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, 68 insertions, 0 deletions

diff --git a/drivers/video/logo/logo.c b/drivers/video/logo/logo.c
new file mode 100644
index 000000000..91535f884
--- /dev/null
+++ b/drivers/video/logo/logo.c
@@ -0,0 +1,68 @@
+// SPDX-License-Identifier: GPL-2.0-only
+
+/*
+ *  Linux logo to be displayed on boot
+ *
+ *  Copyright (C) 1996 Larry Ewing (lewing@isc.tamu.edu)
+ *  Copyright (C) 1996,1998 Jakub Jelinek (jj@sunsite.mff.cuni.cz)
+ *  Copyright (C) 2001 Greg Banks <gnb@alphalink.com.au>
+ *  Copyright (C) 2001 Jan-Benedict Glaw <jbglaw@lug-owl.de>
+ *  Copyright (C) 2003 Geert Uytterhoeven <geert@linux-m68k.org>
+ */
+
+#include <linux/linux_logo.h>
+#include <linux/stddef.h>
+#include <linux/module.h>
+
+#ifdef CONFIG_M68K
+#include <asm/setup.h>
+#endif
+
+static bool nologo;
+module_param(nologo, bool, 0);
+MODULE_PARM_DESC(nologo, "Disables startup logo");
+
+/*
+ * Logos are located in the initdata, and will be freed in kernel_init.
+ * Use late_init to mark the logos as freed to prevent any further use.
+ */
+
+static bool logos_freed;
+
+static int __init fb_logo_late_init(void)
+{
+	logos_freed = true;
+	return 0;
+}
+
+late_initcall_sync(fb_logo_late_init);
+
+/* logo's are marked __initdata. Use __ref to tell
+ * modpost that it is intended that this function uses data
+ * marked __initdata.
+ */
+const struct linux_logo * __ref fb_find_logo(int depth)
+{
+	const struct linux_logo *logo = NULL;
+
+	if (nologo || logos_freed)
+		return NULL;
+
+#ifdef CONFIG_LOGO_LINUX_MONO
+	if (depth >= 1)
+		logo = &logo_linux_mono;
+#endif
+	
+#ifdef CONFIG_LOGO_LINUX_VGA16
+	if (depth >= 4)
+		logo = &logo_linux_vga16;
+#endif
+	
+#ifdef CONFIG_LOGO_LINUX_CLUT224
+	if (depth >= 8)
+		logo = &logo_linux_clut224;
+#endif
+
+	return logo;
+}
+EXPORT_SYMBOL_GPL(fb_find_logo);