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, 88 insertions, 0 deletions

diff --git a/Documentation/admin-guide/device-mapper/dm-flakey.rst b/Documentation/admin-guide/device-mapper/dm-flakey.rst
new file mode 100644
index 000000000..f967c5fea
--- /dev/null
+++ b/Documentation/admin-guide/device-mapper/dm-flakey.rst
@@ -0,0 +1,88 @@
+=========
+dm-flakey
+=========
+
+This target is the same as the linear target except that it exhibits
+unreliable behaviour periodically.  It's been found useful in simulating
+failing devices for testing purposes.
+
+Starting from the time the table is loaded, the device is available for
+<up interval> seconds, then exhibits unreliable behaviour for <down
+interval> seconds, and then this cycle repeats.
+
+Also, consider using this in combination with the dm-delay target too,
+which can delay reads and writes and/or send them to different
+underlying devices.
+
+Table parameters
+----------------
+
+::
+
+  <dev path> <offset> <up interval> <down interval> \
+    [<num_features> [<feature arguments>]]
+
+Mandatory parameters:
+
+    <dev path>:
+        Full pathname to the underlying block-device, or a
+        "major:minor" device-number.
+    <offset>:
+        Starting sector within the device.
+    <up interval>:
+        Number of seconds device is available.
+    <down interval>:
+        Number of seconds device returns errors.
+
+Optional feature parameters:
+
+  If no feature parameters are present, during the periods of
+  unreliability, all I/O returns errors.
+
+  error_reads:
+	All read I/O is failed with an error signalled.
+	Write I/O is handled correctly.
+
+  drop_writes:
+	All write I/O is silently ignored.
+	Read I/O is handled correctly.
+
+  error_writes:
+	All write I/O is failed with an error signalled.
+	Read I/O is handled correctly.
+
+  corrupt_bio_byte <Nth_byte> <direction> <value> <flags>:
+	During <down interval>, replace <Nth_byte> of the data of
+	each matching bio with <value>.
+
+    <Nth_byte>:
+	The offset of the byte to replace.
+	Counting starts at 1, to replace the first byte.
+    <direction>:
+	Either 'r' to corrupt reads or 'w' to corrupt writes.
+	'w' is incompatible with drop_writes.
+    <value>:
+	The value (from 0-255) to write.
+    <flags>:
+	Perform the replacement only if bio->bi_opf has all the
+	selected flags set.
+
+  random_read_corrupt <probability>
+	During <down interval>, replace random byte in a read bio
+	with a random value. probability is an integer between
+	0 and 1000000000 meaning 0% to 100% probability of corruption.
+
+  random_write_corrupt <probability>
+	During <down interval>, replace random byte in a write bio
+	with a random value. probability is an integer between
+	0 and 1000000000 meaning 0% to 100% probability of corruption.
+
+Examples:
+
+Replaces the 32nd byte of READ bios with the value 1::
+
+  corrupt_bio_byte 32 r 1 0
+
+Replaces the 224th byte of REQ_META (=32) bios with the value 0::
+
+  corrupt_bio_byte 224 w 0 32