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, 304 insertions, 0 deletions

diff --git a/drivers/usb/serial/console.c b/drivers/usb/serial/console.c
new file mode 100644
index 000000000..29f091908
--- /dev/null
+++ b/drivers/usb/serial/console.c
@@ -0,0 +1,304 @@
+// SPDX-License-Identifier: GPL-2.0
+/*
+ * USB Serial Console driver
+ *
+ * Copyright (C) 2001 - 2002 Greg Kroah-Hartman (greg@kroah.com)
+ *
+ * Thanks to Randy Dunlap for the original version of this code.
+ *
+ */
+
+#define pr_fmt(fmt) KBUILD_MODNAME ": " fmt
+
+#include <linux/kernel.h>
+#include <linux/module.h>
+#include <linux/slab.h>
+#include <linux/tty.h>
+#include <linux/console.h>
+#include <linux/serial.h>
+#include <linux/usb.h>
+#include <linux/usb/serial.h>
+
+struct usbcons_info {
+	int			magic;
+	int			break_flag;
+	struct usb_serial_port	*port;
+};
+
+static struct usbcons_info usbcons_info;
+static struct console usbcons;
+
+/*
+ * ------------------------------------------------------------
+ * USB Serial console driver
+ *
+ * Much of the code here is copied from drivers/char/serial.c
+ * and implements a phony serial console in the same way that
+ * serial.c does so that in case some software queries it,
+ * it will get the same results.
+ *
+ * Things that are different from the way the serial port code
+ * does things, is that we call the lower level usb-serial
+ * driver code to initialize the device, and we set the initial
+ * console speeds based on the command line arguments.
+ * ------------------------------------------------------------
+ */
+
+static const struct tty_operations usb_console_fake_tty_ops = {
+};
+
+/*
+ * The parsing of the command line works exactly like the
+ * serial.c code, except that the specifier is "ttyUSB" instead
+ * of "ttyS".
+ */
+static int usb_console_setup(struct console *co, char *options)
+{
+	struct usbcons_info *info = &usbcons_info;
+	int baud = 9600;
+	int bits = 8;
+	int parity = 'n';
+	int doflow = 0;
+	int cflag = CREAD | HUPCL | CLOCAL;
+	char *s;
+	struct usb_serial *serial;
+	struct usb_serial_port *port;
+	int retval;
+	struct tty_struct *tty = NULL;
+	struct ktermios dummy;
+
+	if (options) {
+		baud = simple_strtoul(options, NULL, 10);
+		s = options;
+		while (*s >= '0' && *s <= '9')
+			s++;
+		if (*s)
+			parity = *s++;
+		if (*s)
+			bits   = *s++ - '0';
+		if (*s)
+			doflow = (*s++ == 'r');
+	}
+
+	/* Sane default */
+	if (baud == 0)
+		baud = 9600;
+
+	switch (bits) {
+	case 7:
+		cflag |= CS7;
+		break;
+	default:
+	case 8:
+		cflag |= CS8;
+		break;
+	}
+	switch (parity) {
+	case 'o': case 'O':
+		cflag |= PARODD;
+		break;
+	case 'e': case 'E':
+		cflag |= PARENB;
+		break;
+	}
+
+	if (doflow)
+		cflag |= CRTSCTS;
+
+	/*
+	 * no need to check the index here: if the index is wrong, console
+	 * code won't call us
+	 */
+	port = usb_serial_port_get_by_minor(co->index);
+	if (port == NULL) {
+		/* no device is connected yet, sorry :( */
+		pr_err("No USB device connected to ttyUSB%i\n", co->index);
+		return -ENODEV;
+	}
+	serial = port->serial;
+
+	retval = usb_autopm_get_interface(serial->interface);
+	if (retval)
+		goto error_get_interface;
+
+	tty_port_tty_set(&port->port, NULL);
+
+	info->port = port;
+
+	++port->port.count;
+	if (!tty_port_initialized(&port->port)) {
+		if (serial->type->set_termios) {
+			/*
+			 * allocate a fake tty so the driver can initialize
+			 * the termios structure, then later call set_termios to
+			 * configure according to command line arguments
+			 */
+			tty = kzalloc_obj(*tty);
+			if (!tty) {
+				retval = -ENOMEM;
+				goto reset_open_count;
+			}
+			kref_init(&tty->kref);
+			tty->driver = usb_serial_tty_driver;
+			tty->index = co->index;
+			init_ldsem(&tty->ldisc_sem);
+			spin_lock_init(&tty->files_lock);
+			INIT_LIST_HEAD(&tty->tty_files);
+			kref_get(&tty->driver->kref);
+			__module_get(tty->driver->owner);
+			tty->ops = &usb_console_fake_tty_ops;
+			tty_init_termios(tty);
+			tty_port_tty_set(&port->port, tty);
+		}
+
+		/* only call the device specific open if this
+		 * is the first time the port is opened */
+		retval = serial->type->open(NULL, port);
+		if (retval) {
+			dev_err(&port->dev, "could not open USB console port\n");
+			goto fail;
+		}
+
+		if (serial->type->set_termios) {
+			tty->termios.c_cflag = cflag;
+			tty_termios_encode_baud_rate(&tty->termios, baud, baud);
+			memset(&dummy, 0, sizeof(struct ktermios));
+			serial->type->set_termios(tty, port, &dummy);
+
+			tty_port_tty_set(&port->port, NULL);
+			tty_save_termios(tty);
+			tty_kref_put(tty);
+		}
+		tty_port_set_initialized(&port->port, true);
+	}
+	/* Now that any required fake tty operations are completed restore
+	 * the tty port count */
+	--port->port.count;
+	/* The console is special in terms of closing the device so
+	 * indicate this port is now acting as a system console. */
+	port->port.console = 1;
+
+	mutex_unlock(&serial->disc_mutex);
+	return retval;
+
+ fail:
+	tty_port_tty_set(&port->port, NULL);
+	tty_kref_put(tty);
+ reset_open_count:
+	port->port.count = 0;
+	info->port = NULL;
+	usb_autopm_put_interface(serial->interface);
+ error_get_interface:
+	mutex_unlock(&serial->disc_mutex);
+	usb_serial_put(serial);
+	return retval;
+}
+
+static void usb_console_write(struct console *co,
+					const char *buf, unsigned count)
+{
+	static struct usbcons_info *info = &usbcons_info;
+	struct usb_serial_port *port = info->port;
+	struct usb_serial *serial;
+	int retval = -ENODEV;
+
+	if (!port || port->serial->dev->state == USB_STATE_NOTATTACHED)
+		return;
+	serial = port->serial;
+
+	if (count == 0)
+		return;
+
+	dev_dbg(&port->dev, "%s - %d byte(s)\n", __func__, count);
+
+	if (!port->port.console) {
+		dev_dbg(&port->dev, "%s - port not opened\n", __func__);
+		return;
+	}
+
+	while (count) {
+		unsigned int i;
+		unsigned int lf;
+		/* search for LF so we can insert CR if necessary */
+		for (i = 0, lf = 0 ; i < count ; i++) {
+			if (*(buf + i) == 10) {
+				lf = 1;
+				i++;
+				break;
+			}
+		}
+		/* pass on to the driver specific version of this function if
+		   it is available */
+		retval = serial->type->write(NULL, port, buf, i);
+		dev_dbg(&port->dev, "%s - write: %d\n", __func__, retval);
+		if (lf) {
+			/* append CR after LF */
+			unsigned char cr = 13;
+			retval = serial->type->write(NULL, port, &cr, 1);
+			dev_dbg(&port->dev, "%s - write cr: %d\n",
+							__func__, retval);
+		}
+		buf += i;
+		count -= i;
+	}
+}
+
+static struct tty_driver *usb_console_device(struct console *co, int *index)
+{
+	struct tty_driver **p = (struct tty_driver **)co->data;
+
+	if (!*p)
+		return NULL;
+
+	*index = co->index;
+	return *p;
+}
+
+static struct console usbcons = {
+	.name =		"ttyUSB",
+	.write =	usb_console_write,
+	.device =	usb_console_device,
+	.setup =	usb_console_setup,
+	.flags =	CON_PRINTBUFFER,
+	.index =	-1,
+	.data = 	&usb_serial_tty_driver,
+};
+
+void usb_serial_console_disconnect(struct usb_serial *serial)
+{
+	if (serial->port[0] && serial->port[0] == usbcons_info.port) {
+		usb_serial_console_exit();
+		usb_serial_put(serial);
+	}
+}
+
+void usb_serial_console_init(int minor)
+{
+	if (minor == 0) {
+		/*
+		 * Call register_console() if this is the first device plugged
+		 * in.  If we call it earlier, then the callback to
+		 * console_setup() will fail, as there is not a device seen by
+		 * the USB subsystem yet.
+		 */
+		/*
+		 * Register console.
+		 * NOTES:
+		 * console_setup() is called (back) immediately (from
+		 * register_console). console_write() is called immediately
+		 * from register_console iff CON_PRINTBUFFER is set in flags.
+		 */
+		pr_debug("registering the USB serial console.\n");
+		register_console(&usbcons);
+	}
+}
+
+void usb_serial_console_exit(void)
+{
+	if (usbcons_info.port) {
+		unregister_console(&usbcons);
+		usbcons_info.port->port.console = 0;
+		usbcons_info.port = NULL;
+	}
+}
+