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, 40 insertions, 0 deletions

diff --git a/drivers/accessibility/speakup/serialio.h b/drivers/accessibility/speakup/serialio.h
new file mode 100644
index 000000000..b4f9a1925
--- /dev/null
+++ b/drivers/accessibility/speakup/serialio.h
@@ -0,0 +1,40 @@
+/* SPDX-License-Identifier: GPL-2.0 */
+#ifndef _SPEAKUP_SERIAL_H
+#define _SPEAKUP_SERIAL_H
+
+#include <linux/serial.h>	/* for rs_table, serial constants */
+#include <linux/serial_reg.h>	/* for more serial constants */
+#include <linux/serial_core.h>
+
+#include "spk_priv.h"
+
+/*
+ * this is cut&paste from 8250.h. Get rid of the structure, the definitions
+ * and this whole broken driver.
+ */
+struct old_serial_port {
+	unsigned int uart; /* unused */
+	unsigned int baud_base;
+	unsigned int port;
+	unsigned int irq;
+	upf_t flags; /* unused */
+};
+
+/* countdown values for serial timeouts in us */
+#define SPK_SERIAL_TIMEOUT SPK_SYNTH_TIMEOUT
+/* countdown values transmitter/dsr timeouts in us */
+#define SPK_XMITR_TIMEOUT 100000
+/* countdown values cts timeouts in us */
+#define SPK_CTS_TIMEOUT 100000
+/* check ttyS0 ... ttyS3 */
+#define SPK_LO_TTY 0
+#define SPK_HI_TTY 3
+/* # of timeouts permitted before disable */
+#define NUM_DISABLE_TIMEOUTS 3
+/* buffer timeout in ms */
+#define SPK_TIMEOUT 100
+
+#define spk_serial_tx_busy() \
+	(!uart_lsr_tx_empty(inb(speakup_info.port_tts + UART_LSR)))
+
+#endif