LoongArch: BPF: Disable trampoline for kernel module function trace

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: f9b6b41f0cf3 ("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>

diff --git a/arch/loongarch/net/bpf_jit.c b/arch/loongarch/net/bpf_jit.c
index cbe53d0b7fb063351ce774948acf41a7cb2d2d3c..f97dc9936401744a0f91f893aad2ec3c62ad9513 100644 (file)
--- a/arch/loongarch/net/bpf_jit.c
+++ b/arch/loongarch/net/bpf_jit.c
@@ -1624,6 +1624,9 @@ static int __arch_prepare_bpf_trampoline(struct jit_ctx *ctx, struct bpf_tramp_i
        /* Direct jump skips 5 NOP instructions */
        else if (is_bpf_text_address((unsigned long)orig_call))
                orig_call += LOONGARCH_BPF_FENTRY_NBYTES;
+       /* Module tracing not supported - cause kernel lockups */
+       else if (is_module_text_address((unsigned long)orig_call))
+               return -ENOTSUPP;
 
        if (flags & BPF_TRAMP_F_CALL_ORIG) {
                move_addr(ctx, LOONGARCH_GPR_A0, (const u64)im);