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, 133 insertions, 0 deletions

diff --git a/Documentation/ABI/testing/sysfs-class-rnbd-client b/Documentation/ABI/testing/sysfs-class-rnbd-client
new file mode 100644
index 000000000..0b5997ab3
--- /dev/null
+++ b/Documentation/ABI/testing/sysfs-class-rnbd-client
@@ -0,0 +1,133 @@
+What:		/sys/class/rnbd-client
+Date:		Feb 2020
+KernelVersion:	5.7
+Contact:	Jack Wang <jinpu.wang@cloud.ionos.com> Danil Kipnis <danil.kipnis@cloud.ionos.com>
+Description:	Provide information about RNBD-client.
+		All sysfs files that are not read-only provide the usage information on read:
+
+		Example::
+
+		    # cat /sys/class/rnbd-client/ctl/map_device
+
+		    > Usage: echo "sessname=<name of the rtrs session> path=<[srcaddr,]dstaddr>
+		    > [path=<[srcaddr,]dstaddr>] device_path=<full path on remote side>
+		    > [access_mode=<ro|rw|migration>] > map_device
+		    >
+		    > addr ::= [ ip:<ipv4> | ip:<ipv6> | gid:<gid> ]
+
+What:		/sys/class/rnbd-client/ctl/map_device
+Date:		Feb 2020
+KernelVersion:	5.7
+Contact:	Jack Wang <jinpu.wang@cloud.ionos.com> Danil Kipnis <danil.kipnis@cloud.ionos.com>
+Description:	Expected format is the following::
+
+		    sessname=<name of the rtrs session>
+		    path=<[srcaddr,]dstaddr> [path=<[srcaddr,]dstaddr> ...]
+		    device_path=<full path on remote side>
+		    [access_mode=<ro|rw|migration>]
+
+		Where:
+
+		sessname:
+		    accepts a string not bigger than 256 chars, which identifies
+		    a given session on the client and on the server.
+		    I.e. "clt_hostname-srv_hostname" could be a natural choice.
+
+		path:
+		    describes a connection between the client and the server by
+		    specifying destination and, when required, the source address.
+		    The addresses are to be provided in the following format::
+
+			ip:<IPv6>
+			ip:<IPv4>
+			gid:<GID>
+
+		for example::
+
+		    path=ip:10.0.0.66
+
+		The single addr is treated as the destination.
+		The connection will be established to this server from any client IP address.
+
+		::
+
+		    path=ip:10.0.0.66,ip:10.0.1.66
+
+		First addr is the source address and the second is the destination.
+
+		If multiple "path=" options are specified multiple connection
+		will be established and data will be sent according to
+		the selected multipath policy (see RTRS mp_policy sysfs entry description).
+
+		device_path:
+		    Path to the block device on the server side. Path is specified
+		    relative to the directory on server side configured in the
+		    'dev_search_path' module parameter of the rnbd_server.
+		    The rnbd_server prepends the <device_path> received from client
+		    with <dev_search_path> and tries to open the
+		    <dev_search_path>/<device_path> block device.  On success,
+		    a /dev/rnbd<N> device file, a /sys/block/rnbd<N>/
+		    directory and an entry in /sys/class/rnbd-client/ctl/devices
+		    will be created.
+
+		If 'dev_search_path' contains '%SESSNAME%', then each session can
+		have different devices namespace, e.g. server was configured with
+		the following parameter "dev_search_path=/run/rnbd-devs/%SESSNAME%",
+		client has this string "sessname=blya device_path=sda", then server
+		will try to open: /run/rnbd-devs/blya/sda.
+
+		access_mode:
+		    the access_mode parameter specifies if the device is to be
+		    mapped as "ro" read-only or "rw" read-write. The server allows
+		    a device to be exported in rw mode only once. The "migration"
+		    access mode has to be specified if a second mapping in read-write
+		    mode is desired.
+
+		By default "rw" is used.
+
+		nr_poll_queues
+		  specifies the number of poll-mode queues. If the IO has HIPRI flag,
+		  the block-layer will send the IO via the poll-mode queue.
+		  For fast network and device the polling is faster than interrupt-base
+		  IO handling because it saves time for context switching, switching to
+		  another process, handling the interrupt and switching back to the
+		  issuing process.
+
+		  Set -1 if you want to set it as the number of CPUs
+		  By default rnbd client creates only irq-mode queues.
+
+		  NOTICE: MUST make a unique session for a device using the poll-mode queues.
+
+		Exit Codes:
+
+		If the device is already mapped it will fail with EEXIST. If the input
+		has an invalid format it will return EINVAL. If the device path cannot
+		be found on the server, it will fail with ENOENT.
+
+		Finding device file after mapping
+		---------------------------------
+
+		After mapping, the device file can be found by:
+		o  The symlink /sys/class/rnbd-client/ctl/devices/<device_id>@<session_name>
+		points to /sys/block/<dev-name>. The last part of the symlink destination
+		is the same as the device name.  By extracting the last part of the
+		path the path to the device /dev/<dev-name> can be build.
+
+		* /dev/block/$(cat /sys/class/rnbd-client/ctl/devices/<device_id>@<session_name>/dev)
+
+		How to find the <device_id> of the device is described on the next
+		section.
+
+What:		/sys/class/rnbd-client/ctl/devices/
+Date:		Feb 2020
+KernelVersion:	5.7
+Contact:	Jack Wang <jinpu.wang@cloud.ionos.com> Danil Kipnis <danil.kipnis@cloud.ionos.com>
+Description:	For each device mapped on the client a new symbolic link is created as
+		/sys/class/rnbd-client/ctl/devices/<device_id>@<session_name>, which points
+		to the block device created by rnbd (/sys/block/rnbd<N>/).
+		The <device_id> of each device is created as follows:
+
+		- If the 'device_path' provided during mapping contains slashes ("/"),
+		  they are replaced by exclamation mark ("!") and used as as the
+		  <device_id>. Otherwise, the <device_id> will be the same as the
+		  "device_path" provided.