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, 208 insertions, 0 deletions

diff --git a/drivers/video/fbdev/n411.c b/drivers/video/fbdev/n411.c
new file mode 100644
index 000000000..a36773133
--- /dev/null
+++ b/drivers/video/fbdev/n411.c
@@ -0,0 +1,208 @@
+/*
+ * linux/drivers/video/n411.c -- Platform device for N411 EPD kit
+ *
+ * Copyright (C) 2008, Jaya Kumar
+ *
+ * This file is subject to the terms and conditions of the GNU General Public
+ * License. See the file COPYING in the main directory of this archive for
+ * more details.
+ *
+ * Layout is based on skeletonfb.c by James Simmons and Geert Uytterhoeven.
+ *
+ * This driver is written to be used with the Hecuba display controller
+ * board, and tested with the EInk 800x600 display in 1 bit mode.
+ * The interface between Hecuba and the host is TTL based GPIO. The
+ * GPIO requirements are 8 writable data lines and 6 lines for control.
+ * Only 4 of the controls are actually used here but 6 for future use.
+ * The driver requires the IO addresses for data and control GPIO at
+ * load time. It is also possible to use this display with a standard
+ * PC parallel port.
+ *
+ * General notes:
+ * - User must set dio_addr=0xIOADDR cio_addr=0xIOADDR c2io_addr=0xIOADDR
+ *
+ */
+
+#include <linux/module.h>
+#include <linux/kernel.h>
+#include <linux/errno.h>
+#include <linux/string.h>
+#include <linux/delay.h>
+#include <linux/interrupt.h>
+#include <linux/fb.h>
+#include <linux/init.h>
+#include <linux/platform_device.h>
+#include <linux/list.h>
+#include <linux/uaccess.h>
+#include <linux/irq.h>
+
+#include <video/hecubafb.h>
+
+static unsigned long dio_addr;
+static unsigned long cio_addr;
+static unsigned long c2io_addr;
+static unsigned long splashval;
+static unsigned int nosplash;
+static unsigned char ctl;
+
+static void n411_set_ctl(struct hecubafb_par *par, unsigned char bit, unsigned
+							char state)
+{
+	switch (bit) {
+	case HCB_CD_BIT:
+		if (state)
+			ctl &= ~(HCB_CD_BIT);
+		else
+			ctl |= HCB_CD_BIT;
+		break;
+	case HCB_DS_BIT:
+		if (state)
+			ctl &= ~(HCB_DS_BIT);
+		else
+			ctl |= HCB_DS_BIT;
+		break;
+	}
+	outb(ctl, cio_addr);
+}
+
+static unsigned char n411_get_ctl(struct hecubafb_par *par)
+{
+	return inb(c2io_addr);
+}
+
+static void n411_set_data(struct hecubafb_par *par, unsigned char value)
+{
+	outb(value, dio_addr);
+}
+
+static void n411_wait_for_ack(struct hecubafb_par *par, int clear)
+{
+	int timeout;
+	unsigned char tmp;
+
+	timeout = 500;
+	do {
+		tmp = n411_get_ctl(par);
+		if ((tmp & HCB_ACK_BIT) && (!clear))
+			return;
+		else if (!(tmp & HCB_ACK_BIT) && (clear))
+			return;
+		udelay(1);
+	} while (timeout--);
+	printk(KERN_ERR "timed out waiting for ack\n");
+}
+
+static int n411_init_control(struct hecubafb_par *par)
+{
+	unsigned char tmp;
+	/* for init, we want the following setup to be set:
+	WUP = lo
+	ACK = hi
+	DS = hi
+	RW = hi
+	CD = lo
+	*/
+
+	/* write WUP to lo, DS to hi, RW to hi, CD to lo */
+	ctl = HCB_WUP_BIT | HCB_RW_BIT | HCB_CD_BIT ;
+	n411_set_ctl(par, HCB_DS_BIT, 1);
+
+	/* check ACK is not lo */
+	tmp = n411_get_ctl(par);
+	if (tmp & HCB_ACK_BIT) {
+		printk(KERN_ERR "Fail because ACK is already low\n");
+		return -ENXIO;
+	}
+
+	return 0;
+}
+
+
+static int n411_init_board(struct hecubafb_par *par)
+{
+	int retval;
+
+	retval = n411_init_control(par);
+	if (retval)
+		return retval;
+
+	par->send_command(par, APOLLO_INIT_DISPLAY);
+	par->send_data(par, 0x81);
+
+	/* have to wait while display resets */
+	udelay(1000);
+
+	/* if we were told to splash the screen, we just clear it */
+	if (!nosplash) {
+		par->send_command(par, APOLLO_ERASE_DISPLAY);
+		par->send_data(par, splashval);
+	}
+
+	return 0;
+}
+
+static struct hecuba_board n411_board = {
+	.owner			= THIS_MODULE,
+	.init			= n411_init_board,
+	.set_ctl		= n411_set_ctl,
+	.set_data		= n411_set_data,
+	.wait_for_ack		= n411_wait_for_ack,
+};
+
+static struct platform_device *n411_device;
+static int __init n411_init(void)
+{
+	int ret;
+	if (!dio_addr || !cio_addr || !c2io_addr) {
+		printk(KERN_WARNING "no IO addresses supplied\n");
+		return -EINVAL;
+	}
+
+	/* request our platform independent driver */
+	request_module("hecubafb");
+
+	n411_device = platform_device_alloc("hecubafb", -1);
+	if (!n411_device)
+		return -ENOMEM;
+
+	ret = platform_device_add_data(n411_device, &n411_board,
+				       sizeof(n411_board));
+	if (ret)
+		goto put_plat_device;
+
+	/* this _add binds hecubafb to n411. hecubafb refcounts n411 */
+	ret = platform_device_add(n411_device);
+
+	if (ret)
+		goto put_plat_device;
+
+	return 0;
+
+put_plat_device:
+	platform_device_put(n411_device);
+	return ret;
+}
+
+static void __exit n411_exit(void)
+{
+	platform_device_unregister(n411_device);
+}
+
+module_init(n411_init);
+module_exit(n411_exit);
+
+module_param(nosplash, uint, 0);
+MODULE_PARM_DESC(nosplash, "Disable doing the splash screen");
+module_param_hw(dio_addr, ulong, ioport, 0);
+MODULE_PARM_DESC(dio_addr, "IO address for data, eg: 0x480");
+module_param_hw(cio_addr, ulong, ioport, 0);
+MODULE_PARM_DESC(cio_addr, "IO address for control, eg: 0x400");
+module_param_hw(c2io_addr, ulong, ioport, 0);
+MODULE_PARM_DESC(c2io_addr, "IO address for secondary control, eg: 0x408");
+module_param(splashval, ulong, 0);
+MODULE_PARM_DESC(splashval, "Splash pattern: 0x00 is black, 0x01 is white");
+
+MODULE_DESCRIPTION("board driver for n411 hecuba/apollo epd kit");
+MODULE_AUTHOR("Jaya Kumar");
+MODULE_LICENSE("GPL");
+