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, 82 insertions, 0 deletions

diff --git a/Documentation/bpf/maps.rst b/Documentation/bpf/maps.rst
new file mode 100644
index 000000000..6f069f3d6
--- /dev/null
+++ b/Documentation/bpf/maps.rst
@@ -0,0 +1,82 @@
+
+========
+BPF maps
+========
+
+BPF 'maps' provide generic storage of different types for sharing data between
+kernel and user space. There are several storage types available, including
+hash, array, bloom filter and radix-tree. Several of the map types exist to
+support specific BPF helpers that perform actions based on the map contents. The
+maps are accessed from BPF programs via BPF helpers which are documented in the
+`man-pages`_ for `bpf-helpers(7)`_.
+
+BPF maps are accessed from user space via the ``bpf`` syscall, which provides
+commands to create maps, lookup elements, update elements and delete elements.
+More details of the BPF syscall are available in `ebpf-syscall`_ and in the
+`man-pages`_ for `bpf(2)`_.
+
+Map Types
+=========
+
+.. toctree::
+   :maxdepth: 1
+   :glob:
+
+   map_*
+
+Usage Notes
+===========
+
+.. c:function::
+   int bpf(int command, union bpf_attr *attr, u32 size)
+
+Use the ``bpf()`` system call to perform the operation specified by
+``command``. The operation takes parameters provided in ``attr``. The ``size``
+argument is the size of the ``union bpf_attr`` in ``attr``.
+
+**BPF_MAP_CREATE**
+
+Create a map with the desired type and attributes in ``attr``:
+
+.. code-block:: c
+
+    int fd;
+    union bpf_attr attr = {
+            .map_type = BPF_MAP_TYPE_ARRAY;  /* mandatory */
+            .key_size = sizeof(__u32);       /* mandatory */
+            .value_size = sizeof(__u32);     /* mandatory */
+            .max_entries = 256;              /* mandatory */
+            .map_flags = BPF_F_MMAPABLE;
+            .map_name = "example_array";
+    };
+
+    fd = bpf(BPF_MAP_CREATE, &attr, sizeof(attr));
+
+Returns a process-local file descriptor on success, or negative error in case of
+failure. The map can be deleted by calling ``close(fd)``. Maps held by open
+file descriptors will be deleted automatically when a process exits.
+
+.. note:: Valid characters for ``map_name`` are ``A-Z``, ``a-z``, ``0-9``,
+   ``'_'`` and ``'.'``.
+
+**BPF_MAP_LOOKUP_ELEM**
+
+Lookup key in a given map using ``attr->map_fd``, ``attr->key``,
+``attr->value``. Returns zero and stores found elem into ``attr->value`` on
+success, or negative error on failure.
+
+**BPF_MAP_UPDATE_ELEM**
+
+Create or update key/value pair in a given map using ``attr->map_fd``, ``attr->key``,
+``attr->value``. Returns zero on success or negative error on failure.
+
+**BPF_MAP_DELETE_ELEM**
+
+Find and delete element by key in a given map using ``attr->map_fd``,
+``attr->key``. Returns zero on success or negative error on failure.
+
+.. Links:
+.. _man-pages: https://www.kernel.org/doc/man-pages/
+.. _bpf(2): https://man7.org/linux/man-pages/man2/bpf.2.html
+.. _bpf-helpers(7): https://man7.org/linux/man-pages/man7/bpf-helpers.7.html
+.. _ebpf-syscall: https://docs.kernel.org/userspace-api/ebpf/syscall.html