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, 49 insertions, 0 deletions

diff --git a/arch/um/drivers/chan.h b/arch/um/drivers/chan.h
new file mode 100644
index 000000000..5a61db512
--- /dev/null
+++ b/arch/um/drivers/chan.h
@@ -0,0 +1,49 @@
+/* SPDX-License-Identifier: GPL-2.0 */
+/* 
+ * Copyright (C) 2000, 2001 Jeff Dike (jdike@karaya.com)
+ */
+
+#ifndef __CHAN_KERN_H__
+#define __CHAN_KERN_H__
+
+#include <linux/tty.h>
+#include <linux/list.h>
+#include <linux/console.h>
+#include "chan_user.h"
+#include "line.h"
+
+struct chan {
+	struct list_head list;
+	struct list_head free_list;
+	struct line *line;
+	char *dev;
+	unsigned int primary:1;
+	unsigned int input:1;
+	unsigned int output:1;
+	unsigned int opened:1;
+	unsigned int enabled:1;
+	int fd_in;
+	int fd_out; /* only different to fd_in if blocking output is needed */
+	const struct chan_ops *ops;
+	void *data;
+};
+
+extern void chan_interrupt(struct line *line, int irq);
+extern int parse_chan_pair(char *str, struct line *line, int device,
+			   const struct chan_opts *opts, char **error_out);
+extern int write_chan(struct chan *chan, const u8 *buf, size_t len,
+			     int write_irq);
+extern int console_write_chan(struct chan *chan, const char *buf, 
+			      int len);
+extern int console_open_chan(struct line *line, struct console *co);
+extern void deactivate_chan(struct chan *chan, int irq);
+extern void chan_enable_winch(struct chan *chan, struct tty_port *port);
+extern int enable_chan(struct line *line);
+extern void close_chan(struct line *line);
+extern int chan_window_size(struct line *line, 
+			     unsigned short *rows_out, 
+			     unsigned short *cols_out);
+extern int chan_config_string(struct line *line, char *str, int size,
+			      char **error_out);
+
+#endif