+		acpi_remove_notify_handler(ACPI_COMPANION(dev)->handle,
+					   ACPI_DEVICE_NOTIFY,
+					   vmclock_acpi_notification_handler);
+#endif
+
+	if (st->ptp_clock)
+		ptp_clock_unregister(st->ptp_clock);
+
+	if (st->miscdev.minor != MISC_DYNAMIC_MINOR)
+		misc_deregister(&st->miscdev);
+
+	dev->driver_data = NULL;
+}
+
+static void vmclock_put_idx(void *data)
+{
+	struct vmclock_state *st = data;
+
+	ida_free(&vmclock_ida, st->index);
+}
+
+static int vmclock_probe(struct platform_device *pdev)
+{
+	struct device *dev = &pdev->dev;
+	struct vmclock_state *st;
+	int ret;
+
+	st = devm_kzalloc(dev, sizeof(*st), GFP_KERNEL);
+	if (!st)
+		return -ENOMEM;
+
+#if IS_ENABLED(CONFIG_ACPI)
+	if (has_acpi_companion(dev))
+		ret = vmclock_probe_acpi(dev, st);
+	else
+#endif
+		ret = vmclock_probe_dt(dev, st);
+
+	if (ret) {
+		dev_info(dev, "Failed to obtain physical address: %d\n", ret);
+		return ret;
+	}
+
+	if (resource_size(&st->res) < VMCLOCK_MIN_SIZE) {
+		dev_info(dev, "Region too small (0x%llx)\n",
+			 resource_size(&st->res));
+		return -EINVAL;
+	}
+	st->clk = devm_memremap(dev, st->res.start, resource_size(&st->res),
+				MEMREMAP_WB | MEMREMAP_DEC);
+	if (IS_ERR(st->clk)) {
+		ret = PTR_ERR(st->clk);
+		dev_info(dev, "failed to map shared memory\n");
+		st->clk = NULL;
+		return ret;
+	}
+
+	if (le32_to_cpu(st->clk->magic) != VMCLOCK_MAGIC ||
+	    le32_to_cpu(st->clk->size) > resource_size(&st->res) ||
+	    le16_to_cpu(st->clk->version) != 1) {
+		dev_info(dev, "vmclock magic fields invalid\n");
+		return -EINVAL;
+	}
+
+	ret = ida_alloc(&vmclock_ida, GFP_KERNEL);
+	if (ret < 0)
+		return ret;
+
+	st->index = ret;
+	ret = devm_add_action_or_reset(&pdev->dev, vmclock_put_idx, st);
+	if (ret)
+		return ret;
+
+	st->name = devm_kasprintf(&pdev->dev, GFP_KERNEL, "vmclock%d", st->index);
+	if (!st->name)
+		return -ENOMEM;
+
+	st->miscdev.minor = MISC_DYNAMIC_MINOR;
+
+	init_waitqueue_head(&st->disrupt_wait);
+	dev->driver_data = st;
+
+	ret = devm_add_action_or_reset(&pdev->dev, vmclock_remove, dev);
+	if (ret)
+		return ret;
+
+	ret = vmclock_setup_notification(dev, st);
+	if (ret)
+		return ret;
+
+	/*
+	 * If the structure is big enough, it can be mapped to userspace.
+	 * Theoretically a guest OS even using larger pages could still
+	 * use 4KiB PTEs to map smaller MMIO regions like this, but let's
+	 * cross that bridge if/when we come to it.
+	 */
+	if (le32_to_cpu(st->clk->size) >= PAGE_SIZE) {
+		st->miscdev.fops = &vmclock_miscdev_fops;
+		st->miscdev.name = st->name;
+
+		ret = misc_register(&st->miscdev);
+		if (ret)
+			return ret;
+	}
+
+	/* If there is valid clock information, register a PTP clock */
+	if (VMCLOCK_FIELD_PRESENT(st->clk, time_frac_sec)) {
+		/* Can return a silent NULL, or an error. */
+		st->ptp_clock = vmclock_ptp_register(dev, st);
+		if (IS_ERR(st->ptp_clock)) {
+			ret = PTR_ERR(st->ptp_clock);
+			st->ptp_clock = NULL;
+			return ret;
+		}
+	}
+
+	if (!st->miscdev.minor && !st->ptp_clock) {
+		/* Neither miscdev nor PTP registered */
+		dev_info(dev, "vmclock: Neither miscdev nor PTP available; not registering\n");
+		return -ENODEV;
+	}
+
+	dev_info(dev, "%s: registered %s%s%s\n", st->name,
+		 st->miscdev.minor ? "miscdev" : "",
+		 (st->miscdev.minor && st->ptp_clock) ? ", " : "",
+		 st->ptp_clock ? "PTP" : "");
+
+	return 0;
+}
+
+static const struct acpi_device_id vmclock_acpi_ids[] = {
+	{ "AMZNC10C", 0 },
+	{ "VMCLOCK", 0 },
+	{}
+};
+MODULE_DEVICE_TABLE(acpi, vmclock_acpi_ids);
+
+static const struct of_device_id vmclock_of_ids[] = {
+	{ .compatible = "amazon,vmclock", },
+	{ },
+};
+MODULE_DEVICE_TABLE(of, vmclock_of_ids);
+
+static struct platform_driver vmclock_platform_driver = {
+	.probe		= vmclock_probe,
+	.driver	= {
+		.name	= "vmclock",
+		.acpi_match_table = vmclock_acpi_ids,
+		.of_match_table = vmclock_of_ids,
+	},
+};
+
+module_platform_driver(vmclock_platform_driver)
+
+MODULE_AUTHOR("David Woodhouse <dwmw2@infradead.org>");
+MODULE_DESCRIPTION("PTP clock using VMCLOCK");
+MODULE_LICENSE("GPL");