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/anon_inodes.c | 358 +++++++++++++++++++++++++++++++++++++++++++++++++++++++ 1 file changed, 358 insertions(+) create mode 100644 fs/anon_inodes.c (limited to 'fs/anon_inodes.c') diff --git a/fs/anon_inodes.c b/fs/anon_inodes.c new file mode 100644 index 000000000..a7b9b948e --- /dev/null +++ b/fs/anon_inodes.c @@ -0,0 +1,358 @@ +// SPDX-License-Identifier: GPL-2.0-only +/* + * fs/anon_inodes.c + * + * Copyright (C) 2007 Davide Libenzi + * + * Thanks to Arnd Bergmann for code review and suggestions. + * More changes for Thomas Gleixner suggestions. + * + */ + +#include +#include +#include +#include +#include +#include +#include +#include +#include +#include +#include +#include + +#include + +#include "internal.h" + +static struct vfsmount *anon_inode_mnt __ro_after_init; +static struct inode *anon_inode_inode __ro_after_init; + +/* + * User space expects anonymous inodes to have no file type in st_mode. + * + * In particular, 'lsof' has this legacy logic: + * + * type = s->st_mode & S_IFMT; + * switch (type) { + * ... + * case 0: + * if (!strcmp(p, "anon_inode")) + * Lf->ntype = Ntype = N_ANON_INODE; + * + * to detect our old anon_inode logic. + * + * Rather than mess with our internal sane inode data, just fix it + * up here in getattr() by masking off the format bits. + */ +int anon_inode_getattr(struct mnt_idmap *idmap, const struct path *path, + struct kstat *stat, u32 request_mask, + unsigned int query_flags) +{ + struct inode *inode = d_inode(path->dentry); + + generic_fillattr(&nop_mnt_idmap, request_mask, inode, stat); + stat->mode &= ~S_IFMT; + return 0; +} + +int anon_inode_setattr(struct mnt_idmap *idmap, struct dentry *dentry, + struct iattr *attr) +{ + return -EOPNOTSUPP; +} + +static const struct inode_operations anon_inode_operations = { + .getattr = anon_inode_getattr, + .setattr = anon_inode_setattr, +}; + +/* + * anon_inodefs_dname() is called from d_path(). + */ +static char *anon_inodefs_dname(struct dentry *dentry, char *buffer, int buflen) +{ + return dynamic_dname(buffer, buflen, "anon_inode:%s", + dentry->d_name.name); +} + +static const struct dentry_operations anon_inodefs_dentry_operations = { + .d_dname = anon_inodefs_dname, +}; + +static int anon_inodefs_init_fs_context(struct fs_context *fc) +{ + struct pseudo_fs_context *ctx = init_pseudo(fc, ANON_INODE_FS_MAGIC); + if (!ctx) + return -ENOMEM; + ctx->dops = &anon_inodefs_dentry_operations; + return 0; +} + +static struct file_system_type anon_inode_fs_type = { + .name = "anon_inodefs", + .init_fs_context = anon_inodefs_init_fs_context, + .kill_sb = kill_anon_super, +}; + +/** + * anon_inode_make_secure_inode - allocate an anonymous inode with security context + * @sb: [in] Superblock to allocate from + * @name: [in] Name of the class of the newfile (e.g., "secretmem") + * @context_inode: + * [in] Optional parent inode for security inheritance + * + * The function ensures proper security initialization through the LSM hook + * security_inode_init_security_anon(). + * + * Return: Pointer to new inode on success, ERR_PTR on failure. + */ +struct inode *anon_inode_make_secure_inode(struct super_block *sb, const char *name, + const struct inode *context_inode) +{ + struct inode *inode; + int error; + + inode = alloc_anon_inode(sb); + if (IS_ERR(inode)) + return inode; + inode->i_flags &= ~S_PRIVATE; + inode->i_op = &anon_inode_operations; + error = security_inode_init_security_anon(inode, &QSTR(name), + context_inode); + if (error) { + iput(inode); + return ERR_PTR(error); + } + return inode; +} +EXPORT_SYMBOL_FOR_MODULES(anon_inode_make_secure_inode, "kvm"); + +static struct file *__anon_inode_getfile(const char *name, + const struct file_operations *fops, + void *priv, int flags, + const struct inode *context_inode, + bool make_inode) +{ + struct inode *inode; + struct file *file; + + if (fops->owner && !try_module_get(fops->owner)) + return ERR_PTR(-ENOENT); + + if (make_inode) { + inode = anon_inode_make_secure_inode(anon_inode_mnt->mnt_sb, + name, context_inode); + if (IS_ERR(inode)) { + file = ERR_CAST(inode); + goto err; + } + } else { + inode = anon_inode_inode; + if (IS_ERR(inode)) { + file = ERR_PTR(-ENODEV); + goto err; + } + /* + * We know the anon_inode inode count is always + * greater than zero, so ihold() is safe. + */ + ihold(inode); + } + + file = alloc_file_pseudo(inode, anon_inode_mnt, name, + flags & (O_ACCMODE | O_NONBLOCK), fops); + if (IS_ERR(file)) + goto err_iput; + + file->f_mapping = inode->i_mapping; + + file->private_data = priv; + + return file; + +err_iput: + iput(inode); +err: + module_put(fops->owner); + return file; +} + +/** + * anon_inode_getfile - creates a new file instance by hooking it up to an + * anonymous inode, and a dentry that describe the "class" + * of the file + * + * @name: [in] name of the "class" of the new file + * @fops: [in] file operations for the new file + * @priv: [in] private data for the new file (will be file's private_data) + * @flags: [in] flags + * + * Creates a new file by hooking it on a single inode. This is useful for files + * that do not need to have a full-fledged inode in order to operate correctly. + * All the files created with anon_inode_getfile() will share a single inode, + * hence saving memory and avoiding code duplication for the file/inode/dentry + * setup. Returns the newly created file* or an error pointer. + */ +struct file *anon_inode_getfile(const char *name, + const struct file_operations *fops, + void *priv, int flags) +{ + return __anon_inode_getfile(name, fops, priv, flags, NULL, false); +} +EXPORT_SYMBOL_GPL(anon_inode_getfile); + +/** + * anon_inode_getfile_fmode - creates a new file instance by hooking it up to an + * anonymous inode, and a dentry that describe the "class" + * of the file + * + * @name: [in] name of the "class" of the new file + * @fops: [in] file operations for the new file + * @priv: [in] private data for the new file (will be file's private_data) + * @flags: [in] flags + * @f_mode: [in] fmode + * + * Creates a new file by hooking it on a single inode. This is useful for files + * that do not need to have a full-fledged inode in order to operate correctly. + * All the files created with anon_inode_getfile() will share a single inode, + * hence saving memory and avoiding code duplication for the file/inode/dentry + * setup. Allows setting the fmode. Returns the newly created file* or an error + * pointer. + */ +struct file *anon_inode_getfile_fmode(const char *name, + const struct file_operations *fops, + void *priv, int flags, fmode_t f_mode) +{ + struct file *file; + + file = __anon_inode_getfile(name, fops, priv, flags, NULL, false); + if (!IS_ERR(file)) + file->f_mode |= f_mode; + + return file; +} +EXPORT_SYMBOL_GPL(anon_inode_getfile_fmode); + +/** + * anon_inode_create_getfile - Like anon_inode_getfile(), but creates a new + * !S_PRIVATE anon inode rather than reuse the + * singleton anon inode and calls the + * inode_init_security_anon() LSM hook. + * + * @name: [in] name of the "class" of the new file + * @fops: [in] file operations for the new file + * @priv: [in] private data for the new file (will be file's private_data) + * @flags: [in] flags + * @context_inode: + * [in] the logical relationship with the new inode (optional) + * + * Create a new anonymous inode and file pair. This can be done for two + * reasons: + * + * - for the inode to have its own security context, so that LSMs can enforce + * policy on the inode's creation; + * + * - if the caller needs a unique inode, for example in order to customize + * the size returned by fstat() + * + * The LSM may use @context_inode in inode_init_security_anon(), but a + * reference to it is not held. + * + * Returns the newly created file* or an error pointer. + */ +struct file *anon_inode_create_getfile(const char *name, + const struct file_operations *fops, + void *priv, int flags, + const struct inode *context_inode) +{ + return __anon_inode_getfile(name, fops, priv, flags, + context_inode, true); +} +EXPORT_SYMBOL_GPL(anon_inode_create_getfile); + +static int __anon_inode_getfd(const char *name, + const struct file_operations *fops, + void *priv, int flags, + const struct inode *context_inode, + bool make_inode) +{ + return FD_ADD(flags, __anon_inode_getfile(name, fops, priv, flags, + context_inode, make_inode)); +} + +/** + * anon_inode_getfd - creates a new file instance by hooking it up to + * an anonymous inode and a dentry that describe + * the "class" of the file + * + * @name: [in] name of the "class" of the new file + * @fops: [in] file operations for the new file + * @priv: [in] private data for the new file (will be file's private_data) + * @flags: [in] flags + * + * Creates a new file by hooking it on a single inode. This is + * useful for files that do not need to have a full-fledged inode in + * order to operate correctly. All the files created with + * anon_inode_getfd() will use the same singleton inode, reducing + * memory use and avoiding code duplication for the file/inode/dentry + * setup. Returns a newly created file descriptor or an error code. + */ +int anon_inode_getfd(const char *name, const struct file_operations *fops, + void *priv, int flags) +{ + return __anon_inode_getfd(name, fops, priv, flags, NULL, false); +} +EXPORT_SYMBOL_GPL(anon_inode_getfd); + +/** + * anon_inode_create_getfd - Like anon_inode_getfd(), but creates a new + * !S_PRIVATE anon inode rather than reuse the singleton anon inode, and calls + * the inode_init_security_anon() LSM hook. + * + * @name: [in] name of the "class" of the new file + * @fops: [in] file operations for the new file + * @priv: [in] private data for the new file (will be file's private_data) + * @flags: [in] flags + * @context_inode: + * [in] the logical relationship with the new inode (optional) + * + * Create a new anonymous inode and file pair. This can be done for two + * reasons: + * + * - for the inode to have its own security context, so that LSMs can enforce + * policy on the inode's creation; + * + * - if the caller needs a unique inode, for example in order to customize + * the size returned by fstat() + * + * The LSM may use @context_inode in inode_init_security_anon(), but a + * reference to it is not held. + * + * Returns a newly created file descriptor or an error code. + */ +int anon_inode_create_getfd(const char *name, const struct file_operations *fops, + void *priv, int flags, + const struct inode *context_inode) +{ + return __anon_inode_getfd(name, fops, priv, flags, context_inode, true); +} + + +static int __init anon_inode_init(void) +{ + anon_inode_mnt = kern_mount(&anon_inode_fs_type); + if (IS_ERR(anon_inode_mnt)) + panic("anon_inode_init() kernel mount failed (%ld)\n", PTR_ERR(anon_inode_mnt)); + + anon_inode_inode = alloc_anon_inode(anon_inode_mnt->mnt_sb); + if (IS_ERR(anon_inode_inode)) + panic("anon_inode_init() inode allocation failed (%ld)\n", PTR_ERR(anon_inode_inode)); + anon_inode_inode->i_op = &anon_inode_operations; + + return 0; +} + +fs_initcall(anon_inode_init); + -- cgit v1.3.1