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 --- fs/init.c | 218 ++++++++++++++++++++++++++++++++++++++++++++++++++++++++++++++ 1 file changed, 218 insertions(+) create mode 100644 fs/init.c (limited to 'fs/init.c') diff --git a/fs/init.c b/fs/init.c new file mode 100644 index 000000000..33e312d74 --- /dev/null +++ b/fs/init.c @@ -0,0 +1,218 @@ +// SPDX-License-Identifier: GPL-2.0 +/* + * Routines that mimic syscalls, but don't use the user address space or file + * descriptors. Only for init/ and related early init code. + */ +#include +#include +#include +#include +#include +#include +#include +#include +#include "internal.h" + +int __init init_pivot_root(const char *new_root, const char *put_old) +{ + struct path new_path __free(path_put) = {}; + struct path old_path __free(path_put) = {}; + int ret; + + ret = kern_path(new_root, LOOKUP_FOLLOW | LOOKUP_DIRECTORY, &new_path); + if (ret) + return ret; + + ret = kern_path(put_old, LOOKUP_FOLLOW | LOOKUP_DIRECTORY, &old_path); + if (ret) + return ret; + + return path_pivot_root(&new_path, &old_path); +} + +int __init init_mount(const char *dev_name, const char *dir_name, + const char *type_page, unsigned long flags, void *data_page) +{ + struct path path; + int ret; + + ret = kern_path(dir_name, LOOKUP_FOLLOW, &path); + if (ret) + return ret; + ret = path_mount(dev_name, &path, type_page, flags, data_page); + path_put(&path); + return ret; +} + +int __init init_umount(const char *name, int flags) +{ + int lookup_flags = LOOKUP_MOUNTPOINT; + struct path path; + int ret; + + if (!(flags & UMOUNT_NOFOLLOW)) + lookup_flags |= LOOKUP_FOLLOW; + ret = kern_path(name, lookup_flags, &path); + if (ret) + return ret; + return path_umount(&path, flags); +} + +int __init init_chdir(const char *filename) +{ + struct path path; + int error; + + error = kern_path(filename, LOOKUP_FOLLOW | LOOKUP_DIRECTORY, &path); + if (error) + return error; + error = path_permission(&path, MAY_EXEC | MAY_CHDIR); + if (!error) + set_fs_pwd(current->fs, &path); + path_put(&path); + return error; +} + +int __init init_chroot(const char *filename) +{ + struct path path; + int error; + + error = kern_path(filename, LOOKUP_FOLLOW | LOOKUP_DIRECTORY, &path); + if (error) + return error; + error = path_permission(&path, MAY_EXEC | MAY_CHDIR); + if (error) + goto dput_and_out; + error = -EPERM; + if (!ns_capable(current_user_ns(), CAP_SYS_CHROOT)) + goto dput_and_out; + error = security_path_chroot(&path); + if (error) + goto dput_and_out; + set_fs_root(current->fs, &path); +dput_and_out: + path_put(&path); + return error; +} + +int __init init_chown(const char *filename, uid_t user, gid_t group, int flags) +{ + int lookup_flags = (flags & AT_SYMLINK_NOFOLLOW) ? 0 : LOOKUP_FOLLOW; + struct path path; + int error; + + error = kern_path(filename, lookup_flags, &path); + if (error) + return error; + error = mnt_want_write(path.mnt); + if (!error) { + error = chown_common(&path, user, group); + mnt_drop_write(path.mnt); + } + path_put(&path); + return error; +} + +int __init init_chmod(const char *filename, umode_t mode) +{ + struct path path; + int error; + + error = kern_path(filename, LOOKUP_FOLLOW, &path); + if (error) + return error; + error = chmod_common(&path, mode); + path_put(&path); + return error; +} + +int __init init_eaccess(const char *filename) +{ + struct path path; + int error; + + error = kern_path(filename, LOOKUP_FOLLOW, &path); + if (error) + return error; + error = path_permission(&path, MAY_ACCESS); + path_put(&path); + return error; +} + +int __init init_stat(const char *filename, struct kstat *stat, int flags) +{ + int lookup_flags = (flags & AT_SYMLINK_NOFOLLOW) ? 0 : LOOKUP_FOLLOW; + struct path path; + int error; + + error = kern_path(filename, lookup_flags, &path); + if (error) + return error; + error = vfs_getattr(&path, stat, STATX_BASIC_STATS, + flags | AT_NO_AUTOMOUNT); + path_put(&path); + return error; +} + +int __init init_mknod(const char *filename, umode_t mode, unsigned int dev) +{ + CLASS(filename_kernel, name)(filename); + return filename_mknodat(AT_FDCWD, name, mode, dev); +} + +int __init init_link(const char *oldname, const char *newname) +{ + CLASS(filename_kernel, old)(oldname); + CLASS(filename_kernel, new)(newname); + return filename_linkat(AT_FDCWD, old, AT_FDCWD, new, 0); +} + +int __init init_symlink(const char *oldname, const char *newname) +{ + CLASS(filename_kernel, old)(oldname); + CLASS(filename_kernel, new)(newname); + return filename_symlinkat(old, AT_FDCWD, new); +} + +int __init init_unlink(const char *pathname) +{ + CLASS(filename_kernel, name)(pathname); + return filename_unlinkat(AT_FDCWD, name); +} + +int __init init_mkdir(const char *pathname, umode_t mode) +{ + CLASS(filename_kernel, name)(pathname); + return filename_mkdirat(AT_FDCWD, name, mode); +} + +int __init init_rmdir(const char *pathname) +{ + CLASS(filename_kernel, name)(pathname); + return filename_rmdir(AT_FDCWD, name); +} + +int __init init_utimes(char *filename, struct timespec64 *ts) +{ + struct path path; + int error; + + error = kern_path(filename, 0, &path); + if (error) + return error; + error = vfs_utimes(&path, ts); + path_put(&path); + return error; +} + +int __init init_dup(struct file *file) +{ + int fd; + + fd = get_unused_fd_flags(0); + if (fd < 0) + return fd; + fd_install(fd, get_file(file)); + return 0; +} -- cgit v1.3.1