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, 171 insertions, 0 deletions

diff --git a/drivers/auxdisplay/ks0108.c b/drivers/auxdisplay/ks0108.c
new file mode 100644
index 000000000..51587f0fd
--- /dev/null
+++ b/drivers/auxdisplay/ks0108.c
@@ -0,0 +1,171 @@
+// SPDX-License-Identifier: GPL-2.0
+/*
+ *    Filename: ks0108.c
+ *     Version: 0.1.0
+ * Description: ks0108 LCD Controller driver
+ *     Depends: parport
+ *
+ *      Author: Copyright (C) Miguel Ojeda <ojeda@kernel.org>
+ *        Date: 2006-10-31
+ */
+
+#define pr_fmt(fmt) KBUILD_MODNAME ": " fmt
+
+#include <linux/init.h>
+#include <linux/module.h>
+#include <linux/kernel.h>
+#include <linux/delay.h>
+#include <linux/parport.h>
+#include <linux/ks0108.h>
+
+#define KS0108_NAME "ks0108"
+
+/*
+ * Module Parameters
+ */
+
+static unsigned int ks0108_port = CONFIG_KS0108_PORT;
+module_param(ks0108_port, uint, 0444);
+MODULE_PARM_DESC(ks0108_port, "Parallel port where the LCD is connected");
+
+static unsigned int ks0108_delay = CONFIG_KS0108_DELAY;
+module_param(ks0108_delay, uint, 0444);
+MODULE_PARM_DESC(ks0108_delay, "Delay between each control writing (microseconds)");
+
+/*
+ * Device
+ */
+
+static struct parport *ks0108_parport;
+static struct pardevice *ks0108_pardevice;
+
+/*
+ * ks0108 Exported Commands (don't lock)
+ *
+ *   You _should_ lock in the top driver: This functions _should not_
+ *   get race conditions in any way. Locking for each byte here would be
+ *   so slow and useless.
+ *
+ *   There are not bit definitions because they are not flags,
+ *   just arbitrary combinations defined by the documentation for each
+ *   function in the ks0108 LCD controller. If you want to know what means
+ *   a specific combination, look at the function's name.
+ *
+ *   The ks0108_writecontrol bits need to be reverted ^(0,1,3) because
+ *   the parallel port also revert them using a "not" logic gate.
+ */
+
+#define bit(n) (((unsigned char)1)<<(n))
+
+void ks0108_writedata(unsigned char byte)
+{
+	parport_write_data(ks0108_parport, byte);
+}
+
+void ks0108_writecontrol(unsigned char byte)
+{
+	udelay(ks0108_delay);
+	parport_write_control(ks0108_parport, byte ^ (bit(0) | bit(1) | bit(3)));
+}
+
+void ks0108_displaystate(unsigned char state)
+{
+	ks0108_writedata((state ? bit(0) : 0) | bit(1) | bit(2) | bit(3) | bit(4) | bit(5));
+}
+
+void ks0108_startline(unsigned char startline)
+{
+	ks0108_writedata(min_t(unsigned char, startline, 63) | bit(6) |
+			 bit(7));
+}
+
+void ks0108_address(unsigned char address)
+{
+	ks0108_writedata(min_t(unsigned char, address, 63) | bit(6));
+}
+
+void ks0108_page(unsigned char page)
+{
+	ks0108_writedata(min_t(unsigned char, page, 7) | bit(3) | bit(4) |
+			 bit(5) | bit(7));
+}
+
+EXPORT_SYMBOL_GPL(ks0108_writedata);
+EXPORT_SYMBOL_GPL(ks0108_writecontrol);
+EXPORT_SYMBOL_GPL(ks0108_displaystate);
+EXPORT_SYMBOL_GPL(ks0108_startline);
+EXPORT_SYMBOL_GPL(ks0108_address);
+EXPORT_SYMBOL_GPL(ks0108_page);
+
+/*
+ * Is the module inited?
+ */
+
+static unsigned char ks0108_inited;
+unsigned char ks0108_isinited(void)
+{
+	return ks0108_inited;
+}
+EXPORT_SYMBOL_GPL(ks0108_isinited);
+
+static void ks0108_parport_attach(struct parport *port)
+{
+	struct pardev_cb ks0108_cb;
+
+	if (port->base != ks0108_port)
+		return;
+
+	memset(&ks0108_cb, 0, sizeof(ks0108_cb));
+	ks0108_cb.flags = PARPORT_DEV_EXCL;
+	ks0108_pardevice = parport_register_dev_model(port, KS0108_NAME,
+						      &ks0108_cb, 0);
+	if (!ks0108_pardevice) {
+		pr_err("ERROR: parport didn't register new device\n");
+		return;
+	}
+	if (parport_claim(ks0108_pardevice)) {
+		pr_err("could not claim access to parport %i. Aborting.\n",
+		       ks0108_port);
+		goto err_unreg_device;
+	}
+
+	ks0108_parport = port;
+	ks0108_inited = 1;
+	return;
+
+err_unreg_device:
+	parport_unregister_device(ks0108_pardevice);
+	ks0108_pardevice = NULL;
+}
+
+static void ks0108_parport_detach(struct parport *port)
+{
+	if (port->base != ks0108_port)
+		return;
+
+	if (!ks0108_pardevice) {
+		pr_err("%s: already unregistered.\n", KS0108_NAME);
+		return;
+	}
+
+	parport_release(ks0108_pardevice);
+	parport_unregister_device(ks0108_pardevice);
+	ks0108_pardevice = NULL;
+	ks0108_parport = NULL;
+}
+
+/*
+ * Module Init & Exit
+ */
+
+static struct parport_driver ks0108_parport_driver = {
+	.name = "ks0108",
+	.match_port = ks0108_parport_attach,
+	.detach = ks0108_parport_detach,
+};
+module_parport_driver(ks0108_parport_driver);
+
+MODULE_LICENSE("GPL v2");
+MODULE_AUTHOR("Miguel Ojeda <ojeda@kernel.org>");
+MODULE_DESCRIPTION("ks0108 LCD Controller driver");
+