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, 194 insertions, 0 deletions

diff --git a/Documentation/userspace-api/netlink/netlink-raw.rst b/Documentation/userspace-api/netlink/netlink-raw.rst
new file mode 100644
index 000000000..aae296c17
--- /dev/null
+++ b/Documentation/userspace-api/netlink/netlink-raw.rst
@@ -0,0 +1,194 @@
+.. SPDX-License-Identifier: BSD-3-Clause
+
+======================================================
+Netlink specification support for raw Netlink families
+======================================================
+
+This document describes the additional properties required by raw Netlink
+families such as ``NETLINK_ROUTE`` which use the ``netlink-raw`` protocol
+specification.
+
+Specification
+=============
+
+The netlink-raw schema extends the :doc:`genetlink-legacy <genetlink-legacy>`
+schema with properties that are needed to specify the protocol numbers and
+multicast IDs used by raw netlink families. See :ref:`classic_netlink` for more
+information. The raw netlink families also make use of type-specific
+sub-messages.
+
+Globals
+-------
+
+protonum
+~~~~~~~~
+
+The ``protonum`` property is used to specify the protocol number to use when
+opening a netlink socket.
+
+.. code-block:: yaml
+
+  # SPDX-License-Identifier: ((GPL-2.0 WITH Linux-syscall-note) OR BSD-3-Clause)
+
+  name: rt-addr
+  protocol: netlink-raw
+  protonum: 0             # part of the NETLINK_ROUTE protocol
+
+
+Multicast group properties
+--------------------------
+
+value
+~~~~~
+
+The ``value`` property is used to specify the group ID to use for multicast
+group registration.
+
+.. code-block:: yaml
+
+  mcast-groups:
+    list:
+      -
+        name: rtnlgrp-ipv4-ifaddr
+        value: 5
+      -
+        name: rtnlgrp-ipv6-ifaddr
+        value: 9
+      -
+        name: rtnlgrp-mctp-ifaddr
+        value: 34
+
+Sub-messages
+------------
+
+Several raw netlink families such as
+:ref:`rt-link<netlink-rt-link>` and
+:ref:`tc<netlink-tc>` use attribute nesting as an
+abstraction to carry module specific information.
+
+Conceptually it looks as follows::
+
+    [OUTER NEST OR MESSAGE LEVEL]
+      [GENERIC ATTR 1]
+      [GENERIC ATTR 2]
+      [GENERIC ATTR 3]
+      [GENERIC ATTR - wrapper]
+        [MODULE SPECIFIC ATTR 1]
+        [MODULE SPECIFIC ATTR 2]
+
+The ``GENERIC ATTRs`` at the outer level are defined in the core (or rt_link or
+core TC), while specific drivers, TC classifiers, qdiscs etc. can carry their
+own information wrapped in the ``GENERIC ATTR - wrapper``. Even though the
+example above shows attributes nesting inside the wrapper, the modules generally
+have full freedom to define the format of the nest. In practice the payload of
+the wrapper attr has very similar characteristics to a netlink message. It may
+contain a fixed header / structure, netlink attributes, or both. Because of
+those shared characteristics we refer to the payload of the wrapper attribute as
+a sub-message.
+
+A sub-message attribute uses the value of another attribute as a selector key to
+choose the right sub-message format. For example if the following attribute has
+already been decoded:
+
+.. code-block:: json
+
+  { "kind": "gre" }
+
+and we encounter the following attribute spec:
+
+.. code-block:: yaml
+
+  -
+    name: data
+    type: sub-message
+    sub-message: linkinfo-data-msg
+    selector: kind
+
+Then we look for a sub-message definition called ``linkinfo-data-msg`` and use
+the value of the ``kind`` attribute i.e. ``gre`` as the key to choose the
+correct format for the sub-message:
+
+.. code-block:: yaml
+
+  sub-messages:
+    name: linkinfo-data-msg
+    formats:
+      -
+        value: bridge
+        attribute-set: linkinfo-bridge-attrs
+      -
+        value: gre
+        attribute-set: linkinfo-gre-attrs
+      -
+        value: geneve
+        attribute-set: linkinfo-geneve-attrs
+
+This would decode the attribute value as a sub-message with the attribute-set
+called ``linkinfo-gre-attrs`` as the attribute space.
+
+A sub-message can have an optional ``fixed-header`` followed by zero or more
+attributes from an ``attribute-set``. For example the following
+``tc-options-msg`` sub-message defines message formats that use a mixture of
+``fixed-header``, ``attribute-set`` or both together:
+
+.. code-block:: yaml
+
+  sub-messages:
+    -
+      name: tc-options-msg
+      formats:
+        -
+          value: bfifo
+          fixed-header: tc-fifo-qopt
+        -
+          value: cake
+          attribute-set: tc-cake-attrs
+        -
+          value: netem
+          fixed-header: tc-netem-qopt
+          attribute-set: tc-netem-attrs
+
+Note that a selector attribute must appear in a netlink message before any
+sub-message attributes that depend on it.
+
+If an attribute such as ``kind`` is defined at more than one nest level, then a
+sub-message selector will be resolved using the value 'closest' to the selector.
+For example, if the same attribute name is defined in a nested ``attribute-set``
+alongside a sub-message selector and also in a top level ``attribute-set``, then
+the selector will be resolved using the value 'closest' to the selector. If the
+value is not present in the message at the same level as defined in the spec
+then this is an error.
+
+Nested struct definitions
+-------------------------
+
+Many raw netlink families such as :ref:`tc<netlink-tc>`
+make use of nested struct definitions. The ``netlink-raw`` schema makes it
+possible to embed a struct within a struct definition using the ``struct``
+property. For example, the following struct definition embeds the
+``tc-ratespec`` struct definition for both the ``rate`` and the ``peakrate``
+members of ``struct tc-tbf-qopt``.
+
+.. code-block:: yaml
+
+  -
+    name: tc-tbf-qopt
+    type: struct
+    members:
+      -
+        name: rate
+        type: binary
+        struct: tc-ratespec
+      -
+        name: peakrate
+        type: binary
+        struct: tc-ratespec
+      -
+        name: limit
+        type: u32
+      -
+        name: buffer
+        type: u32
+      -
+        name: mtu
+        type: u32