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, 169 insertions, 0 deletions

diff --git a/drivers/auxdisplay/cfag12864bfb.c b/drivers/auxdisplay/cfag12864bfb.c
new file mode 100644
index 000000000..24baf6b2c
--- /dev/null
+++ b/drivers/auxdisplay/cfag12864bfb.c
@@ -0,0 +1,169 @@
+// SPDX-License-Identifier: GPL-2.0
+/*
+ *    Filename: cfag12864bfb.c
+ *     Version: 0.1.0
+ * Description: cfag12864b LCD framebuffer driver
+ *     Depends: cfag12864b
+ *
+ *      Author: Copyright (C) Miguel Ojeda <ojeda@kernel.org>
+ *        Date: 2006-10-31
+ */
+
+#include <linux/init.h>
+#include <linux/module.h>
+#include <linux/kernel.h>
+#include <linux/errno.h>
+#include <linux/fb.h>
+#include <linux/mm.h>
+#include <linux/platform_device.h>
+#include <linux/cfag12864b.h>
+
+#define CFAG12864BFB_NAME "cfag12864bfb"
+
+static const struct fb_fix_screeninfo cfag12864bfb_fix = {
+	.id = "cfag12864b",
+	.type = FB_TYPE_PACKED_PIXELS,
+	.visual = FB_VISUAL_MONO10,
+	.xpanstep = 0,
+	.ypanstep = 0,
+	.ywrapstep = 0,
+	.line_length = CFAG12864B_WIDTH / 8,
+	.accel = FB_ACCEL_NONE,
+};
+
+static const struct fb_var_screeninfo cfag12864bfb_var = {
+	.xres = CFAG12864B_WIDTH,
+	.yres = CFAG12864B_HEIGHT,
+	.xres_virtual = CFAG12864B_WIDTH,
+	.yres_virtual = CFAG12864B_HEIGHT,
+	.bits_per_pixel = 1,
+	.red = { 0, 1, 0 },
+	.green = { 0, 1, 0 },
+	.blue = { 0, 1, 0 },
+	.left_margin = 0,
+	.right_margin = 0,
+	.upper_margin = 0,
+	.lower_margin = 0,
+	.vmode = FB_VMODE_NONINTERLACED,
+};
+
+static int cfag12864bfb_mmap(struct fb_info *info, struct vm_area_struct *vma)
+{
+	struct page *pages = virt_to_page(cfag12864b_buffer);
+
+	vma->vm_page_prot = pgprot_decrypted(vma->vm_page_prot);
+
+	return vm_map_pages_zero(vma, &pages, 1);
+}
+
+static const struct fb_ops cfag12864bfb_ops = {
+	.owner = THIS_MODULE,
+	__FB_DEFAULT_SYSMEM_OPS_RDWR,
+	__FB_DEFAULT_SYSMEM_OPS_DRAW,
+	.fb_mmap = cfag12864bfb_mmap,
+};
+
+static int cfag12864bfb_probe(struct platform_device *device)
+{
+	int ret = -EINVAL;
+	struct fb_info *info = framebuffer_alloc(0, &device->dev);
+
+	if (!info)
+		goto none;
+
+	info->flags = FBINFO_VIRTFB;
+	info->screen_buffer = cfag12864b_buffer;
+	info->screen_size = CFAG12864B_SIZE;
+	info->fbops = &cfag12864bfb_ops;
+	info->fix = cfag12864bfb_fix;
+	info->var = cfag12864bfb_var;
+	info->pseudo_palette = NULL;
+	info->par = NULL;
+
+	if (register_framebuffer(info) < 0)
+		goto fballoced;
+
+	platform_set_drvdata(device, info);
+
+	fb_info(info, "%s frame buffer device\n", info->fix.id);
+
+	return 0;
+
+fballoced:
+	framebuffer_release(info);
+
+none:
+	return ret;
+}
+
+static void cfag12864bfb_remove(struct platform_device *device)
+{
+	struct fb_info *info = platform_get_drvdata(device);
+
+	if (info) {
+		unregister_framebuffer(info);
+		framebuffer_release(info);
+	}
+}
+
+static struct platform_driver cfag12864bfb_driver = {
+	.probe	= cfag12864bfb_probe,
+	.remove = cfag12864bfb_remove,
+	.driver = {
+		.name	= CFAG12864BFB_NAME,
+	},
+};
+
+static struct platform_device *cfag12864bfb_device;
+
+static int __init cfag12864bfb_init(void)
+{
+	int ret = -EINVAL;
+
+	/* cfag12864b_init() must be called first */
+	if (!cfag12864b_isinited()) {
+		printk(KERN_ERR CFAG12864BFB_NAME ": ERROR: "
+			"cfag12864b is not initialized\n");
+		goto none;
+	}
+
+	if (cfag12864b_enable()) {
+		printk(KERN_ERR CFAG12864BFB_NAME ": ERROR: "
+			"can't enable cfag12864b refreshing (being used)\n");
+		return -ENODEV;
+	}
+
+	ret = platform_driver_register(&cfag12864bfb_driver);
+
+	if (!ret) {
+		cfag12864bfb_device =
+			platform_device_alloc(CFAG12864BFB_NAME, 0);
+
+		if (cfag12864bfb_device)
+			ret = platform_device_add(cfag12864bfb_device);
+		else
+			ret = -ENOMEM;
+
+		if (ret) {
+			platform_device_put(cfag12864bfb_device);
+			platform_driver_unregister(&cfag12864bfb_driver);
+		}
+	}
+
+none:
+	return ret;
+}
+
+static void __exit cfag12864bfb_exit(void)
+{
+	platform_device_unregister(cfag12864bfb_device);
+	platform_driver_unregister(&cfag12864bfb_driver);
+	cfag12864b_disable();
+}
+
+module_init(cfag12864bfb_init);
+module_exit(cfag12864bfb_exit);
+
+MODULE_LICENSE("GPL v2");
+MODULE_AUTHOR("Miguel Ojeda <ojeda@kernel.org>");
+MODULE_DESCRIPTION("cfag12864b LCD framebuffer driver");