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/admin-guide/sysctl/index.rst | 107 +++++++++++++++++++++++++++++ 1 file changed, 107 insertions(+) create mode 100644 Documentation/admin-guide/sysctl/index.rst (limited to 'Documentation/admin-guide/sysctl/index.rst') diff --git a/Documentation/admin-guide/sysctl/index.rst b/Documentation/admin-guide/sysctl/index.rst new file mode 100644 index 000000000..50f00514f --- /dev/null +++ b/Documentation/admin-guide/sysctl/index.rst @@ -0,0 +1,107 @@ +=========================== +Documentation for /proc/sys +=========================== + +Copyright (c) 1998, 1999, Rik van Riel + +------------------------------------------------------------------------------ + +'Why', I hear you ask, 'would anyone even _want_ documentation +for them sysctl files? If anybody really needs it, it's all in +the source...' + +Well, this documentation is written because some people either +don't know they need to tweak something, or because they don't +have the time or knowledge to read the source code. + +Furthermore, the programmers who built sysctl have built it to +be actually used, not just for the fun of programming it :-) + +------------------------------------------------------------------------------ + +Legal blurb: + +As usual, there are two main things to consider: + +1. you get what you pay for +2. it's free + +The consequences are that I won't guarantee the correctness of +this document, and if you come to me complaining about how you +screwed up your system because of wrong documentation, I won't +feel sorry for you. I might even laugh at you... + +But of course, if you _do_ manage to screw up your system using +only the sysctl options used in this file, I'd like to hear of +it. Not only to have a great laugh, but also to make sure that +you're the last RTFMing person to screw up. + +In short, e-mail your suggestions, corrections and / or horror +stories to: + +Rik van Riel. + +-------------------------------------------------------------- + +Introduction +============ + +Sysctl is a means of configuring certain aspects of the kernel +at run-time, and the /proc/sys/ directory is there so that you +don't even need special tools to do it! +In fact, there are only four things needed to use these config +facilities: + +- a running Linux system +- root access +- common sense (this is especially hard to come by these days) +- knowledge of what all those values mean + +As a quick 'ls /proc/sys' will show, the directory consists of +several (arch-dependent?) subdirs. Each subdir is mainly about +one part of the kernel, so you can do configuration on a piece +by piece basis, or just some 'thematic frobbing'. + +This documentation is about: + +=============== =============================================================== +abi/ execution domains & personalities +<$ARCH> tuning controls for various CPU architecture (e.g. csky, s390) +crypto/ cryptographic subsystem +debug/ debugging features +dev/ device specific information (e.g. dev/cdrom/info) +fs/ specific filesystems + filehandle, inode, dentry and quota tuning + binfmt_misc +kernel/ global kernel info / tuning + miscellaneous stuff + some architecture-specific controls + security (LSM) stuff +net/ networking stuff, for documentation look in: + +proc/ +sunrpc/ SUN Remote Procedure Call (NFS) +user/ Per user namespace limits +vm/ memory management tuning + buffer and cache management +xen/ Xen hypervisor controls +=============== =============================================================== + +These are the subdirs I have on my system or have been discovered by +searching through the source code. There might be more or other subdirs +in another setup. If you see another dir, I'd really like to hear about +it :-) + +.. toctree:: + :maxdepth: 1 + + abi + crypto + debug + fs + kernel + net + sunrpc + user + vm + xen -- cgit v1.3.1