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, 127 insertions, 0 deletions

diff --git a/arch/sparc/lib/mcount.S b/arch/sparc/lib/mcount.S
new file mode 100644
index 000000000..0309ba2c4
--- /dev/null
+++ b/arch/sparc/lib/mcount.S
@@ -0,0 +1,127 @@
+/* SPDX-License-Identifier: GPL-2.0 */
+/*
+ * Copyright (C) 2000 Anton Blanchard (anton@linuxcare.com)
+ *
+ * This file implements mcount(), which is used to collect profiling data.
+ * This can also be tweaked for kernel stack overflow detection.
+ */
+
+#include <linux/export.h>
+#include <linux/linkage.h>
+
+/*
+ * This is the main variant and is called by C code.  GCC's -pg option
+ * automatically instruments every C function with a call to this.
+ */
+
+	.text
+	.align		32
+	.globl		_mcount
+	.type		_mcount,#function
+	EXPORT_SYMBOL(_mcount)
+	.globl		mcount
+	.type		mcount,#function
+	EXPORT_SYMBOL(mcount)
+_mcount:
+mcount:
+#ifdef CONFIG_FUNCTION_TRACER
+#ifdef CONFIG_DYNAMIC_FTRACE
+	/* Do nothing, the retl/nop below is all we need.  */
+#else
+	sethi		%hi(ftrace_trace_function), %g1
+	sethi		%hi(ftrace_stub), %g2
+	ldx		[%g1 + %lo(ftrace_trace_function)], %g1
+	or		%g2, %lo(ftrace_stub), %g2
+	cmp		%g1, %g2
+	be,pn		%icc, 1f
+	 mov		%i7, %g3
+	save		%sp, -176, %sp
+	mov		%g3, %o1
+	jmpl		%g1, %o7
+	 mov		%i7, %o0
+	ret
+	 restore
+	/* not reached */
+1:
+#ifdef CONFIG_FUNCTION_GRAPH_TRACER
+	sethi		%hi(ftrace_graph_return), %g1
+	ldx		[%g1 + %lo(ftrace_graph_return)], %g3
+	cmp		%g2, %g3
+	bne,pn		%xcc, 5f
+	 sethi		%hi(ftrace_graph_entry_stub), %g2
+	sethi		%hi(ftrace_graph_entry), %g1
+	or		%g2, %lo(ftrace_graph_entry_stub), %g2
+	ldx		[%g1 + %lo(ftrace_graph_entry)], %g1
+	cmp		%g1, %g2
+	be,pt		%xcc, 2f
+	 nop
+5:	mov		%i7, %g2
+	mov		%fp, %g3
+	save		%sp, -176, %sp
+	mov		%g2, %l0
+	ba,pt		%xcc, ftrace_graph_caller
+	 mov		%g3, %l1
+#endif
+2:
+#endif
+#endif
+	retl
+	 nop
+	.size		_mcount,.-_mcount
+	.size		mcount,.-mcount
+
+#ifdef CONFIG_FUNCTION_TRACER
+	.globl		ftrace_stub
+	.type		ftrace_stub,#function
+ftrace_stub:
+	retl
+	 nop
+	.size		ftrace_stub,.-ftrace_stub
+#ifdef CONFIG_DYNAMIC_FTRACE
+	.globl		ftrace_caller
+	.type		ftrace_caller,#function
+ftrace_caller:
+	mov		%i7, %g2
+	mov		%fp, %g3
+	save		%sp, -176, %sp
+	mov		%g2, %o1
+	mov		%g2, %l0
+	mov		%g3, %l1
+	.globl		ftrace_call
+ftrace_call:
+	call		ftrace_stub
+	 mov		%i7, %o0
+#ifdef CONFIG_FUNCTION_GRAPH_TRACER
+	.globl		ftrace_graph_call
+ftrace_graph_call:
+	call		ftrace_stub
+	 nop
+#endif
+	ret
+	 restore
+#ifdef CONFIG_FUNCTION_GRAPH_TRACER
+	.size		ftrace_graph_call,.-ftrace_graph_call
+#endif
+	.size		ftrace_call,.-ftrace_call
+	.size		ftrace_caller,.-ftrace_caller
+#endif
+#endif
+
+#ifdef CONFIG_FUNCTION_GRAPH_TRACER
+ENTRY(ftrace_graph_caller)
+	mov		%l0, %o0
+	mov		%i7, %o1
+	call		prepare_ftrace_return
+	 mov		%l1, %o2
+	ret
+	 restore	%o0, -8, %i7
+END(ftrace_graph_caller)
+
+ENTRY(return_to_handler)
+	save		%sp, -176, %sp
+	call		ftrace_return_to_handler
+	 mov		%fp, %o0
+	jmpl		%o0 + 8, %g0
+	 restore
+END(return_to_handler)
+#endif