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, 291 insertions, 0 deletions

diff --git a/fs/minix/namei.c b/fs/minix/namei.c
new file mode 100644
index 000000000..5525ba367
--- /dev/null
+++ b/fs/minix/namei.c
@@ -0,0 +1,291 @@
+// SPDX-License-Identifier: GPL-2.0
+/*
+ *  linux/fs/minix/namei.c
+ *
+ *  Copyright (C) 1991, 1992  Linus Torvalds
+ */
+
+#include "minix.h"
+
+static int add_nondir(struct dentry *dentry, struct inode *inode)
+{
+	int err = minix_add_link(dentry, inode);
+	if (!err) {
+		d_instantiate(dentry, inode);
+		return 0;
+	}
+	inode_dec_link_count(inode);
+	iput(inode);
+	return err;
+}
+
+static struct dentry *minix_lookup(struct inode * dir, struct dentry *dentry, unsigned int flags)
+{
+	struct inode * inode = NULL;
+	ino_t ino;
+
+	if (dentry->d_name.len > minix_sb(dir->i_sb)->s_namelen)
+		return ERR_PTR(-ENAMETOOLONG);
+
+	ino = minix_inode_by_name(dentry);
+	if (ino)
+		inode = minix_iget(dir->i_sb, ino);
+	return d_splice_alias(inode, dentry);
+}
+
+static int minix_mknod(struct mnt_idmap *idmap, struct inode *dir,
+		       struct dentry *dentry, umode_t mode, dev_t rdev)
+{
+	struct inode *inode;
+
+	if (!old_valid_dev(rdev))
+		return -EINVAL;
+
+	inode = minix_new_inode(dir, mode);
+	if (IS_ERR(inode))
+		return PTR_ERR(inode);
+
+	minix_set_inode(inode, rdev);
+	mark_inode_dirty(inode);
+	return add_nondir(dentry, inode);
+}
+
+static int minix_tmpfile(struct mnt_idmap *idmap, struct inode *dir,
+			 struct file *file, umode_t mode)
+{
+	struct inode *inode = minix_new_inode(dir, mode);
+
+	if (IS_ERR(inode))
+		return finish_open_simple(file, PTR_ERR(inode));
+	minix_set_inode(inode, 0);
+	mark_inode_dirty(inode);
+	d_tmpfile(file, inode);
+	return finish_open_simple(file, 0);
+}
+
+static int minix_create(struct mnt_idmap *idmap, struct inode *dir,
+			struct dentry *dentry, umode_t mode)
+{
+	return minix_mknod(&nop_mnt_idmap, dir, dentry, mode, 0);
+}
+
+static int minix_symlink(struct mnt_idmap *idmap, struct inode *dir,
+			 struct dentry *dentry, const char *symname)
+{
+	int i = strlen(symname)+1;
+	struct inode * inode;
+	int err;
+
+	if (i > dir->i_sb->s_blocksize)
+		return -ENAMETOOLONG;
+
+	inode = minix_new_inode(dir, S_IFLNK | 0777);
+	if (IS_ERR(inode))
+		return PTR_ERR(inode);
+
+	minix_set_inode(inode, 0);
+	err = page_symlink(inode, symname, i);
+	if (unlikely(err)) {
+		inode_dec_link_count(inode);
+		iput(inode);
+		return err;
+	}
+	return add_nondir(dentry, inode);
+}
+
+static int minix_link(struct dentry * old_dentry, struct inode * dir,
+	struct dentry *dentry)
+{
+	struct inode *inode = d_inode(old_dentry);
+
+	inode_set_ctime_current(inode);
+	inode_inc_link_count(inode);
+	ihold(inode);
+	return add_nondir(dentry, inode);
+}
+
+static struct dentry *minix_mkdir(struct mnt_idmap *idmap, struct inode *dir,
+				  struct dentry *dentry, umode_t mode)
+{
+	struct inode * inode;
+	int err;
+
+	inode = minix_new_inode(dir, mode);
+	if (IS_ERR(inode))
+		return ERR_CAST(inode);
+
+	inode_inc_link_count(dir);
+	minix_set_inode(inode, 0);
+	inode_inc_link_count(inode);
+
+	err = minix_make_empty(inode, dir);
+	if (err)
+		goto out_fail;
+
+	err = minix_add_link(dentry, inode);
+	if (err)
+		goto out_fail;
+
+	d_instantiate(dentry, inode);
+out:
+	return ERR_PTR(err);
+
+out_fail:
+	inode_dec_link_count(inode);
+	inode_dec_link_count(inode);
+	iput(inode);
+	inode_dec_link_count(dir);
+	goto out;
+}
+
+static int minix_unlink(struct inode * dir, struct dentry *dentry)
+{
+	struct inode * inode = d_inode(dentry);
+	struct folio *folio;
+	struct minix_dir_entry * de;
+	int err;
+
+	if (inode->i_nlink == 0) {
+		minix_error_inode(inode, "inode has corrupted nlink");
+		return -EFSCORRUPTED;
+	}
+
+	de = minix_find_entry(dentry, &folio);
+	if (!de)
+		return -ENOENT;
+	err = minix_delete_entry(de, folio);
+	folio_release_kmap(folio, de);
+
+	if (err)
+		return err;
+	inode_set_ctime_to_ts(inode, inode_get_ctime(dir));
+	inode_dec_link_count(inode);
+	return 0;
+}
+
+static int minix_rmdir(struct inode * dir, struct dentry *dentry)
+{
+	struct inode * inode = d_inode(dentry);
+	int err = -EFSCORRUPTED;
+
+	if (dir->i_nlink <= 2) {
+		minix_error_inode(dir, "inode has corrupted nlink");
+		goto out;
+	}
+
+	err = -ENOTEMPTY;
+	if (!minix_empty_dir(inode))
+		goto out;
+
+	err = minix_unlink(dir, dentry);
+	if (!err) {
+		inode_dec_link_count(dir);
+		inode_dec_link_count(inode);
+	}
+
+out:
+	return err;
+}
+
+static int minix_rename(struct mnt_idmap *idmap,
+			struct inode *old_dir, struct dentry *old_dentry,
+			struct inode *new_dir, struct dentry *new_dentry,
+			unsigned int flags)
+{
+	struct inode * old_inode = d_inode(old_dentry);
+	struct inode * new_inode = d_inode(new_dentry);
+	struct folio * dir_folio = NULL;
+	struct minix_dir_entry * dir_de = NULL;
+	struct folio *old_folio;
+	struct minix_dir_entry * old_de;
+	int err = -ENOENT;
+
+	if (flags & ~RENAME_NOREPLACE)
+		return -EINVAL;
+
+	old_de = minix_find_entry(old_dentry, &old_folio);
+	if (!old_de)
+		goto out;
+
+	if (S_ISDIR(old_inode->i_mode)) {
+		err = -EIO;
+		dir_de = minix_dotdot(old_inode, &dir_folio);
+		if (!dir_de)
+			goto out_old;
+	}
+
+	if (new_inode) {
+		struct folio *new_folio;
+		struct minix_dir_entry * new_de;
+
+		err = -ENOTEMPTY;
+		if (dir_de && !minix_empty_dir(new_inode))
+			goto out_dir;
+
+		err = -EFSCORRUPTED;
+		if (new_inode->i_nlink == 0 || (dir_de && new_inode->i_nlink != 2)) {
+			minix_error_inode(new_inode, "inode has corrupted nlink");
+			goto out_dir;
+		}
+
+		if (dir_de && old_dir->i_nlink <= 2) {
+			minix_error_inode(old_dir, "inode has corrupted nlink");
+			goto out_dir;
+		}
+
+		err = -ENOENT;
+		new_de = minix_find_entry(new_dentry, &new_folio);
+		if (!new_de)
+			goto out_dir;
+		err = minix_set_link(new_de, new_folio, old_inode);
+		folio_release_kmap(new_folio, new_de);
+		if (err)
+			goto out_dir;
+		inode_set_ctime_current(new_inode);
+		if (dir_de)
+			drop_nlink(new_inode);
+		inode_dec_link_count(new_inode);
+	} else {
+		err = minix_add_link(new_dentry, old_inode);
+		if (err)
+			goto out_dir;
+		if (dir_de)
+			inode_inc_link_count(new_dir);
+	}
+
+	err = minix_delete_entry(old_de, old_folio);
+	if (err)
+		goto out_dir;
+
+	mark_inode_dirty(old_inode);
+
+	if (dir_de) {
+		err = minix_set_link(dir_de, dir_folio, new_dir);
+		if (!err)
+			inode_dec_link_count(old_dir);
+	}
+out_dir:
+	if (dir_de)
+		folio_release_kmap(dir_folio, dir_de);
+out_old:
+	folio_release_kmap(old_folio, old_de);
+out:
+	return err;
+}
+
+/*
+ * directories can handle most operations...
+ */
+const struct inode_operations minix_dir_inode_operations = {
+	.create		= minix_create,
+	.lookup		= minix_lookup,
+	.link		= minix_link,
+	.unlink		= minix_unlink,
+	.symlink	= minix_symlink,
+	.mkdir		= minix_mkdir,
+	.rmdir		= minix_rmdir,
+	.mknod		= minix_mknod,
+	.rename		= minix_rename,
+	.getattr	= minix_getattr,
+	.tmpfile	= minix_tmpfile,
+};