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, 48 insertions, 0 deletions

diff --git a/drivers/rtc/rtc-s3c.h b/drivers/rtc/rtc-s3c.h
new file mode 100644
index 000000000..11d7a1255
--- /dev/null
+++ b/drivers/rtc/rtc-s3c.h
@@ -0,0 +1,48 @@
+/* SPDX-License-Identifier: GPL-2.0-only */
+/*
+ * Copyright (c) 2003 Simtec Electronics <linux@simtec.co.uk>
+ *		      http://www.simtec.co.uk/products/SWLINUX/
+ *
+ * S3C2410 Internal RTC register definition
+*/
+
+#ifndef __ASM_ARCH_REGS_RTC_H
+#define __ASM_ARCH_REGS_RTC_H __FILE__
+
+#define S3C2410_RTCREG(x) (x)
+#define S3C2410_INTP		S3C2410_RTCREG(0x30)
+#define S3C2410_INTP_ALM	(1 << 1)
+#define S3C2410_INTP_TIC	(1 << 0)
+
+#define S3C2410_RTCCON		S3C2410_RTCREG(0x40)
+#define S3C2410_RTCCON_RTCEN	(1 << 0)
+#define S3C2410_RTCCON_CNTSEL	(1 << 2)
+#define S3C2410_RTCCON_CLKRST	(1 << 3)
+#define S3C2443_RTCCON_TICSEL	(1 << 4)
+#define S3C64XX_RTCCON_TICEN	(1 << 8)
+
+#define S3C2410_RTCALM		S3C2410_RTCREG(0x50)
+#define S3C2410_RTCALM_ALMEN	(1 << 6)
+#define S3C2410_RTCALM_YEAREN	(1 << 5)
+#define S3C2410_RTCALM_MONEN	(1 << 4)
+#define S3C2410_RTCALM_DAYEN	(1 << 3)
+#define S3C2410_RTCALM_HOUREN	(1 << 2)
+#define S3C2410_RTCALM_MINEN	(1 << 1)
+#define S3C2410_RTCALM_SECEN	(1 << 0)
+
+#define S3C2410_ALMSEC		S3C2410_RTCREG(0x54)
+#define S3C2410_ALMMIN		S3C2410_RTCREG(0x58)
+#define S3C2410_ALMHOUR		S3C2410_RTCREG(0x5c)
+
+#define S3C2410_ALMDATE		S3C2410_RTCREG(0x60)
+#define S3C2410_ALMMON		S3C2410_RTCREG(0x64)
+#define S3C2410_ALMYEAR		S3C2410_RTCREG(0x68)
+
+#define S3C2410_RTCSEC		S3C2410_RTCREG(0x70)
+#define S3C2410_RTCMIN		S3C2410_RTCREG(0x74)
+#define S3C2410_RTCHOUR		S3C2410_RTCREG(0x78)
+#define S3C2410_RTCDATE		S3C2410_RTCREG(0x7c)
+#define S3C2410_RTCMON		S3C2410_RTCREG(0x84)
+#define S3C2410_RTCYEAR		S3C2410_RTCREG(0x88)
+
+#endif /* __ASM_ARCH_REGS_RTC_H */