From a5f7a5bb3b7f28ba7e4fa246775b29a0e5537255 Mon Sep 17 00:00:00 2001 From: Jinke Han Date: Tue, 8 Sep 2026 15:37:42 +0800 Subject: x86/kprobes: Fix crash when probing CS CALL instructions 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) Signed-off-by: Jinke Han Signed-off-by: Ingo Molnar Reviewed-by: Masami Hiramatsu (Google) Acked-by: Yafang Shao Acked-by: Borislav Petkov Cc: Peter Zijlstra Link: https://patch.msgid.link/20260908073742.GA10517@didi-ThinkCentre-M920t-N000 --- Documentation/driver-api/frame-buffer.rst | 62 +++++++++++++++++++++++++++++++ 1 file changed, 62 insertions(+) create mode 100644 Documentation/driver-api/frame-buffer.rst (limited to 'Documentation/driver-api/frame-buffer.rst') diff --git a/Documentation/driver-api/frame-buffer.rst b/Documentation/driver-api/frame-buffer.rst new file mode 100644 index 000000000..9dd3060f0 --- /dev/null +++ b/Documentation/driver-api/frame-buffer.rst @@ -0,0 +1,62 @@ +Frame Buffer Library +==================== + +The frame buffer drivers depend heavily on four data structures. These +structures are declared in include/linux/fb.h. They are fb_info, +fb_var_screeninfo, fb_fix_screeninfo and fb_monospecs. The last +three can be made available to and from userland. + +fb_info defines the current state of a particular video card. Inside +fb_info, there exists a fb_ops structure which is a collection of +needed functions to make fbdev and fbcon work. fb_info is only visible +to the kernel. + +fb_var_screeninfo is used to describe the features of a video card +that are user defined. With fb_var_screeninfo, things such as depth +and the resolution may be defined. + +The next structure is fb_fix_screeninfo. This defines the properties +of a card that are created when a mode is set and can't be changed +otherwise. A good example of this is the start of the frame buffer +memory. This "locks" the address of the frame buffer memory, so that it +cannot be changed or moved. + +The last structure is fb_monospecs. In the old API, there was little +importance for fb_monospecs. This allowed for forbidden things such as +setting a mode of 800x600 on a fix frequency monitor. With the new API, +fb_monospecs prevents such things, and if used correctly, can prevent a +monitor from being cooked. fb_monospecs will not be useful until +kernels 2.5.x. + +Frame Buffer Memory +------------------- + +.. kernel-doc:: drivers/video/fbdev/core/fbmem.c + :export: + +Frame Buffer Colormap +--------------------- + +.. kernel-doc:: drivers/video/fbdev/core/fbcmap.c + :export: + +Frame Buffer Video Mode Database +-------------------------------- + +.. kernel-doc:: drivers/video/fbdev/core/modedb.c + :internal: + +.. kernel-doc:: drivers/video/fbdev/core/modedb.c + :export: + +Frame Buffer Macintosh Video Mode Database +------------------------------------------ + +.. kernel-doc:: drivers/video/fbdev/macmodes.c + :export: + +Frame Buffer Fonts +------------------ + +Refer to the file lib/fonts/fonts.c for more information. + -- cgit v1.3.1