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, 208 insertions, 0 deletions

diff --git a/drivers/accel/drm_accel.c b/drivers/accel/drm_accel.c
new file mode 100644
index 000000000..ca3357acd
--- /dev/null
+++ b/drivers/accel/drm_accel.c
@@ -0,0 +1,208 @@
+// SPDX-License-Identifier: GPL-2.0
+
+/*
+ * Copyright 2022 HabanaLabs, Ltd.
+ * All Rights Reserved.
+ *
+ */
+
+#include <linux/debugfs.h>
+#include <linux/device.h>
+#include <linux/xarray.h>
+
+#include <drm/drm_accel.h>
+#include <drm/drm_auth.h>
+#include <drm/drm_debugfs.h>
+#include <drm/drm_drv.h>
+#include <drm/drm_file.h>
+#include <drm/drm_ioctl.h>
+#include <drm/drm_print.h>
+
+DEFINE_XARRAY_ALLOC(accel_minors_xa);
+
+static const struct device_type accel_sysfs_device_minor = {
+	.name = "accel_minor"
+};
+
+static char *accel_devnode(const struct device *dev, umode_t *mode)
+{
+	return kasprintf(GFP_KERNEL, "accel/%s", dev_name(dev));
+}
+
+static const struct class accel_class = {
+	.name = "accel",
+	.devnode = accel_devnode,
+};
+
+static int accel_sysfs_init(void)
+{
+	return class_register(&accel_class);
+}
+
+static void accel_sysfs_destroy(void)
+{
+	class_unregister(&accel_class);
+}
+
+static int accel_name_info(struct seq_file *m, void *data)
+{
+	struct drm_info_node *node = (struct drm_info_node *) m->private;
+	struct drm_minor *minor = node->minor;
+	struct drm_device *dev = minor->dev;
+	struct drm_master *master;
+
+	mutex_lock(&dev->master_mutex);
+	master = dev->master;
+	seq_printf(m, "%s", dev->driver->name);
+	if (dev->dev)
+		seq_printf(m, " dev=%s", dev_name(dev->dev));
+	if (master && master->unique)
+		seq_printf(m, " master=%s", master->unique);
+	if (dev->unique)
+		seq_printf(m, " unique=%s", dev->unique);
+	seq_puts(m, "\n");
+	mutex_unlock(&dev->master_mutex);
+
+	return 0;
+}
+
+static const struct drm_info_list accel_debugfs_list[] = {
+	{"name", accel_name_info, 0}
+};
+#define ACCEL_DEBUGFS_ENTRIES ARRAY_SIZE(accel_debugfs_list)
+
+/**
+ * accel_debugfs_register() - Register debugfs for device
+ * @dev: Pointer to the device instance.
+ *
+ * Creates common files for accelerators.
+ */
+void accel_debugfs_register(struct drm_device *dev)
+{
+	struct drm_minor *minor = dev->accel;
+
+	minor->debugfs_root = dev->debugfs_root;
+
+	drm_debugfs_create_files(accel_debugfs_list, ACCEL_DEBUGFS_ENTRIES,
+				 dev->debugfs_root, minor);
+}
+
+/**
+ * accel_set_device_instance_params() - Set some device parameters for accel device
+ * @kdev: Pointer to the device instance.
+ * @index: The minor's index
+ *
+ * This function creates the dev_t of the device using the accel major and
+ * the device's minor number. In addition, it sets the class and type of the
+ * device instance to the accel sysfs class and device type, respectively.
+ */
+void accel_set_device_instance_params(struct device *kdev, int index)
+{
+	kdev->devt = MKDEV(ACCEL_MAJOR, index);
+	kdev->class = &accel_class;
+	kdev->type = &accel_sysfs_device_minor;
+}
+
+/**
+ * accel_open - open method for ACCEL file
+ * @inode: device inode
+ * @filp: file pointer.
+ *
+ * This function must be used by drivers as their &file_operations.open method.
+ * It looks up the correct ACCEL device and instantiates all the per-file
+ * resources for it. It also calls the &drm_driver.open driver callback.
+ *
+ * Return: 0 on success or negative errno value on failure.
+ */
+int accel_open(struct inode *inode, struct file *filp)
+{
+	struct drm_device *dev;
+	struct drm_minor *minor;
+	int retcode;
+
+	minor = drm_minor_acquire(&accel_minors_xa, iminor(inode));
+	if (IS_ERR(minor))
+		return PTR_ERR(minor);
+
+	dev = minor->dev;
+
+	atomic_fetch_inc(&dev->open_count);
+
+	/* share address_space across all char-devs of a single device */
+	filp->f_mapping = dev->anon_inode->i_mapping;
+
+	retcode = drm_open_helper(filp, minor);
+	if (retcode)
+		goto err_undo;
+
+	return 0;
+
+err_undo:
+	atomic_dec(&dev->open_count);
+	drm_minor_release(minor);
+	return retcode;
+}
+EXPORT_SYMBOL_GPL(accel_open);
+
+static int accel_stub_open(struct inode *inode, struct file *filp)
+{
+	const struct file_operations *new_fops;
+	struct drm_minor *minor;
+	int err;
+
+	minor = drm_minor_acquire(&accel_minors_xa, iminor(inode));
+	if (IS_ERR(minor))
+		return PTR_ERR(minor);
+
+	new_fops = fops_get(minor->dev->driver->fops);
+	if (!new_fops) {
+		err = -ENODEV;
+		goto out;
+	}
+
+	replace_fops(filp, new_fops);
+	if (filp->f_op->open)
+		err = filp->f_op->open(inode, filp);
+	else
+		err = 0;
+
+out:
+	drm_minor_release(minor);
+
+	return err;
+}
+
+static const struct file_operations accel_stub_fops = {
+	.owner = THIS_MODULE,
+	.open = accel_stub_open,
+	.llseek = noop_llseek,
+};
+
+void accel_core_exit(void)
+{
+	unregister_chrdev(ACCEL_MAJOR, "accel");
+	accel_sysfs_destroy();
+	WARN_ON(!xa_empty(&accel_minors_xa));
+}
+
+int __init accel_core_init(void)
+{
+	int ret;
+
+	ret = accel_sysfs_init();
+	if (ret < 0) {
+		DRM_ERROR("Cannot create ACCEL class: %d\n", ret);
+		goto error;
+	}
+
+	ret = register_chrdev(ACCEL_MAJOR, "accel", &accel_stub_fops);
+	if (ret < 0)
+		DRM_ERROR("Cannot register ACCEL major: %d\n", ret);
+
+error:
+	/*
+	 * Any cleanup due to errors will be done in drm_core_exit() that
+	 * will call accel_core_exit()
+	 */
+	return ret;
+}