The current LoongArch BPF trampoline implementation is incompatible with tracing functions in kernel modules. This causes several severe and user-visible problems:
* Kernel lockups when a BPF program is attached to a module function [0]. * The `bpf_selftests/module_attach` test fails consistently. * Critical kernel modules like WireGuard experience traffic disruption when their functions are traced with fentry [1].
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 module functions on LoongArch.
This is a temporary mitigation until the core issues in the trampoline code for 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.
[0]: https://lore.kernel.org/loongarch/CAK3+h2wDmpC-hP4u4pJY8T-yfKyk4yRzpu2LMO+C1... [1]: https://lore.kernel.org/loongarch/CAK3+h2wYcpc+OwdLDUBvg2rF9rvvyc5amfHT-KcFa...
Cc: stable@vger.kernel.org Fixes: f9b6b41f0cf3 (“LoongArch: BPF: Add basic bpf trampoline support”) Closes: https://lore.kernel.org/loongarch/CAK3+h2wDmpC-hP4u4pJY8T-yfKyk4yRzpu2LMO+C1... Acked-by: Hengqi Chen hengqi.chen@gmail.com Signed-off-by: Vincent Li vincent.mc.li@gmail.com --- arch/loongarch/net/bpf_jit.c | 3 +++ 1 file changed, 3 insertions(+)
diff --git a/arch/loongarch/net/bpf_jit.c b/arch/loongarch/net/bpf_jit.c index cbe53d0b7fb0..49c1d4b95404 100644 --- 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 - causes 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);