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, 36 insertions, 0 deletions

diff --git a/arch/mips/alchemy/Kconfig b/arch/mips/alchemy/Kconfig
new file mode 100644
index 000000000..cf5ad52c0
--- /dev/null
+++ b/arch/mips/alchemy/Kconfig
@@ -0,0 +1,36 @@
+# SPDX-License-Identifier: GPL-2.0
+choice
+	prompt "Machine type"
+	depends on MIPS_ALCHEMY
+	default MIPS_DB1XXX
+
+config MIPS_MTX1
+	bool "4G Systems MTX-1 board"
+	select HAVE_PCI
+	select SYS_SUPPORTS_LITTLE_ENDIAN
+	select SYS_HAS_EARLY_PRINTK
+
+config MIPS_DB1XXX
+	bool "Alchemy DB1XXX / PB1XXX boards"
+	select HAVE_PCI
+	select HAVE_PATA_PLATFORM
+	select SYS_SUPPORTS_LITTLE_ENDIAN
+	select SYS_HAS_EARLY_PRINTK
+	help
+	  Select this option if you have one of the following Alchemy
+	  development boards:  DB1000 DB1500 DB1100 DB1550 DB1200 DB1300
+			       PB1500 PB1100 PB1550 PB1200
+	  Board type is autodetected during boot.
+
+config MIPS_XXS1500
+	bool "MyCable XXS1500 board"
+	select SYS_SUPPORTS_LITTLE_ENDIAN
+	select SYS_HAS_EARLY_PRINTK
+
+config MIPS_GPR
+	bool "Trapeze ITS GPR board"
+	select HAVE_PCI
+	select SYS_SUPPORTS_LITTLE_ENDIAN
+	select SYS_HAS_EARLY_PRINTK
+
+endchoice