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, 80 insertions, 0 deletions

diff --git a/arch/arc/lib/strlen.S b/arch/arc/lib/strlen.S
new file mode 100644
index 000000000..dae428ceb
--- /dev/null
+++ b/arch/arc/lib/strlen.S
@@ -0,0 +1,80 @@
+/* SPDX-License-Identifier: GPL-2.0-only */
+/*
+ * Copyright (C) 2004, 2007-2010, 2011-2012 Synopsys, Inc. (www.synopsys.com)
+ */
+
+#include <linux/linkage.h>
+
+ENTRY_CFI(strlen)
+	or	r3,r0,7
+	ld	r2,[r3,-7]
+	ld.a	r6,[r3,-3]
+	mov	r4,0x01010101
+	; uses long immediate
+#ifdef __LITTLE_ENDIAN__
+	asl_s	r1,r0,3
+	btst_s	r0,2
+	asl	r7,r4,r1
+	ror	r5,r4
+	sub	r1,r2,r7
+	bic_s	r1,r1,r2
+	mov.eq	r7,r4
+	sub	r12,r6,r7
+	bic	r12,r12,r6
+	or.eq	r12,r12,r1
+	and	r12,r12,r5
+	brne	r12,0,.Learly_end
+#else /* BIG ENDIAN */
+	ror	r5,r4
+	btst_s	r0,2
+	mov_s	r1,31
+	sub3	r7,r1,r0
+	sub	r1,r2,r4
+	bic_s	r1,r1,r2
+	bmsk	r1,r1,r7
+	sub	r12,r6,r4
+	bic	r12,r12,r6
+	bmsk.ne	r12,r12,r7
+	or.eq	r12,r12,r1
+	and	r12,r12,r5
+	brne	r12,0,.Learly_end
+#endif /* ENDIAN */
+
+.Loop:
+	ld_s	r2,[r3,4]
+	ld.a	r6,[r3,8]
+	; stall for load result
+	sub	r1,r2,r4
+	bic_s	r1,r1,r2
+	sub	r12,r6,r4
+	bic	r12,r12,r6
+	or	r12,r12,r1
+	and	r12,r12,r5
+	breq r12,0,.Loop
+.Lend:
+	and.f	r1,r1,r5
+	sub.ne	r3,r3,4
+	mov.eq	r1,r12
+#ifdef __LITTLE_ENDIAN__
+	sub_s	r2,r1,1
+	bic_s	r2,r2,r1
+	norm	r1,r2
+	sub_s	r0,r0,3
+	lsr_s	r1,r1,3
+	sub	    r0,r3,r0
+	j_s.d	[blink]
+	sub	    r0,r0,r1
+#else /* BIG ENDIAN */
+	lsr_s	r1,r1,7
+	mov.eq	r2,r6
+	bic_s	r1,r1,r2
+	norm	r1,r1
+	sub	    r0,r3,r0
+	lsr_s	r1,r1,3
+	j_s.d	[blink]
+	add	    r0,r0,r1
+#endif /* ENDIAN */
+.Learly_end:
+	b.d	.Lend
+	sub_s.ne r1,r1,r1
+END_CFI(strlen)