Re: [PATCH v2] LoongArch: BPF: Fix incorrect return pointer value in the eBPF program

[Daniel Borkmann <daniel@xxxxxxxxxxxxx>]

On 8/15/25 10:29 AM, Haoran Jiang wrote:
> In some eBPF programs, the return value is a pointer.
> When the kernel call an eBPF program (such as struct_ops),
> it expects a 64-bit address to be returned, but instead a 32-bit value.
>
> Before applying this patch:
> ./test_progs -a ns_bpf_qdisc
> CPU 7 Unable to handle kernel paging request at virtual
> address 0000000010440158.
>
> As shown in the following test case,
> bpf_fifo_dequeue return value is a pointer.
> progs/bpf_qdisc_fifo.c
>
> SEC("struct_ops/bpf_fifo_dequeue")
> struct sk_buff *BPF_PROG(bpf_fifo_dequeue, struct Qdisc *sch)
> {
> 	struct sk_buff *skb = NULL;
> 	........
> 	skb = bpf_kptr_xchg(&skbn->skb, skb);
> 	........
> 	return skb;
> }
>
> kernel call bpf_fifo_dequeue：
> net/sched/sch_generic.c
>
> static struct sk_buff *dequeue_skb(struct Qdisc *q, bool *validate,
> 				   int *packets)
> {
> 	struct sk_buff *skb = NULL;
> 	........
> 	skb = q->dequeue(q);
> 	.........
> }
> When accessing the skb, an address exception error will occur.
> because the value returned by q->dequeue at this point is a 32-bit
> address rather than a 64-bit address.
>
> After applying the patch：
> ./test_progs -a ns_bpf_qdisc
> Warning: sch_htb: quantum of class 10001 is small. Consider r2q change.
> 213/1   ns_bpf_qdisc/fifo:OK
> 213/2   ns_bpf_qdisc/fq:OK
> 213/3   ns_bpf_qdisc/attach to mq:OK
> 213/4   ns_bpf_qdisc/attach to non root:OK
> 213/5   ns_bpf_qdisc/incompl_ops:OK
> 213     ns_bpf_qdisc:OK
> Summary: 1/5 PASSED, 0 SKIPPED, 0 FAILED
>
> Fixes: 73c359d1d356 ("LoongArch: BPF: Sign-extend return values")
> Signed-off-by: Jinyang He <hejinyang@xxxxxxxxxxx>
> Signed-off-by: Haoran Jiang <jianghaoran@xxxxxxxxxx>

Huacai, are you routing the fix or want us to route via bpf tree?

Thanks,
Daniel