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, 57 insertions, 0 deletions

diff --git a/fs/btrfs/dir-item.h b/fs/btrfs/dir-item.h
new file mode 100644
index 000000000..e52174a8b
--- /dev/null
+++ b/fs/btrfs/dir-item.h
@@ -0,0 +1,57 @@
+/* SPDX-License-Identifier: GPL-2.0 */
+
+#ifndef BTRFS_DIR_ITEM_H
+#define BTRFS_DIR_ITEM_H
+
+#include <linux/types.h>
+#include <linux/crc32c.h>
+
+struct fscrypt_str;
+struct btrfs_fs_info;
+struct btrfs_key;
+struct btrfs_path;
+struct btrfs_inode;
+struct btrfs_root;
+struct btrfs_trans_handle;
+
+int btrfs_check_dir_item_collision(struct btrfs_root *root, u64 dir_ino,
+			  const struct fscrypt_str *name);
+int btrfs_insert_dir_item(struct btrfs_trans_handle *trans,
+			  const struct fscrypt_str *name, struct btrfs_inode *dir,
+			  const struct btrfs_key *location, u8 type, u64 index);
+struct btrfs_dir_item *btrfs_lookup_dir_item(struct btrfs_trans_handle *trans,
+					     struct btrfs_root *root,
+					     struct btrfs_path *path, u64 dir,
+					     const struct fscrypt_str *name, int mod);
+struct btrfs_dir_item *btrfs_lookup_dir_index_item(
+			struct btrfs_trans_handle *trans,
+			struct btrfs_root *root,
+			struct btrfs_path *path, u64 dir,
+			u64 index, const struct fscrypt_str *name, int mod);
+struct btrfs_dir_item *btrfs_search_dir_index_item(struct btrfs_root *root,
+			    struct btrfs_path *path, u64 dirid,
+			    const struct fscrypt_str *name);
+int btrfs_delete_one_dir_name(struct btrfs_trans_handle *trans,
+			      struct btrfs_root *root,
+			      struct btrfs_path *path,
+			      const struct btrfs_dir_item *di);
+int btrfs_insert_xattr_item(struct btrfs_trans_handle *trans,
+			    struct btrfs_root *root,
+			    struct btrfs_path *path, u64 objectid,
+			    const char *name, u16 name_len,
+			    const void *data, u16 data_len);
+struct btrfs_dir_item *btrfs_lookup_xattr(struct btrfs_trans_handle *trans,
+					  struct btrfs_root *root,
+					  struct btrfs_path *path, u64 dir,
+					  const char *name, u16 name_len,
+					  int mod);
+struct btrfs_dir_item *btrfs_match_dir_item_name(const struct btrfs_path *path,
+						 const char *name,
+						 int name_len);
+
+static inline u64 btrfs_name_hash(const char *name, int len)
+{
+       return crc32c((u32)~1, name, len);
+}
+
+#endif