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, 623 insertions, 0 deletions

diff --git a/drivers/misc/ocxl/file.c b/drivers/misc/ocxl/file.c
new file mode 100644
index 000000000..1abbde33e
--- /dev/null
+++ b/drivers/misc/ocxl/file.c
@@ -0,0 +1,623 @@
+// SPDX-License-Identifier: GPL-2.0+
+// Copyright 2017 IBM Corp.
+#include <linux/fs.h>
+#include <linux/poll.h>
+#include <linux/sched/signal.h>
+#include <linux/eventfd.h>
+#include <linux/uaccess.h>
+#include <uapi/misc/ocxl.h>
+#include <asm/reg.h>
+#include <asm/switch_to.h>
+#include "ocxl_internal.h"
+
+
+#define OCXL_NUM_MINORS 256 /* Total to reserve */
+
+static dev_t ocxl_dev;
+static DEFINE_MUTEX(minors_idr_lock);
+static struct idr minors_idr;
+
+static struct ocxl_file_info *find_and_get_file_info(dev_t devno)
+{
+	struct ocxl_file_info *info;
+
+	mutex_lock(&minors_idr_lock);
+	info = idr_find(&minors_idr, MINOR(devno));
+	if (info)
+		get_device(&info->dev);
+	mutex_unlock(&minors_idr_lock);
+	return info;
+}
+
+static int allocate_minor(struct ocxl_file_info *info)
+{
+	int minor;
+
+	mutex_lock(&minors_idr_lock);
+	minor = idr_alloc(&minors_idr, info, 0, OCXL_NUM_MINORS, GFP_KERNEL);
+	mutex_unlock(&minors_idr_lock);
+	return minor;
+}
+
+static void free_minor(struct ocxl_file_info *info)
+{
+	mutex_lock(&minors_idr_lock);
+	idr_remove(&minors_idr, MINOR(info->dev.devt));
+	mutex_unlock(&minors_idr_lock);
+}
+
+static int afu_open(struct inode *inode, struct file *file)
+{
+	struct ocxl_file_info *info;
+	struct ocxl_context *ctx;
+	int rc;
+
+	pr_debug("%s for device %x\n", __func__, inode->i_rdev);
+
+	info = find_and_get_file_info(inode->i_rdev);
+	if (!info)
+		return -ENODEV;
+
+	rc = ocxl_context_alloc(&ctx, info->afu, inode->i_mapping);
+	if (rc) {
+		put_device(&info->dev);
+		return rc;
+	}
+	put_device(&info->dev);
+	file->private_data = ctx;
+	return 0;
+}
+
+static long afu_ioctl_attach(struct ocxl_context *ctx,
+			struct ocxl_ioctl_attach __user *uarg)
+{
+	struct ocxl_ioctl_attach arg;
+	u64 amr = 0;
+
+	pr_debug("%s for context %d\n", __func__, ctx->pasid);
+
+	if (copy_from_user(&arg, uarg, sizeof(arg)))
+		return -EFAULT;
+
+	/* Make sure reserved fields are not set for forward compatibility */
+	if (arg.reserved1 || arg.reserved2 || arg.reserved3)
+		return -EINVAL;
+
+	amr = arg.amr & mfspr(SPRN_UAMOR);
+	return ocxl_context_attach(ctx, amr, current->mm);
+}
+
+static long afu_ioctl_get_metadata(struct ocxl_context *ctx,
+		struct ocxl_ioctl_metadata __user *uarg)
+{
+	struct ocxl_ioctl_metadata arg;
+
+	memset(&arg, 0, sizeof(arg));
+
+	arg.version = 0;
+
+	arg.afu_version_major = ctx->afu->config.version_major;
+	arg.afu_version_minor = ctx->afu->config.version_minor;
+	arg.pasid = ctx->pasid;
+	arg.pp_mmio_size = ctx->afu->config.pp_mmio_stride;
+	arg.global_mmio_size = ctx->afu->config.global_mmio_size;
+
+	if (copy_to_user(uarg, &arg, sizeof(arg)))
+		return -EFAULT;
+
+	return 0;
+}
+
+#ifdef CONFIG_PPC64
+static long afu_ioctl_enable_p9_wait(struct ocxl_context *ctx,
+		struct ocxl_ioctl_p9_wait __user *uarg)
+{
+	struct ocxl_ioctl_p9_wait arg;
+
+	memset(&arg, 0, sizeof(arg));
+
+	if (cpu_has_feature(CPU_FTR_P9_TIDR)) {
+		enum ocxl_context_status status;
+
+		// Locks both status & tidr
+		mutex_lock(&ctx->status_mutex);
+		if (!ctx->tidr) {
+			if (set_thread_tidr(current)) {
+				mutex_unlock(&ctx->status_mutex);
+				return -ENOENT;
+			}
+
+			ctx->tidr = current->thread.tidr;
+		}
+
+		status = ctx->status;
+		mutex_unlock(&ctx->status_mutex);
+
+		if (status == ATTACHED) {
+			int rc = ocxl_link_update_pe(ctx->afu->fn->link,
+				ctx->pasid, ctx->tidr);
+
+			if (rc)
+				return rc;
+		}
+
+		arg.thread_id = ctx->tidr;
+	} else
+		return -ENOENT;
+
+	if (copy_to_user(uarg, &arg, sizeof(arg)))
+		return -EFAULT;
+
+	return 0;
+}
+#endif
+
+
+static long afu_ioctl_get_features(struct ocxl_context *ctx,
+		struct ocxl_ioctl_features __user *uarg)
+{
+	struct ocxl_ioctl_features arg;
+
+	memset(&arg, 0, sizeof(arg));
+
+#ifdef CONFIG_PPC64
+	if (cpu_has_feature(CPU_FTR_P9_TIDR))
+		arg.flags[0] |= OCXL_IOCTL_FEATURES_FLAGS0_P9_WAIT;
+#endif
+
+	if (copy_to_user(uarg, &arg, sizeof(arg)))
+		return -EFAULT;
+
+	return 0;
+}
+
+#define CMD_STR(x) (x == OCXL_IOCTL_ATTACH ? "ATTACH" :			\
+			x == OCXL_IOCTL_IRQ_ALLOC ? "IRQ_ALLOC" :	\
+			x == OCXL_IOCTL_IRQ_FREE ? "IRQ_FREE" :		\
+			x == OCXL_IOCTL_IRQ_SET_FD ? "IRQ_SET_FD" :	\
+			x == OCXL_IOCTL_GET_METADATA ? "GET_METADATA" :	\
+			x == OCXL_IOCTL_ENABLE_P9_WAIT ? "ENABLE_P9_WAIT" :	\
+			x == OCXL_IOCTL_GET_FEATURES ? "GET_FEATURES" :	\
+			"UNKNOWN")
+
+static irqreturn_t irq_handler(void *private)
+{
+	struct eventfd_ctx *ev_ctx = private;
+
+	eventfd_signal(ev_ctx);
+	return IRQ_HANDLED;
+}
+
+static void irq_free(void *private)
+{
+	struct eventfd_ctx *ev_ctx = private;
+
+	eventfd_ctx_put(ev_ctx);
+}
+
+static long afu_ioctl(struct file *file, unsigned int cmd,
+		unsigned long args)
+{
+	struct ocxl_context *ctx = file->private_data;
+	struct ocxl_ioctl_irq_fd irq_fd;
+	struct eventfd_ctx *ev_ctx;
+	int irq_id;
+	u64 irq_offset;
+	long rc;
+	bool closed;
+
+	pr_debug("%s for context %d, command %s\n", __func__, ctx->pasid,
+		CMD_STR(cmd));
+
+	mutex_lock(&ctx->status_mutex);
+	closed = (ctx->status == CLOSED);
+	mutex_unlock(&ctx->status_mutex);
+
+	if (closed)
+		return -EIO;
+
+	switch (cmd) {
+	case OCXL_IOCTL_ATTACH:
+		rc = afu_ioctl_attach(ctx,
+				(struct ocxl_ioctl_attach __user *) args);
+		break;
+
+	case OCXL_IOCTL_IRQ_ALLOC:
+		rc = ocxl_afu_irq_alloc(ctx, &irq_id);
+		if (!rc) {
+			irq_offset = ocxl_irq_id_to_offset(ctx, irq_id);
+			rc = copy_to_user((u64 __user *) args, &irq_offset,
+					sizeof(irq_offset));
+			if (rc) {
+				ocxl_afu_irq_free(ctx, irq_id);
+				return -EFAULT;
+			}
+		}
+		break;
+
+	case OCXL_IOCTL_IRQ_FREE:
+		rc = copy_from_user(&irq_offset, (u64 __user *) args,
+				sizeof(irq_offset));
+		if (rc)
+			return -EFAULT;
+		irq_id = ocxl_irq_offset_to_id(ctx, irq_offset);
+		rc = ocxl_afu_irq_free(ctx, irq_id);
+		break;
+
+	case OCXL_IOCTL_IRQ_SET_FD:
+		rc = copy_from_user(&irq_fd, (u64 __user *) args,
+				sizeof(irq_fd));
+		if (rc)
+			return -EFAULT;
+		if (irq_fd.reserved)
+			return -EINVAL;
+		irq_id = ocxl_irq_offset_to_id(ctx, irq_fd.irq_offset);
+		ev_ctx = eventfd_ctx_fdget(irq_fd.eventfd);
+		if (IS_ERR(ev_ctx))
+			return PTR_ERR(ev_ctx);
+		rc = ocxl_irq_set_handler(ctx, irq_id, irq_handler, irq_free, ev_ctx);
+		if (rc)
+			eventfd_ctx_put(ev_ctx);
+		break;
+
+	case OCXL_IOCTL_GET_METADATA:
+		rc = afu_ioctl_get_metadata(ctx,
+				(struct ocxl_ioctl_metadata __user *) args);
+		break;
+
+#ifdef CONFIG_PPC64
+	case OCXL_IOCTL_ENABLE_P9_WAIT:
+		rc = afu_ioctl_enable_p9_wait(ctx,
+				(struct ocxl_ioctl_p9_wait __user *) args);
+		break;
+#endif
+
+	case OCXL_IOCTL_GET_FEATURES:
+		rc = afu_ioctl_get_features(ctx,
+				(struct ocxl_ioctl_features __user *) args);
+		break;
+
+	default:
+		rc = -EINVAL;
+	}
+	return rc;
+}
+
+static long afu_compat_ioctl(struct file *file, unsigned int cmd,
+			unsigned long args)
+{
+	return afu_ioctl(file, cmd, args);
+}
+
+static int afu_mmap(struct file *file, struct vm_area_struct *vma)
+{
+	struct ocxl_context *ctx = file->private_data;
+
+	pr_debug("%s for context %d\n", __func__, ctx->pasid);
+	return ocxl_context_mmap(ctx, vma);
+}
+
+static bool has_xsl_error(struct ocxl_context *ctx)
+{
+	bool ret;
+
+	mutex_lock(&ctx->xsl_error_lock);
+	ret = !!ctx->xsl_error.addr;
+	mutex_unlock(&ctx->xsl_error_lock);
+
+	return ret;
+}
+
+/*
+ * Are there any events pending on the AFU
+ * ctx: The AFU context
+ * Returns: true if there are events pending
+ */
+static bool afu_events_pending(struct ocxl_context *ctx)
+{
+	if (has_xsl_error(ctx))
+		return true;
+	return false;
+}
+
+static unsigned int afu_poll(struct file *file, struct poll_table_struct *wait)
+{
+	struct ocxl_context *ctx = file->private_data;
+	unsigned int mask = 0;
+	bool closed;
+
+	pr_debug("%s for context %d\n", __func__, ctx->pasid);
+
+	poll_wait(file, &ctx->events_wq, wait);
+
+	mutex_lock(&ctx->status_mutex);
+	closed = (ctx->status == CLOSED);
+	mutex_unlock(&ctx->status_mutex);
+
+	if (afu_events_pending(ctx))
+		mask = EPOLLIN | EPOLLRDNORM;
+	else if (closed)
+		mask = EPOLLERR;
+
+	return mask;
+}
+
+/*
+ * Populate the supplied buffer with a single XSL error
+ * ctx:	The AFU context to report the error from
+ * header: the event header to populate
+ * buf: The buffer to write the body into (should be at least
+ *      AFU_EVENT_BODY_XSL_ERROR_SIZE)
+ * Return: the amount of buffer that was populated
+ */
+static ssize_t append_xsl_error(struct ocxl_context *ctx,
+				struct ocxl_kernel_event_header *header,
+				char __user *buf)
+{
+	struct ocxl_kernel_event_xsl_fault_error body;
+
+	memset(&body, 0, sizeof(body));
+
+	mutex_lock(&ctx->xsl_error_lock);
+	if (!ctx->xsl_error.addr) {
+		mutex_unlock(&ctx->xsl_error_lock);
+		return 0;
+	}
+
+	body.addr = ctx->xsl_error.addr;
+	body.dsisr = ctx->xsl_error.dsisr;
+	body.count = ctx->xsl_error.count;
+
+	ctx->xsl_error.addr = 0;
+	ctx->xsl_error.dsisr = 0;
+	ctx->xsl_error.count = 0;
+
+	mutex_unlock(&ctx->xsl_error_lock);
+
+	header->type = OCXL_AFU_EVENT_XSL_FAULT_ERROR;
+
+	if (copy_to_user(buf, &body, sizeof(body)))
+		return -EFAULT;
+
+	return sizeof(body);
+}
+
+#define AFU_EVENT_BODY_MAX_SIZE sizeof(struct ocxl_kernel_event_xsl_fault_error)
+
+/*
+ * Reports events on the AFU
+ * Format:
+ *	Header (struct ocxl_kernel_event_header)
+ *	Body (struct ocxl_kernel_event_*)
+ *	Header...
+ */
+static ssize_t afu_read(struct file *file, char __user *buf, size_t count,
+			loff_t *off)
+{
+	struct ocxl_context *ctx = file->private_data;
+	struct ocxl_kernel_event_header header;
+	ssize_t rc;
+	ssize_t used = 0;
+	DEFINE_WAIT(event_wait);
+
+	memset(&header, 0, sizeof(header));
+
+	/* Require offset to be 0 */
+	if (*off != 0)
+		return -EINVAL;
+
+	if (count < (sizeof(struct ocxl_kernel_event_header) +
+			AFU_EVENT_BODY_MAX_SIZE))
+		return -EINVAL;
+
+	for (;;) {
+		prepare_to_wait(&ctx->events_wq, &event_wait,
+				TASK_INTERRUPTIBLE);
+
+		if (afu_events_pending(ctx))
+			break;
+
+		if (ctx->status == CLOSED)
+			break;
+
+		if (file->f_flags & O_NONBLOCK) {
+			finish_wait(&ctx->events_wq, &event_wait);
+			return -EAGAIN;
+		}
+
+		if (signal_pending(current)) {
+			finish_wait(&ctx->events_wq, &event_wait);
+			return -ERESTARTSYS;
+		}
+
+		schedule();
+	}
+
+	finish_wait(&ctx->events_wq, &event_wait);
+
+	if (has_xsl_error(ctx)) {
+		used = append_xsl_error(ctx, &header, buf + sizeof(header));
+		if (used < 0)
+			return used;
+	}
+
+	if (!afu_events_pending(ctx))
+		header.flags |= OCXL_KERNEL_EVENT_FLAG_LAST;
+
+	if (copy_to_user(buf, &header, sizeof(header)))
+		return -EFAULT;
+
+	used += sizeof(header);
+
+	rc = used;
+	return rc;
+}
+
+static int afu_release(struct inode *inode, struct file *file)
+{
+	struct ocxl_context *ctx = file->private_data;
+	int rc;
+
+	pr_debug("%s for device %x\n", __func__, inode->i_rdev);
+	rc = ocxl_context_detach(ctx);
+	mutex_lock(&ctx->mapping_lock);
+	ctx->mapping = NULL;
+	mutex_unlock(&ctx->mapping_lock);
+	wake_up_all(&ctx->events_wq);
+	if (rc != -EBUSY)
+		ocxl_context_free(ctx);
+	return 0;
+}
+
+static const struct file_operations ocxl_afu_fops = {
+	.owner		= THIS_MODULE,
+	.open           = afu_open,
+	.unlocked_ioctl = afu_ioctl,
+	.compat_ioctl   = afu_compat_ioctl,
+	.mmap           = afu_mmap,
+	.poll           = afu_poll,
+	.read           = afu_read,
+	.release        = afu_release,
+};
+
+// Free the info struct
+static void info_release(struct device *dev)
+{
+	struct ocxl_file_info *info = container_of(dev, struct ocxl_file_info, dev);
+
+	ocxl_afu_put(info->afu);
+	kfree(info);
+}
+
+static int ocxl_file_make_visible(struct ocxl_file_info *info)
+{
+	int rc;
+
+	cdev_init(&info->cdev, &ocxl_afu_fops);
+	rc = cdev_add(&info->cdev, info->dev.devt, 1);
+	if (rc) {
+		dev_err(&info->dev, "Unable to add afu char device: %d\n", rc);
+		return rc;
+	}
+
+	return 0;
+}
+
+static void ocxl_file_make_invisible(struct ocxl_file_info *info)
+{
+	cdev_del(&info->cdev);
+}
+
+static char *ocxl_devnode(const struct device *dev, umode_t *mode)
+{
+	return kasprintf(GFP_KERNEL, "ocxl/%s", dev_name(dev));
+}
+
+static const struct class ocxl_class = {
+	.name =		"ocxl",
+	.devnode =	ocxl_devnode,
+};
+
+int ocxl_file_register_afu(struct ocxl_afu *afu)
+{
+	int minor;
+	int rc;
+	struct ocxl_file_info *info;
+	struct ocxl_fn *fn = afu->fn;
+	struct pci_dev *pci_dev = to_pci_dev(fn->dev.parent);
+
+	info = kzalloc_obj(*info);
+	if (info == NULL)
+		return -ENOMEM;
+
+	minor = allocate_minor(info);
+	if (minor < 0) {
+		kfree(info);
+		return minor;
+	}
+
+	info->dev.parent = &fn->dev;
+	info->dev.devt = MKDEV(MAJOR(ocxl_dev), minor);
+	info->dev.class = &ocxl_class;
+	info->dev.release = info_release;
+
+	info->afu = afu;
+	ocxl_afu_get(afu);
+
+	rc = dev_set_name(&info->dev, "%s.%s.%hhu",
+		afu->config.name, dev_name(&pci_dev->dev), afu->config.idx);
+	if (rc)
+		goto err_put;
+
+	rc = device_register(&info->dev);
+	if (rc) {
+		free_minor(info);
+		put_device(&info->dev);
+		return rc;
+	}
+
+	rc = ocxl_sysfs_register_afu(info);
+	if (rc)
+		goto err_unregister;
+
+	rc = ocxl_file_make_visible(info);
+	if (rc)
+		goto err_unregister;
+
+	ocxl_afu_set_private(afu, info);
+
+	return 0;
+
+err_unregister:
+	ocxl_sysfs_unregister_afu(info); // safe to call even if register failed
+	free_minor(info);
+	device_unregister(&info->dev);
+	return rc;
+err_put:
+	ocxl_afu_put(afu);
+	free_minor(info);
+	kfree(info);
+	return rc;
+}
+
+void ocxl_file_unregister_afu(struct ocxl_afu *afu)
+{
+	struct ocxl_file_info *info = ocxl_afu_get_private(afu);
+
+	if (!info)
+		return;
+
+	ocxl_file_make_invisible(info);
+	ocxl_sysfs_unregister_afu(info);
+	free_minor(info);
+	device_unregister(&info->dev);
+}
+
+int ocxl_file_init(void)
+{
+	int rc;
+
+	idr_init(&minors_idr);
+
+	rc = alloc_chrdev_region(&ocxl_dev, 0, OCXL_NUM_MINORS, "ocxl");
+	if (rc) {
+		pr_err("Unable to allocate ocxl major number: %d\n", rc);
+		return rc;
+	}
+
+	rc = class_register(&ocxl_class);
+	if (rc) {
+		pr_err("Unable to create ocxl class\n");
+		unregister_chrdev_region(ocxl_dev, OCXL_NUM_MINORS);
+		return rc;
+	}
+
+	return 0;
+}
+
+void ocxl_file_exit(void)
+{
+	class_unregister(&ocxl_class);
+	unregister_chrdev_region(ocxl_dev, OCXL_NUM_MINORS);
+	idr_destroy(&minors_idr);
+}