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, 582 insertions, 0 deletions

diff --git a/fs/affs/namei.c b/fs/affs/namei.c
new file mode 100644
index 000000000..6cb52efaf
--- /dev/null
+++ b/fs/affs/namei.c
@@ -0,0 +1,582 @@
+// SPDX-License-Identifier: GPL-2.0
+/*
+ *  linux/fs/affs/namei.c
+ *
+ *  (c) 1996  Hans-Joachim Widmaier - Rewritten
+ *
+ *  (C) 1993  Ray Burr - Modified for Amiga FFS filesystem.
+ *
+ *  (C) 1991  Linus Torvalds - minix filesystem
+ */
+
+#include "affs.h"
+#include <linux/exportfs.h>
+
+typedef int (*toupper_t)(int);
+
+/* Simple toupper() for DOS\1 */
+
+static int
+affs_toupper(int ch)
+{
+	return ch >= 'a' && ch <= 'z' ? ch -= ('a' - 'A') : ch;
+}
+
+/* International toupper() for DOS\3 ("international") */
+
+static int
+affs_intl_toupper(int ch)
+{
+	return (ch >= 'a' && ch <= 'z') || (ch >= 0xE0
+		&& ch <= 0xFE && ch != 0xF7) ?
+		ch - ('a' - 'A') : ch;
+}
+
+static inline toupper_t
+affs_get_toupper(struct super_block *sb)
+{
+	return affs_test_opt(AFFS_SB(sb)->s_flags, SF_INTL) ?
+	       affs_intl_toupper : affs_toupper;
+}
+
+/*
+ * Note: the dentry argument is the parent dentry.
+ */
+static inline int
+__affs_hash_dentry(const struct dentry *dentry, struct qstr *qstr, toupper_t fn, bool notruncate)
+{
+	const u8 *name = qstr->name;
+	unsigned long hash;
+	int retval;
+	u32 len;
+
+	retval = affs_check_name(qstr->name, qstr->len, notruncate);
+	if (retval)
+		return retval;
+
+	hash = init_name_hash(dentry);
+	len = min(qstr->len, AFFSNAMEMAX);
+	for (; len > 0; name++, len--)
+		hash = partial_name_hash(fn(*name), hash);
+	qstr->hash = end_name_hash(hash);
+
+	return 0;
+}
+
+static int
+affs_hash_dentry(const struct dentry *dentry, struct qstr *qstr)
+{
+	return __affs_hash_dentry(dentry, qstr, affs_toupper,
+				  affs_nofilenametruncate(dentry));
+
+}
+
+static int
+affs_intl_hash_dentry(const struct dentry *dentry, struct qstr *qstr)
+{
+	return __affs_hash_dentry(dentry, qstr, affs_intl_toupper,
+				  affs_nofilenametruncate(dentry));
+
+}
+
+static inline int __affs_compare_dentry(unsigned int len,
+		const char *str, const struct qstr *name, toupper_t fn,
+		bool notruncate)
+{
+	const u8 *aname = str;
+	const u8 *bname = name->name;
+
+	/*
+	 * 'str' is the name of an already existing dentry, so the name
+	 * must be valid. 'name' must be validated first.
+	 */
+
+	if (affs_check_name(name->name, name->len, notruncate))
+		return 1;
+
+	/*
+	 * If the names are longer than the allowed 30 chars,
+	 * the excess is ignored, so their length may differ.
+	 */
+	if (len >= AFFSNAMEMAX) {
+		if (name->len < AFFSNAMEMAX)
+			return 1;
+		len = AFFSNAMEMAX;
+	} else if (len != name->len)
+		return 1;
+
+	for (; len > 0; len--)
+		if (fn(*aname++) != fn(*bname++))
+			return 1;
+
+	return 0;
+}
+
+static int
+affs_compare_dentry(const struct dentry *dentry,
+		unsigned int len, const char *str, const struct qstr *name)
+{
+
+	return __affs_compare_dentry(len, str, name, affs_toupper,
+				     affs_nofilenametruncate(dentry));
+}
+
+static int
+affs_intl_compare_dentry(const struct dentry *dentry,
+		unsigned int len, const char *str, const struct qstr *name)
+{
+	return __affs_compare_dentry(len, str, name, affs_intl_toupper,
+				     affs_nofilenametruncate(dentry));
+
+}
+
+/*
+ * NOTE! unlike strncmp, affs_match returns 1 for success, 0 for failure.
+ */
+
+static inline int
+affs_match(struct dentry *dentry, const u8 *name2, toupper_t fn)
+{
+	const u8 *name = dentry->d_name.name;
+	int len = dentry->d_name.len;
+
+	if (len >= AFFSNAMEMAX) {
+		if (*name2 < AFFSNAMEMAX)
+			return 0;
+		len = AFFSNAMEMAX;
+	} else if (len != *name2)
+		return 0;
+
+	for (name2++; len > 0; len--)
+		if (fn(*name++) != fn(*name2++))
+			return 0;
+	return 1;
+}
+
+int
+affs_hash_name(struct super_block *sb, const u8 *name, unsigned int len)
+{
+	toupper_t fn = affs_get_toupper(sb);
+	u32 hash;
+
+	hash = len = min(len, AFFSNAMEMAX);
+	for (; len > 0; len--)
+		hash = (hash * 13 + fn(*name++)) & 0x7ff;
+
+	return hash % AFFS_SB(sb)->s_hashsize;
+}
+
+static struct buffer_head *
+affs_find_entry(struct inode *dir, struct dentry *dentry)
+{
+	struct super_block *sb = dir->i_sb;
+	struct buffer_head *bh;
+	toupper_t fn = affs_get_toupper(sb);
+	u32 key;
+
+	pr_debug("%s(\"%pd\")\n", __func__, dentry);
+
+	bh = affs_bread(sb, dir->i_ino);
+	if (!bh)
+		return ERR_PTR(-EIO);
+
+	key = be32_to_cpu(AFFS_HEAD(bh)->table[affs_hash_name(sb, dentry->d_name.name, dentry->d_name.len)]);
+
+	for (;;) {
+		affs_brelse(bh);
+		if (key == 0)
+			return NULL;
+		bh = affs_bread(sb, key);
+		if (!bh)
+			return ERR_PTR(-EIO);
+		if (affs_match(dentry, AFFS_TAIL(sb, bh)->name, fn))
+			return bh;
+		key = be32_to_cpu(AFFS_TAIL(sb, bh)->hash_chain);
+	}
+}
+
+struct dentry *
+affs_lookup(struct inode *dir, struct dentry *dentry, unsigned int flags)
+{
+	struct super_block *sb = dir->i_sb;
+	struct buffer_head *bh;
+	struct inode *inode = NULL;
+	struct dentry *res;
+
+	pr_debug("%s(\"%pd\")\n", __func__, dentry);
+
+	affs_lock_dir(dir);
+	bh = affs_find_entry(dir, dentry);
+	if (IS_ERR(bh)) {
+		affs_unlock_dir(dir);
+		return ERR_CAST(bh);
+	}
+	if (bh) {
+		u32 ino = bh->b_blocknr;
+
+		/* store the real header ino in d_fsdata for faster lookups */
+		dentry->d_fsdata = (void *)(long)ino;
+		switch (be32_to_cpu(AFFS_TAIL(sb, bh)->stype)) {
+		//link to dirs disabled
+		//case ST_LINKDIR:
+		case ST_LINKFILE:
+			ino = be32_to_cpu(AFFS_TAIL(sb, bh)->original);
+		}
+		affs_brelse(bh);
+		inode = affs_iget(sb, ino);
+	}
+	res = d_splice_alias(inode, dentry);
+	if (!IS_ERR_OR_NULL(res))
+		res->d_fsdata = dentry->d_fsdata;
+	affs_unlock_dir(dir);
+	return res;
+}
+
+int
+affs_unlink(struct inode *dir, struct dentry *dentry)
+{
+	pr_debug("%s(dir=%llu, %llu \"%pd\")\n", __func__, dir->i_ino,
+		 d_inode(dentry)->i_ino, dentry);
+
+	return affs_remove_header(dentry);
+}
+
+int
+affs_create(struct mnt_idmap *idmap, struct inode *dir,
+	    struct dentry *dentry, umode_t mode)
+{
+	struct super_block *sb = dir->i_sb;
+	struct inode	*inode;
+	int		 error;
+
+	pr_debug("%s(%llu,\"%pd\",0%ho)\n",
+		 __func__, dir->i_ino, dentry, mode);
+
+	inode = affs_new_inode(dir);
+	if (!inode)
+		return -ENOSPC;
+
+	inode->i_mode = mode;
+	affs_mode_to_prot(inode);
+	mark_inode_dirty(inode);
+
+	inode->i_op = &affs_file_inode_operations;
+	inode->i_fop = &affs_file_operations;
+	inode->i_mapping->a_ops = affs_test_opt(AFFS_SB(sb)->s_flags, SF_OFS) ?
+				  &affs_aops_ofs : &affs_aops;
+	error = affs_add_entry(dir, inode, dentry, ST_FILE);
+	if (error) {
+		clear_nlink(inode);
+		iput(inode);
+		return error;
+	}
+	return 0;
+}
+
+struct dentry *
+affs_mkdir(struct mnt_idmap *idmap, struct inode *dir,
+	   struct dentry *dentry, umode_t mode)
+{
+	struct inode		*inode;
+	int			 error;
+
+	pr_debug("%s(%llu,\"%pd\",0%ho)\n",
+		 __func__, dir->i_ino, dentry, mode);
+
+	inode = affs_new_inode(dir);
+	if (!inode)
+		return ERR_PTR(-ENOSPC);
+
+	inode->i_mode = mode;
+	affs_mode_to_prot(inode);
+
+	inode->i_op = &affs_dir_inode_operations;
+	inode->i_fop = &affs_dir_operations;
+
+	error = affs_add_entry(dir, inode, dentry, ST_USERDIR);
+	if (error) {
+		clear_nlink(inode);
+		mark_inode_dirty(inode);
+		iput(inode);
+		return ERR_PTR(error);
+	}
+	return NULL;
+}
+
+int
+affs_rmdir(struct inode *dir, struct dentry *dentry)
+{
+	pr_debug("%s(dir=%llu, %llu \"%pd\")\n", __func__, dir->i_ino,
+		 d_inode(dentry)->i_ino, dentry);
+
+	return affs_remove_header(dentry);
+}
+
+int
+affs_symlink(struct mnt_idmap *idmap, struct inode *dir,
+	     struct dentry *dentry, const char *symname)
+{
+	struct super_block	*sb = dir->i_sb;
+	struct buffer_head	*bh;
+	struct inode		*inode;
+	char			*p;
+	int			 i, maxlen, error;
+	char			 c, lc;
+
+	pr_debug("%s(%llu,\"%pd\" -> \"%s\")\n",
+		 __func__, dir->i_ino, dentry, symname);
+
+	maxlen = AFFS_SB(sb)->s_hashsize * sizeof(u32) - 1;
+	inode  = affs_new_inode(dir);
+	if (!inode)
+		return -ENOSPC;
+
+	inode->i_op = &affs_symlink_inode_operations;
+	inode_nohighmem(inode);
+	inode->i_data.a_ops = &affs_symlink_aops;
+	inode->i_mode = S_IFLNK | 0777;
+	affs_mode_to_prot(inode);
+
+	error = -EIO;
+	bh = affs_bread(sb, inode->i_ino);
+	if (!bh)
+		goto err;
+	i  = 0;
+	p  = (char *)AFFS_HEAD(bh)->table;
+	lc = '/';
+	if (*symname == '/') {
+		struct affs_sb_info *sbi = AFFS_SB(sb);
+		while (*symname == '/')
+			symname++;
+		spin_lock(&sbi->symlink_lock);
+		while (sbi->s_volume[i])	/* Cannot overflow */
+			*p++ = sbi->s_volume[i++];
+		spin_unlock(&sbi->symlink_lock);
+	}
+	while (i < maxlen && (c = *symname++)) {
+		if (c == '.' && lc == '/' && *symname == '.' && symname[1] == '/') {
+			*p++ = '/';
+			i++;
+			symname += 2;
+			lc = '/';
+		} else if (c == '.' && lc == '/' && *symname == '/') {
+			symname++;
+			lc = '/';
+		} else {
+			*p++ = c;
+			lc   = c;
+			i++;
+		}
+		if (lc == '/')
+			while (*symname == '/')
+				symname++;
+	}
+	*p = 0;
+	inode->i_size = i + 1;
+	mark_buffer_dirty(bh);
+	affs_brelse(bh);
+	mark_inode_dirty(inode);
+
+	error = affs_add_entry(dir, inode, dentry, ST_SOFTLINK);
+	if (error)
+		goto err;
+
+	return 0;
+
+err:
+	clear_nlink(inode);
+	mark_inode_dirty(inode);
+	iput(inode);
+	return error;
+}
+
+int
+affs_link(struct dentry *old_dentry, struct inode *dir, struct dentry *dentry)
+{
+	struct inode *inode = d_inode(old_dentry);
+
+	pr_debug("%s(%llu, %llu, \"%pd\")\n", __func__, inode->i_ino, dir->i_ino,
+		 dentry);
+
+	return affs_add_entry(dir, inode, dentry, ST_LINKFILE);
+}
+
+static int
+affs_rename(struct inode *old_dir, struct dentry *old_dentry,
+	    struct inode *new_dir, struct dentry *new_dentry)
+{
+	struct super_block *sb = old_dir->i_sb;
+	struct buffer_head *bh = NULL;
+	int retval;
+
+	retval = affs_check_name(new_dentry->d_name.name,
+				 new_dentry->d_name.len,
+				 affs_nofilenametruncate(old_dentry));
+
+	if (retval)
+		return retval;
+
+	/* Unlink destination if it already exists */
+	if (d_really_is_positive(new_dentry)) {
+		retval = affs_remove_header(new_dentry);
+		if (retval)
+			return retval;
+	}
+
+	bh = affs_bread(sb, d_inode(old_dentry)->i_ino);
+	if (!bh)
+		return -EIO;
+
+	/* Remove header from its parent directory. */
+	affs_lock_dir(old_dir);
+	retval = affs_remove_hash(old_dir, bh);
+	affs_unlock_dir(old_dir);
+	if (retval)
+		goto done;
+
+	/* And insert it into the new directory with the new name. */
+	affs_copy_name(AFFS_TAIL(sb, bh)->name, new_dentry);
+	affs_fix_checksum(sb, bh);
+	affs_lock_dir(new_dir);
+	retval = affs_insert_hash(new_dir, bh);
+	affs_unlock_dir(new_dir);
+	/* TODO: move it back to old_dir, if error? */
+
+done:
+	mark_buffer_dirty(bh);
+	affs_brelse(bh);
+	return retval;
+}
+
+static int
+affs_xrename(struct inode *old_dir, struct dentry *old_dentry,
+	     struct inode *new_dir, struct dentry *new_dentry)
+{
+
+	struct super_block *sb = old_dir->i_sb;
+	struct buffer_head *bh_old = NULL;
+	struct buffer_head *bh_new = NULL;
+	int retval;
+
+	bh_old = affs_bread(sb, d_inode(old_dentry)->i_ino);
+	if (!bh_old)
+		return -EIO;
+
+	bh_new = affs_bread(sb, d_inode(new_dentry)->i_ino);
+	if (!bh_new) {
+		affs_brelse(bh_old);
+		return -EIO;
+	}
+
+	/* Remove old header from its parent directory. */
+	affs_lock_dir(old_dir);
+	retval = affs_remove_hash(old_dir, bh_old);
+	affs_unlock_dir(old_dir);
+	if (retval)
+		goto done;
+
+	/* Remove new header from its parent directory. */
+	affs_lock_dir(new_dir);
+	retval = affs_remove_hash(new_dir, bh_new);
+	affs_unlock_dir(new_dir);
+	if (retval)
+		goto done;
+
+	/* Insert old into the new directory with the new name. */
+	affs_copy_name(AFFS_TAIL(sb, bh_old)->name, new_dentry);
+	affs_fix_checksum(sb, bh_old);
+	affs_lock_dir(new_dir);
+	retval = affs_insert_hash(new_dir, bh_old);
+	affs_unlock_dir(new_dir);
+
+	/* Insert new into the old directory with the old name. */
+	affs_copy_name(AFFS_TAIL(sb, bh_new)->name, old_dentry);
+	affs_fix_checksum(sb, bh_new);
+	affs_lock_dir(old_dir);
+	retval = affs_insert_hash(old_dir, bh_new);
+	affs_unlock_dir(old_dir);
+done:
+	mark_buffer_dirty(bh_old);
+	mark_buffer_dirty(bh_new);
+	affs_brelse(bh_old);
+	affs_brelse(bh_new);
+	return retval;
+}
+
+int affs_rename2(struct mnt_idmap *idmap, struct inode *old_dir,
+		 struct dentry *old_dentry, struct inode *new_dir,
+		 struct dentry *new_dentry, unsigned int flags)
+{
+
+	if (flags & ~(RENAME_NOREPLACE | RENAME_EXCHANGE))
+		return -EINVAL;
+
+	pr_debug("%s(old=%llu,\"%pd\" to new=%llu,\"%pd\")\n", __func__,
+		 old_dir->i_ino, old_dentry, new_dir->i_ino, new_dentry);
+
+	if (flags & RENAME_EXCHANGE)
+		return affs_xrename(old_dir, old_dentry, new_dir, new_dentry);
+
+	return affs_rename(old_dir, old_dentry, new_dir, new_dentry);
+}
+
+static struct dentry *affs_get_parent(struct dentry *child)
+{
+	struct inode *parent;
+	struct buffer_head *bh;
+
+	bh = affs_bread(child->d_sb, d_inode(child)->i_ino);
+	if (!bh)
+		return ERR_PTR(-EIO);
+
+	parent = affs_iget(child->d_sb,
+			   be32_to_cpu(AFFS_TAIL(child->d_sb, bh)->parent));
+	brelse(bh);
+	return d_obtain_alias(parent);
+}
+
+static struct inode *affs_nfs_get_inode(struct super_block *sb, u64 ino,
+					u32 generation)
+{
+	struct inode *inode;
+
+	if (!affs_validblock(sb, ino))
+		return ERR_PTR(-ESTALE);
+
+	inode = affs_iget(sb, ino);
+	if (IS_ERR(inode))
+		return ERR_CAST(inode);
+
+	return inode;
+}
+
+static struct dentry *affs_fh_to_dentry(struct super_block *sb, struct fid *fid,
+					int fh_len, int fh_type)
+{
+	return generic_fh_to_dentry(sb, fid, fh_len, fh_type,
+				    affs_nfs_get_inode);
+}
+
+static struct dentry *affs_fh_to_parent(struct super_block *sb, struct fid *fid,
+					int fh_len, int fh_type)
+{
+	return generic_fh_to_parent(sb, fid, fh_len, fh_type,
+				    affs_nfs_get_inode);
+}
+
+const struct export_operations affs_export_ops = {
+	.encode_fh = generic_encode_ino32_fh,
+	.fh_to_dentry = affs_fh_to_dentry,
+	.fh_to_parent = affs_fh_to_parent,
+	.get_parent = affs_get_parent,
+};
+
+const struct dentry_operations affs_dentry_operations = {
+	.d_hash		= affs_hash_dentry,
+	.d_compare	= affs_compare_dentry,
+};
+
+const struct dentry_operations affs_intl_dentry_operations = {
+	.d_hash		= affs_intl_hash_dentry,
+	.d_compare	= affs_intl_compare_dentry,
+};