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The current LoongArch BPF trampoline implementation is incompatible
with tracing functions in kernel modules. This causes several severe
and user-visible problems:
* The `bpf_selftests/module_attach` test fails consistently.
* Kernel lockup when a BPF program is attached to a module function [1].
* Critical kernel modules like WireGuard experience traffic disruption
when their functions are traced with fentry [2].
Given the severity and the potential for other unknown side-effects, it
is safest to disable the feature entirely for now. This patch prevents
the BPF subsystem from allowing trampoline attachments to kernel module
functions on LoongArch.
This is a temporary mitigation until the core issues in the trampoline
code for kernel module handling can be identified and fixed.
[root@fedora bpf]# ./test_progs -a module_attach -v
bpf_testmod.ko is already unloaded.
Loading bpf_testmod.ko...
Successfully loaded bpf_testmod.ko.
test_module_attach:PASS:skel_open 0 nsec
test_module_attach:PASS:set_attach_target 0 nsec
test_module_attach:PASS:set_attach_target_explicit 0 nsec
test_module_attach:PASS:skel_load 0 nsec
libbpf: prog 'handle_fentry': failed to attach: -ENOTSUPP
libbpf: prog 'handle_fentry': failed to auto-attach: -ENOTSUPP
test_module_attach:FAIL:skel_attach skeleton attach failed: -524
Summary: 0/0 PASSED, 0 SKIPPED, 1 FAILED
Successfully unloaded bpf_testmod.ko.
[1]: https://lore.kernel.org/loongarch/CAK3+h2wDmpC-hP4u4pJY8T-yfKyk4yRzpu2LMO+C13FMT58oqQ@mail.gmail.com/
[2]: https://lore.kernel.org/loongarch/CAK3+h2wYcpc+OwdLDUBvg2rF9rvvyc5amfHT-KcFaK93uoELPg@mail.gmail.com/
Cc: stable@vger.kernel.org
Fixes: f9b6b41f0c ("LoongArch: BPF: Add basic bpf trampoline support")
Acked-by: Hengqi Chen <hengqi.chen@gmail.com>
Signed-off-by: Vincent Li <vincent.mc.li@gmail.com>
Signed-off-by: Huacai Chen <chenhuacai@loongson.cn>
Linux kernel
============
There are several guides for kernel developers and users. These guides can
be rendered in a number of formats, like HTML and PDF. Please read
Documentation/admin-guide/README.rst first.
In order to build the documentation, use ``make htmldocs`` or
``make pdfdocs``. The formatted documentation can also be read online at:
https://www.kernel.org/doc/html/latest/
There are various text files in the Documentation/ subdirectory,
several of them using the reStructuredText markup notation.
Please read the Documentation/process/changes.rst file, as it contains the
requirements for building and running the kernel, and information about
the problems which may result by upgrading your kernel.