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, 320 insertions, 0 deletions

diff --git a/Documentation/networking/mctp.rst b/Documentation/networking/mctp.rst
new file mode 100644
index 000000000..c628cb540
--- /dev/null
+++ b/Documentation/networking/mctp.rst
@@ -0,0 +1,320 @@
+.. SPDX-License-Identifier: GPL-2.0
+
+==============================================
+Management Component Transport Protocol (MCTP)
+==============================================
+
+net/mctp/ contains protocol support for MCTP, as defined by DMTF standard
+DSP0236. Physical interface drivers ("bindings" in the specification) are
+provided in drivers/net/mctp/.
+
+The core code provides a socket-based interface to send and receive MCTP
+messages, through an AF_MCTP, SOCK_DGRAM socket.
+
+Structure: interfaces & networks
+================================
+
+The kernel models the local MCTP topology through two items: interfaces and
+networks.
+
+An interface (or "link") is an instance of an MCTP physical transport binding
+(as defined by DSP0236, section 3.2.47), likely connected to a specific hardware
+device. This is represented as a ``struct netdevice``.
+
+A network defines a unique address space for MCTP endpoints by endpoint-ID
+(described by DSP0236, section 3.2.31). A network has a user-visible identifier
+to allow references from userspace. Route definitions are specific to one
+network.
+
+Interfaces are associated with one network. A network may be associated with one
+or more interfaces.
+
+If multiple networks are present, each may contain endpoint IDs (EIDs) that are
+also present on other networks.
+
+Sockets API
+===========
+
+Protocol definitions
+--------------------
+
+MCTP uses ``AF_MCTP`` / ``PF_MCTP`` for the address- and protocol- families.
+Since MCTP is message-based, only ``SOCK_DGRAM`` sockets are supported.
+
+.. code-block:: C
+
+    int sd = socket(AF_MCTP, SOCK_DGRAM, 0);
+
+The only (current) value for the ``protocol`` argument is 0.
+
+As with all socket address families, source and destination addresses are
+specified with a ``sockaddr`` type, with a single-byte endpoint address:
+
+.. code-block:: C
+
+    typedef __u8		mctp_eid_t;
+
+    struct mctp_addr {
+            mctp_eid_t		s_addr;
+    };
+
+    struct sockaddr_mctp {
+            __kernel_sa_family_t smctp_family;
+            unsigned int         smctp_network;
+            struct mctp_addr     smctp_addr;
+            __u8                 smctp_type;
+            __u8                 smctp_tag;
+    };
+
+    #define MCTP_NET_ANY	0x0
+    #define MCTP_ADDR_ANY	0xff
+
+
+Syscall behaviour
+-----------------
+
+The following sections describe the MCTP-specific behaviours of the standard
+socket system calls. These behaviours have been chosen to map closely to the
+existing sockets APIs.
+
+``bind()`` : set local socket address
+^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^
+
+Sockets that receive incoming request packets will bind to a local address,
+using the ``bind()`` syscall.
+
+.. code-block:: C
+
+    struct sockaddr_mctp addr;
+
+    addr.smctp_family = AF_MCTP;
+    addr.smctp_network = MCTP_NET_ANY;
+    addr.smctp_addr.s_addr = MCTP_ADDR_ANY;
+    addr.smctp_type = MCTP_TYPE_PLDM;
+    addr.smctp_tag = MCTP_TAG_OWNER;
+
+    int rc = bind(sd, (struct sockaddr *)&addr, sizeof(addr));
+
+This establishes the local address of the socket. Incoming MCTP messages that
+match the network, address, and message type will be received by this socket.
+The reference to 'incoming' is important here; a bound socket will only receive
+messages with the TO bit set, to indicate an incoming request message, rather
+than a response.
+
+The ``smctp_tag`` value will configure the tags accepted from the remote side of
+this socket. Given the above, the only valid value is ``MCTP_TAG_OWNER``, which
+will result in remotely "owned" tags being routed to this socket. Since
+``MCTP_TAG_OWNER`` is set, the 3 least-significant bits of ``smctp_tag`` are not
+used; callers must set them to zero.
+
+A ``smctp_network`` value of ``MCTP_NET_ANY`` will configure the socket to
+receive incoming packets from any locally-connected network. A specific network
+value will cause the socket to only receive incoming messages from that network.
+
+The ``smctp_addr`` field specifies a local address to bind to. A value of
+``MCTP_ADDR_ANY`` configures the socket to receive messages addressed to any
+local destination EID.
+
+The ``smctp_type`` field specifies which message types to receive. Only the
+lower 7 bits of the type is matched on incoming messages (ie., the
+most-significant IC bit is not part of the match). This results in the socket
+receiving packets with and without a message integrity check footer.
+
+``sendto()``, ``sendmsg()``, ``send()`` : transmit an MCTP message
+^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^
+
+An MCTP message is transmitted using one of the ``sendto()``, ``sendmsg()`` or
+``send()`` syscalls. Using ``sendto()`` as the primary example:
+
+.. code-block:: C
+
+    struct sockaddr_mctp addr;
+    char buf[14];
+    ssize_t len;
+
+    /* set message destination */
+    addr.smctp_family = AF_MCTP;
+    addr.smctp_network = 0;
+    addr.smctp_addr.s_addr = 8;
+    addr.smctp_tag = MCTP_TAG_OWNER;
+    addr.smctp_type = MCTP_TYPE_ECHO;
+
+    /* arbitrary message to send, with message-type header */
+    buf[0] = MCTP_TYPE_ECHO;
+    memcpy(buf + 1, "hello, world!", sizeof(buf) - 1);
+
+    len = sendto(sd, buf, sizeof(buf), 0,
+                    (struct sockaddr_mctp *)&addr, sizeof(addr));
+
+The network and address fields of ``addr`` define the remote address to send to.
+If ``smctp_tag`` has the ``MCTP_TAG_OWNER``, the kernel will ignore any bits set
+in ``MCTP_TAG_VALUE``, and generate a tag value suitable for the destination
+EID. If ``MCTP_TAG_OWNER`` is not set, the message will be sent with the tag
+value as specified. If a tag value cannot be allocated, the system call will
+report an errno of ``EAGAIN``.
+
+The application must provide the message type byte as the first byte of the
+message buffer passed to ``sendto()``. If a message integrity check is to be
+included in the transmitted message, it must also be provided in the message
+buffer, and the most-significant bit of the message type byte must be 1.
+
+The ``sendmsg()`` system call allows a more compact argument interface, and the
+message buffer to be specified as a scatter-gather list. At present no ancillary
+message types (used for the ``msg_control`` data passed to ``sendmsg()``) are
+defined.
+
+Transmitting a message on an unconnected socket with ``MCTP_TAG_OWNER``
+specified will cause an allocation of a tag, if no valid tag is already
+allocated for that destination. The (destination-eid,tag) tuple acts as an
+implicit local socket address, to allow the socket to receive responses to this
+outgoing message. If any previous allocation has been performed (to for a
+different remote EID), that allocation is lost.
+
+Sockets will only receive responses to requests they have sent (with TO=1) and
+may only respond (with TO=0) to requests they have received.
+
+``recvfrom()``, ``recvmsg()``, ``recv()`` : receive an MCTP message
+^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^
+
+An MCTP message can be received by an application using one of the
+``recvfrom()``, ``recvmsg()``, or ``recv()`` system calls. Using ``recvfrom()``
+as the primary example:
+
+.. code-block:: C
+
+    struct sockaddr_mctp addr;
+    socklen_t addrlen;
+    char buf[14];
+    ssize_t len;
+
+    addrlen = sizeof(addr);
+
+    len = recvfrom(sd, buf, sizeof(buf), 0,
+                    (struct sockaddr_mctp *)&addr, &addrlen);
+
+    /* We can expect addr to describe an MCTP address */
+    assert(addrlen >= sizeof(buf));
+    assert(addr.smctp_family == AF_MCTP);
+
+    printf("received %zd bytes from remote EID %d\n", rc, addr.smctp_addr);
+
+The address argument to ``recvfrom`` and ``recvmsg`` is populated with the
+remote address of the incoming message, including tag value (this will be needed
+in order to reply to the message).
+
+The first byte of the message buffer will contain the message type byte. If an
+integrity check follows the message, it will be included in the received buffer.
+
+The ``recv()`` system call behaves in a similar way, but does not provide a
+remote address to the application. Therefore, these are only useful if the
+remote address is already known, or the message does not require a reply.
+
+Like the send calls, sockets will only receive responses to requests they have
+sent (TO=1) and may only respond (TO=0) to requests they have received.
+
+``ioctl(SIOCMCTPALLOCTAG)`` and ``ioctl(SIOCMCTPDROPTAG)``
+^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^
+
+These tags give applications more control over MCTP message tags, by allocating
+(and dropping) tag values explicitly, rather than the kernel automatically
+allocating a per-message tag at ``sendmsg()`` time.
+
+In general, you will only need to use these ioctls if your MCTP protocol does
+not fit the usual request/response model. For example, if you need to persist
+tags across multiple requests, or a request may generate more than one response.
+In these cases, the ioctls allow you to decouple the tag allocation (and
+release) from individual message send and receive operations.
+
+Both ioctls are passed a pointer to a ``struct mctp_ioc_tag_ctl``:
+
+.. code-block:: C
+
+    struct mctp_ioc_tag_ctl {
+        mctp_eid_t      peer_addr;
+        __u8		tag;
+        __u16   	flags;
+    };
+
+``SIOCMCTPALLOCTAG`` allocates a tag for a specific peer, which an application
+can use in future ``sendmsg()`` calls. The application populates the
+``peer_addr`` member with the remote EID. Other fields must be zero.
+
+On return, the ``tag`` member will be populated with the allocated tag value.
+The allocated tag will have the following tag bits set:
+
+ - ``MCTP_TAG_OWNER``: it only makes sense to allocate tags if you're the tag
+   owner
+
+ - ``MCTP_TAG_PREALLOC``: to indicate to ``sendmsg()`` that this is a
+   preallocated tag.
+
+ - ... and the actual tag value, within the least-significant three bits
+   (``MCTP_TAG_MASK``). Note that zero is a valid tag value.
+
+The tag value should be used as-is for the ``smctp_tag`` member of ``struct
+sockaddr_mctp``.
+
+``SIOCMCTPDROPTAG`` releases a tag that has been previously allocated by a
+``SIOCMCTPALLOCTAG`` ioctl. The ``peer_addr`` must be the same as used for the
+allocation, and the ``tag`` value must match exactly the tag returned from the
+allocation (including the ``MCTP_TAG_OWNER`` and ``MCTP_TAG_PREALLOC`` bits).
+The ``flags`` field must be zero.
+
+Kernel internals
+================
+
+There are a few possible packet flows in the MCTP stack:
+
+1. local TX to remote endpoint, message <= MTU::
+
+	sendmsg()
+	 -> mctp_local_output()
+	    : route lookup
+	    -> rt->output() (== mctp_route_output)
+	       -> dev_queue_xmit()
+
+2. local TX to remote endpoint, message > MTU::
+
+	sendmsg()
+	-> mctp_local_output()
+	    -> mctp_do_fragment_route()
+	       : creates packet-sized skbs. For each new skb:
+	       -> rt->output() (== mctp_route_output)
+	          -> dev_queue_xmit()
+
+3. remote TX to local endpoint, single-packet message::
+
+	mctp_pkttype_receive()
+	: route lookup
+	-> rt->output() (== mctp_route_input)
+	   : sk_key lookup
+	   -> sock_queue_rcv_skb()
+
+4. remote TX to local endpoint, multiple-packet message::
+
+	mctp_pkttype_receive()
+	: route lookup
+	-> rt->output() (== mctp_route_input)
+	   : sk_key lookup
+	   : stores skb in struct sk_key->reasm_head
+
+	mctp_pkttype_receive()
+	: route lookup
+	-> rt->output() (== mctp_route_input)
+	   : sk_key lookup
+	   : finds existing reassembly in sk_key->reasm_head
+	   : appends new fragment
+	   -> sock_queue_rcv_skb()
+
+Key refcounts
+-------------
+
+ * keys are refed by:
+
+   - a skb: during route output, stored in ``skb->cb``.
+
+   - netns and sock lists.
+
+ * keys can be associated with a device, in which case they hold a
+   reference to the dev (set through ``key->dev``, counted through
+   ``dev->key_count``). Multiple keys can reference the device.