From a5f7a5bb3b7f28ba7e4fa246775b29a0e5537255 Mon Sep 17 00:00:00 2001 From: Jinke Han Date: Tue, 8 Sep 2026 15:37:42 +0800 Subject: x86/kprobes: Fix crash when probing CS CALL instructions 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) Signed-off-by: Jinke Han Signed-off-by: Ingo Molnar Reviewed-by: Masami Hiramatsu (Google) Acked-by: Yafang Shao Acked-by: Borislav Petkov Cc: Peter Zijlstra Link: https://patch.msgid.link/20260908073742.GA10517@didi-ThinkCentre-M920t-N000 --- drivers/char/misc.c | 319 ++++++++++++++++++++++++++++++++++++++++++++++++++++ 1 file changed, 319 insertions(+) create mode 100644 drivers/char/misc.c (limited to 'drivers/char/misc.c') diff --git a/drivers/char/misc.c b/drivers/char/misc.c new file mode 100644 index 000000000..726516fb0 --- /dev/null +++ b/drivers/char/misc.c @@ -0,0 +1,319 @@ +// SPDX-License-Identifier: GPL-2.0 +/* + * linux/drivers/char/misc.c + * + * Generic misc open routine by Johan Myreen + * + * Based on code from Linus + * + * Teemu Rantanen's Microsoft Busmouse support and Derrick Cole's + * changes incorporated into 0.97pl4 + * by Peter Cervasio (pete%q106fm.uucp@wupost.wustl.edu) (08SEP92) + * See busmouse.c for particulars. + * + * Made things a lot mode modular - easy to compile in just one or two + * of the misc drivers, as they are now completely independent. Linus. + * + * Support for loadable modules. 8-Sep-95 Philip Blundell + * + * Fixed a failing symbol register to free the device registration + * Alan Cox 21-Jan-96 + * + * Dynamic minors and /proc/mice by Alessandro Rubini. 26-Mar-96 + * + * Renamed to misc and miscdevice to be more accurate. Alan Cox 26-Mar-96 + * + * Handling of mouse minor numbers for kerneld: + * Idea by Jacques Gelinas , + * adapted by Bjorn Ekwall + * corrected by Alan Cox + * + * Changes for kmod (from kerneld): + * Cyrus Durgin + * + * Added devfs support. Richard Gooch 10-Jan-1998 + */ + +#include + +#include +#include +#include +#include +#include +#include +#include +#include +#include +#include +#include +#include +#include +#include + +/* + * Head entry for the doubly linked miscdevice list + */ +static LIST_HEAD(misc_list); +static DEFINE_MUTEX(misc_mtx); + +/* + * Assigned numbers. + */ +static DEFINE_IDA(misc_minors_ida); + +static int misc_minor_alloc(int minor) +{ + int ret = 0; + + if (minor == MISC_DYNAMIC_MINOR) { + /* allocate free id */ + ret = ida_alloc_range(&misc_minors_ida, MISC_DYNAMIC_MINOR + 1, + MINORMASK, GFP_KERNEL); + } else { + ret = ida_alloc_range(&misc_minors_ida, minor, minor, GFP_KERNEL); + } + return ret; +} + +static void misc_minor_free(int minor) +{ + ida_free(&misc_minors_ida, minor); +} + +#ifdef CONFIG_PROC_FS +static void *misc_seq_start(struct seq_file *seq, loff_t *pos) +{ + mutex_lock(&misc_mtx); + return seq_list_start(&misc_list, *pos); +} + +static void *misc_seq_next(struct seq_file *seq, void *v, loff_t *pos) +{ + return seq_list_next(v, &misc_list, pos); +} + +static void misc_seq_stop(struct seq_file *seq, void *v) +{ + mutex_unlock(&misc_mtx); +} + +static int misc_seq_show(struct seq_file *seq, void *v) +{ + const struct miscdevice *p = list_entry(v, struct miscdevice, list); + + seq_printf(seq, "%3i %s\n", p->minor, p->name ? p->name : ""); + return 0; +} + + +static const struct seq_operations misc_seq_ops = { + .start = misc_seq_start, + .next = misc_seq_next, + .stop = misc_seq_stop, + .show = misc_seq_show, +}; +#endif + +static int misc_open(struct inode *inode, struct file *file) +{ + int minor = iminor(inode); + struct miscdevice *c = NULL, *iter; + int err = -ENODEV; + const struct file_operations *new_fops = NULL; + + mutex_lock(&misc_mtx); + + list_for_each_entry(iter, &misc_list, list) { + if (iter->minor != minor) + continue; + c = iter; + new_fops = fops_get(iter->fops); + break; + } + + /* Only request module for fixed minor code */ + if (!new_fops && minor < MISC_DYNAMIC_MINOR) { + mutex_unlock(&misc_mtx); + request_module("char-major-%d-%d", MISC_MAJOR, minor); + mutex_lock(&misc_mtx); + + list_for_each_entry(iter, &misc_list, list) { + if (iter->minor != minor) + continue; + c = iter; + new_fops = fops_get(iter->fops); + break; + } + } + + if (!new_fops) + goto fail; + + /* + * Place the miscdevice in the file's + * private_data so it can be used by the + * file operations, including f_op->open below + */ + file->private_data = c; + + err = 0; + replace_fops(file, new_fops); + if (file->f_op->open) + err = file->f_op->open(inode, file); +fail: + mutex_unlock(&misc_mtx); + return err; +} + +static char *misc_devnode(const struct device *dev, umode_t *mode) +{ + const struct miscdevice *c = dev_get_drvdata(dev); + + if (mode && c->mode) + *mode = c->mode; + if (c->nodename) + return kstrdup(c->nodename, GFP_KERNEL); + return NULL; +} + +static const struct class misc_class = { + .name = "misc", + .devnode = misc_devnode, +}; + +static const struct file_operations misc_fops = { + .owner = THIS_MODULE, + .open = misc_open, + .llseek = noop_llseek, +}; + +/** + * misc_register - register a miscellaneous device + * @misc: device structure + * + * Register a miscellaneous device with the kernel. If the minor + * number is set to %MISC_DYNAMIC_MINOR a minor number is assigned + * and placed in the minor field of the structure. For other cases + * the minor number requested is used. + * + * The structure passed is linked into the kernel and may not be + * destroyed until it has been unregistered. By default, an open() + * syscall to the device sets file->private_data to point to the + * structure. Drivers don't need open in fops for this. + * + * A zero is returned on success and a negative errno code for + * failure. + */ + +int misc_register(struct miscdevice *misc) +{ + dev_t dev; + int err = 0; + bool is_dynamic = (misc->minor == MISC_DYNAMIC_MINOR); + + if (misc->minor > MISC_DYNAMIC_MINOR) { + pr_err("Invalid fixed minor %d for miscdevice '%s'\n", + misc->minor, misc->name); + return -EINVAL; + } + + INIT_LIST_HEAD(&misc->list); + + mutex_lock(&misc_mtx); + + if (is_dynamic) { + int i = misc_minor_alloc(misc->minor); + + if (i < 0) { + err = -EBUSY; + goto out; + } + misc->minor = i; + } else { + struct miscdevice *c; + int i; + + list_for_each_entry(c, &misc_list, list) { + if (c->minor == misc->minor) { + err = -EBUSY; + goto out; + } + } + + i = misc_minor_alloc(misc->minor); + if (i < 0) { + err = -EBUSY; + goto out; + } + } + + dev = MKDEV(MISC_MAJOR, misc->minor); + + misc->this_device = + device_create_with_groups(&misc_class, misc->parent, dev, + misc, misc->groups, "%s", misc->name); + if (IS_ERR(misc->this_device)) { + misc_minor_free(misc->minor); + if (is_dynamic) { + misc->minor = MISC_DYNAMIC_MINOR; + } + err = PTR_ERR(misc->this_device); + goto out; + } + + /* + * Add it to the front, so that later devices can "override" + * earlier defaults + */ + list_add(&misc->list, &misc_list); + out: + mutex_unlock(&misc_mtx); + return err; +} +EXPORT_SYMBOL(misc_register); + +/** + * misc_deregister - unregister a miscellaneous device + * @misc: device to unregister + * + * Unregister a miscellaneous device that was previously + * successfully registered with misc_register(). + */ + +void misc_deregister(struct miscdevice *misc) +{ + mutex_lock(&misc_mtx); + list_del_init(&misc->list); + device_destroy(&misc_class, MKDEV(MISC_MAJOR, misc->minor)); + misc_minor_free(misc->minor); + if (misc->minor > MISC_DYNAMIC_MINOR) + misc->minor = MISC_DYNAMIC_MINOR; + mutex_unlock(&misc_mtx); +} +EXPORT_SYMBOL(misc_deregister); + +static int __init misc_init(void) +{ + int err; + struct proc_dir_entry *misc_proc_file; + + misc_proc_file = proc_create_seq("misc", 0, NULL, &misc_seq_ops); + err = class_register(&misc_class); + if (err) + goto fail_remove; + + err = __register_chrdev(MISC_MAJOR, 0, MINORMASK + 1, "misc", &misc_fops); + if (err < 0) + goto fail_printk; + return 0; + +fail_printk: + pr_err("unable to get major %d for misc devices\n", MISC_MAJOR); + class_unregister(&misc_class); +fail_remove: + if (misc_proc_file) + remove_proc_entry("misc", NULL); + return err; +} +subsys_initcall(misc_init); -- cgit v1.3.1