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, 152 insertions, 0 deletions

diff --git a/drivers/input/serio/rpckbd.c b/drivers/input/serio/rpckbd.c
new file mode 100644
index 000000000..4d817850b
--- /dev/null
+++ b/drivers/input/serio/rpckbd.c
@@ -0,0 +1,152 @@
+// SPDX-License-Identifier: GPL-2.0-or-later
+/*
+ *  Copyright (c) 2000-2001 Vojtech Pavlik
+ *  Copyright (c) 2002 Russell King
+ */
+
+/*
+ * Acorn RiscPC PS/2 keyboard controller driver for Linux/ARM
+ */
+
+#include <linux/module.h>
+#include <linux/interrupt.h>
+#include <linux/serio.h>
+#include <linux/err.h>
+#include <linux/platform_device.h>
+#include <linux/io.h>
+#include <linux/slab.h>
+
+#include <mach/hardware.h>
+#include <asm/hardware/iomd.h>
+
+MODULE_AUTHOR("Vojtech Pavlik, Russell King");
+MODULE_DESCRIPTION("Acorn RiscPC PS/2 keyboard controller driver");
+MODULE_LICENSE("GPL");
+MODULE_ALIAS("platform:kart");
+
+struct rpckbd_data {
+	int tx_irq;
+	int rx_irq;
+};
+
+static int rpckbd_write(struct serio *port, unsigned char val)
+{
+	while (!(iomd_readb(IOMD_KCTRL) & (1 << 7)))
+		cpu_relax();
+
+	iomd_writeb(val, IOMD_KARTTX);
+
+	return 0;
+}
+
+static irqreturn_t rpckbd_rx(int irq, void *dev_id)
+{
+	struct serio *port = dev_id;
+	unsigned int byte;
+	int handled = IRQ_NONE;
+
+	while (iomd_readb(IOMD_KCTRL) & (1 << 5)) {
+		byte = iomd_readb(IOMD_KARTRX);
+
+		serio_interrupt(port, byte, 0);
+		handled = IRQ_HANDLED;
+	}
+	return handled;
+}
+
+static irqreturn_t rpckbd_tx(int irq, void *dev_id)
+{
+	return IRQ_HANDLED;
+}
+
+static int rpckbd_open(struct serio *port)
+{
+	struct rpckbd_data *rpckbd = port->port_data;
+
+	/* Reset the keyboard state machine. */
+	iomd_writeb(0, IOMD_KCTRL);
+	iomd_writeb(8, IOMD_KCTRL);
+	iomd_readb(IOMD_KARTRX);
+
+	if (request_irq(rpckbd->rx_irq, rpckbd_rx, 0, "rpckbd", port) != 0) {
+		printk(KERN_ERR "rpckbd.c: Could not allocate keyboard receive IRQ\n");
+		return -EBUSY;
+	}
+
+	if (request_irq(rpckbd->tx_irq, rpckbd_tx, 0, "rpckbd", port) != 0) {
+		printk(KERN_ERR "rpckbd.c: Could not allocate keyboard transmit IRQ\n");
+		free_irq(rpckbd->rx_irq, port);
+		return -EBUSY;
+	}
+
+	return 0;
+}
+
+static void rpckbd_close(struct serio *port)
+{
+	struct rpckbd_data *rpckbd = port->port_data;
+
+	free_irq(rpckbd->rx_irq, port);
+	free_irq(rpckbd->tx_irq, port);
+}
+
+/*
+ * Allocate and initialize serio structure for subsequent registration
+ * with serio core.
+ */
+static int rpckbd_probe(struct platform_device *dev)
+{
+	struct rpckbd_data *rpckbd;
+	struct serio *serio;
+	int tx_irq, rx_irq;
+
+	rx_irq = platform_get_irq(dev, 0);
+	if (rx_irq < 0)
+		return rx_irq;
+
+	tx_irq = platform_get_irq(dev, 1);
+	if (tx_irq < 0)
+		return tx_irq;
+
+	serio = kzalloc_obj(*serio);
+	rpckbd = kzalloc_obj(*rpckbd);
+	if (!serio || !rpckbd) {
+		kfree(rpckbd);
+		kfree(serio);
+		return -ENOMEM;
+	}
+
+	rpckbd->rx_irq = rx_irq;
+	rpckbd->tx_irq = tx_irq;
+
+	serio->id.type		= SERIO_8042;
+	serio->write		= rpckbd_write;
+	serio->open		= rpckbd_open;
+	serio->close		= rpckbd_close;
+	serio->dev.parent	= &dev->dev;
+	serio->port_data	= rpckbd;
+	strscpy(serio->name, "RiscPC PS/2 kbd port", sizeof(serio->name));
+	strscpy(serio->phys, "rpckbd/serio0", sizeof(serio->phys));
+
+	platform_set_drvdata(dev, serio);
+	serio_register_port(serio);
+	return 0;
+}
+
+static void rpckbd_remove(struct platform_device *dev)
+{
+	struct serio *serio = platform_get_drvdata(dev);
+	struct rpckbd_data *rpckbd = serio->port_data;
+
+	serio_unregister_port(serio);
+	kfree(rpckbd);
+}
+
+static struct platform_driver rpckbd_driver = {
+	.probe		= rpckbd_probe,
+	.remove		= rpckbd_remove,
+	.driver		= {
+		.name	= "kart",
+	},
+};
+module_platform_driver(rpckbd_driver);