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, 45 insertions, 0 deletions

diff --git a/fs/ufs/Kconfig b/fs/ufs/Kconfig
new file mode 100644
index 000000000..9301e7ecd
--- /dev/null
+++ b/fs/ufs/Kconfig
@@ -0,0 +1,45 @@
+# SPDX-License-Identifier: GPL-2.0-only
+config UFS_FS
+	tristate "UFS file system support (read only)"
+	depends on BLOCK
+	select BUFFER_HEAD
+	help
+	  BSD and derivate versions of Unix (such as SunOS, FreeBSD, NetBSD,
+	  OpenBSD and NeXTstep) use a file system called UFS. Some System V
+	  Unixes can create and mount hard disk partitions and diskettes using
+	  this file system as well. Saying Y here will allow you to read from
+	  these partitions; if you also want to write to them, say Y to the
+	  experimental "UFS file system write support", below. Please read the
+	  file <file:Documentation/admin-guide/ufs.rst> for more information.
+
+          The recently released UFS2 variant (used in FreeBSD 5.x) is
+          READ-ONLY supported.
+
+	  Note that this option is generally not needed for floppies, since a
+	  good portable way to transport files and directories between unixes
+	  (and even other operating systems) is given by the tar program ("man
+	  tar" or preferably "info tar").
+
+	  When accessing NeXTstep files, you may need to convert them from the
+	  NeXT character set to the Latin1 character set; use the program
+	  recode ("info recode") for this purpose.
+
+	  To compile the UFS file system support as a module, choose M here: the
+	  module will be called ufs.
+
+	  If you haven't heard about all of this before, it's safe to say N.
+
+config UFS_FS_WRITE
+	bool "UFS file system write support (DANGEROUS)"
+	depends on UFS_FS
+	help
+	  Say Y here if you want to try writing to UFS partitions. This is
+	  experimental, so you should back up your UFS partitions beforehand.
+
+config UFS_DEBUG
+	bool "UFS debugging"
+	depends on UFS_FS
+	help
+	  If you are experiencing any problems with the UFS filesystem, say
+	  Y here.  This will result in _many_ additional debugging messages to be
+	  written to the system log.