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/sysfs.h b/fs/btrfs/sysfs.h
new file mode 100644
index 000000000..05498e534
--- /dev/null
+++ b/fs/btrfs/sysfs.h
@@ -0,0 +1,57 @@
+/* SPDX-License-Identifier: GPL-2.0 */
+
+#ifndef BTRFS_SYSFS_H
+#define BTRFS_SYSFS_H
+
+#include <linux/types.h>
+#include <linux/compiler_types.h>
+#include <linux/kobject.h>
+
+struct block_device;
+struct btrfs_fs_info;
+struct btrfs_device;
+struct btrfs_fs_devices;
+struct btrfs_block_group;
+struct btrfs_space_info;
+struct btrfs_qgroup;
+
+enum btrfs_feature_set {
+	FEAT_COMPAT,
+	FEAT_COMPAT_RO,
+	FEAT_INCOMPAT,
+	FEAT_MAX
+};
+
+char *btrfs_printable_features(enum btrfs_feature_set set, u64 flags);
+const char *btrfs_feature_set_name(enum btrfs_feature_set set);
+int btrfs_sysfs_add_device(struct btrfs_device *device);
+void btrfs_sysfs_remove_device(struct btrfs_device *device);
+int btrfs_sysfs_add_fsid(struct btrfs_fs_devices *fs_devs);
+void btrfs_sysfs_remove_fsid(struct btrfs_fs_devices *fs_devs);
+void btrfs_sysfs_update_sprout_fsid(struct btrfs_fs_devices *fs_devices);
+void btrfs_sysfs_feature_update(struct btrfs_fs_info *fs_info);
+void btrfs_kobject_uevent(struct block_device *bdev, enum kobject_action action);
+
+int __init btrfs_init_sysfs(void);
+void __cold btrfs_exit_sysfs(void);
+int btrfs_sysfs_add_mounted(struct btrfs_fs_info *fs_info);
+void btrfs_sysfs_remove_mounted(struct btrfs_fs_info *fs_info);
+void btrfs_sysfs_add_block_group_type(struct btrfs_block_group *cache);
+int btrfs_sysfs_add_space_info_type(struct btrfs_space_info *space_info);
+void btrfs_sysfs_remove_space_info(struct btrfs_space_info *space_info);
+void btrfs_sysfs_update_devid(struct btrfs_device *device);
+
+int btrfs_sysfs_add_one_qgroup(struct btrfs_fs_info *fs_info,
+				struct btrfs_qgroup *qgroup);
+void btrfs_sysfs_del_qgroups(struct btrfs_fs_info *fs_info);
+int btrfs_sysfs_add_qgroups(struct btrfs_fs_info *fs_info);
+void btrfs_sysfs_del_one_qgroup(struct btrfs_fs_info *fs_info,
+				struct btrfs_qgroup *qgroup);
+int btrfs_read_policy_to_enum(const char *str, s64 *value);
+
+#ifdef CONFIG_BTRFS_EXPERIMENTAL
+int __init btrfs_read_policy_init(void);
+char *btrfs_get_mod_read_policy(void);
+#endif
+
+#endif