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, 91 insertions, 0 deletions

diff --git a/Documentation/ABI/testing/sysfs-class-rtc b/Documentation/ABI/testing/sysfs-class-rtc
new file mode 100644
index 000000000..95984289a
--- /dev/null
+++ b/Documentation/ABI/testing/sysfs-class-rtc
@@ -0,0 +1,91 @@
+What:		/sys/class/rtc/
+Date:		March 2006
+KernelVersion:	2.6.17
+Contact:	linux-rtc@vger.kernel.org
+Description:
+		The rtc/ class subdirectory belongs to the RTC subsystem.
+
+What:		/sys/class/rtc/rtcX/
+Date:		March 2006
+KernelVersion:	2.6.17
+Contact:	linux-rtc@vger.kernel.org
+Description:
+		The /sys/class/rtc/rtc{0,1,2,3,...} directories correspond
+		to each RTC device.
+
+What:		/sys/class/rtc/rtcX/date
+Date:		March 2006
+KernelVersion:	2.6.17
+Contact:	linux-rtc@vger.kernel.org
+Description:
+		(RO) RTC-provided date in YYYY-MM-DD format
+
+What:		/sys/class/rtc/rtcX/hctosys
+Date:		September 2009
+KernelVersion:	2.6.32
+Contact:	linux-rtc@vger.kernel.org
+Description:
+		(RO) 1 if the RTC provided the system time at boot via the
+		CONFIG_RTC_HCTOSYS kernel option, 0 otherwise
+
+What:		/sys/class/rtc/rtcX/max_user_freq
+Date:		October 2007
+KernelVersion:	2.6.24
+Contact:	linux-rtc@vger.kernel.org
+Description:
+		(RW) The maximum interrupt rate an unprivileged user may request
+		from this RTC.
+
+What:		/sys/class/rtc/rtcX/name
+Date:		March 2006
+KernelVersion:	2.6.17
+Contact:	linux-rtc@vger.kernel.org
+Description:
+		(RO) The name of the RTC corresponding to this sysfs directory
+
+What:		/sys/class/rtc/rtcX/range
+Date:		January 2018
+KernelVersion:	4.16
+Contact:	linux-rtc@vger.kernel.org
+Description:
+		Valid time range for the RTC, as seconds from epoch, formatted
+		as [min, max]
+
+What:		/sys/class/rtc/rtcX/since_epoch
+Date:		March 2006
+KernelVersion:	2.6.17
+Contact:	linux-rtc@vger.kernel.org
+Description:
+		(RO) RTC-provided time as the number of seconds since the epoch
+
+What:		/sys/class/rtc/rtcX/time
+Date:		March 2006
+KernelVersion:	2.6.17
+Contact:	linux-rtc@vger.kernel.org
+Description:
+		(RO) RTC-provided time in 24-hour notation (hh:mm:ss)
+
+What:		/sys/class/rtc/rtcX/offset
+Date:		February 2016
+KernelVersion:	4.6
+Contact:	linux-rtc@vger.kernel.org
+Description:
+		(RW) The amount which the rtc clock has been adjusted in
+		firmware. Visible only if the driver supports clock offset
+		adjustment. The unit is parts per billion, i.e. The number of
+		clock ticks which are added to or removed from the rtc's base
+		clock per billion ticks. A positive value makes a day pass more
+		slowly, longer, and a negative value makes a day pass more
+		quickly.
+
+What:		/sys/class/rtc/rtcX/wakealarm
+Date:		February 2007
+KernelVersion:	2.6.20
+Contact:	linux-rtc@vger.kernel.org
+Description:
+		(RW) The time at which the clock will generate a system wakeup
+		event. This is a one shot wakeup event, so must be reset after
+		wake if a daily wakeup is required. Format is seconds since the
+		epoch by default, or if there's a leading +, seconds in the
+		future, or if there is a leading +=, seconds ahead of the
+		current alarm.