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/networking/ipv6.rst | 78 +++++++++++++++++++++++++++++++++++++++ 1 file changed, 78 insertions(+) create mode 100644 Documentation/networking/ipv6.rst (limited to 'Documentation/networking/ipv6.rst') diff --git a/Documentation/networking/ipv6.rst b/Documentation/networking/ipv6.rst new file mode 100644 index 000000000..ba09c2f2d --- /dev/null +++ b/Documentation/networking/ipv6.rst @@ -0,0 +1,78 @@ +.. SPDX-License-Identifier: GPL-2.0 + +==== +IPv6 +==== + + +Options for the ipv6 module are supplied as parameters at load time. + +Module options may be given as command line arguments to the insmod +or modprobe command, but are usually specified in either +``/etc/modules.d/*.conf`` configuration files, or in a distro-specific +configuration file. + +The available ipv6 module parameters are listed below. If a parameter +is not specified the default value is used. + +The parameters are as follows: + +disable + + Specifies whether to load the IPv6 module, but disable all + its functionality. This might be used when another module + has a dependency on the IPv6 module being loaded, but no + IPv6 addresses or operations are desired. + + The possible values and their effects are: + + 0 + IPv6 is enabled. + + This is the default value. + + 1 + IPv6 is disabled. + + No IPv6 addresses will be added to interfaces, and + it will not be possible to open an IPv6 socket. + + A reboot is required to enable IPv6. + +autoconf + + Specifies whether to enable IPv6 address autoconfiguration + on all interfaces. This might be used when one does not wish + for addresses to be automatically generated from prefixes + received in Router Advertisements. + + The possible values and their effects are: + + 0 + IPv6 address autoconfiguration is disabled on all interfaces. + + Only the IPv6 loopback address (::1) and link-local addresses + will be added to interfaces. + + 1 + IPv6 address autoconfiguration is enabled on all interfaces. + + This is the default value. + +disable_ipv6 + + Specifies whether to disable IPv6 on all interfaces. + This might be used when no IPv6 addresses are desired. + + The possible values and their effects are: + + 0 + IPv6 is enabled on all interfaces. + + This is the default value. + + 1 + IPv6 is disabled on all interfaces. + + No IPv6 addresses will be added to interfaces. + -- cgit v1.3.1