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, 75 insertions, 0 deletions

diff --git a/Documentation/filesystems/udf.rst b/Documentation/filesystems/udf.rst
new file mode 100644
index 000000000..f9489ddbb
--- /dev/null
+++ b/Documentation/filesystems/udf.rst
@@ -0,0 +1,75 @@
+.. SPDX-License-Identifier: GPL-2.0
+
+===============
+UDF file system
+===============
+
+If you encounter problems with reading UDF discs using this driver,
+please report them according to MAINTAINERS file.
+
+Write support requires a block driver which supports writing.  Currently
+dvd+rw drives and media support true random sector writes, and so a udf
+filesystem on such devices can be directly mounted read/write.  CD-RW
+media however, does not support this.  Instead the media can be formatted
+for packet mode using the utility cdrwtool, then the pktcdvd driver can
+be bound to the underlying cd device to provide the required buffering
+and read-modify-write cycles to allow the filesystem random sector writes
+while providing the hardware with only full packet writes.  While not
+required for dvd+rw media, use of the pktcdvd driver often enhances
+performance due to very poor read-modify-write support supplied internally
+by drive firmware.
+
+-------------------------------------------------------------------------------
+
+The following mount options are supported:
+
+	===========	======================================
+	gid=		Set the default group.
+	umask=		Set the default umask.
+	mode=		Set the default file permissions.
+	dmode=		Set the default directory permissions.
+	uid=		Set the default user.
+	bs=		Set the block size.
+	unhide		Show otherwise hidden files.
+	undelete	Show deleted files in lists.
+	adinicb		Embed data in the inode (default)
+	noadinicb	Don't embed data in the inode
+	shortad		Use short ad's
+	longad		Use long ad's (default)
+	nostrict	Unset strict conformance
+	iocharset=	Set the NLS character set
+	===========	======================================
+
+The uid= and gid= options need a bit more explaining.  They will accept a
+decimal numeric value and all inodes on that mount will then appear as
+belonging to that uid and gid.  Mount options also accept the string "forget".
+The forget option causes all IDs to be written to disk as -1 which is a way
+of UDF standard to indicate that IDs are not supported for these files .
+
+For typical desktop use of removable media, you should set the ID to that of
+the interactively logged on user, and also specify the forget option.  This way
+the interactive user will always see the files on the disk as belonging to him.
+
+The remaining are for debugging and disaster recovery:
+
+	=====		================================
+	novrs		Skip volume sequence recognition
+	=====		================================
+
+The following expect a offset from 0.
+
+	==========	=================================================
+	session=	Set the CDROM session (default= last session)
+	anchor=		Override standard anchor location. (default= 256)
+	lastblock=	Set the last block of the filesystem/
+	==========	=================================================
+
+-------------------------------------------------------------------------------
+
+
+For the latest version and toolset see:
+	https://github.com/pali/udftools
+
+Documentation on UDF and ECMA 167 is available FREE from:
+	- http://www.osta.org/
+	- https://www.ecma-international.org/