From 9ca3aeb9e756a0977493d8df3ac9b94e26792000 Mon Sep 17 00:00:00 2001 From: Haoran Jiang Date: Thu, 14 Aug 2025 09:34:12 +0800 Subject: [PATCH] LoongArch: BPF: Fix incorrect return pointer value in the eBPF program MIME-Version: 1.0 Content-Type: text/plain; charset=UTF-8 Content-Transfer-Encoding: 8bit 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: Haoran Jiang --- arch/loongarch/net/bpf_jit.c | 18 +++++++++++++++++- 1 file changed, 17 insertions(+), 1 deletion(-) diff --git a/arch/loongarch/net/bpf_jit.c b/arch/loongarch/net/bpf_jit.c index abfdb6bb5c382..7df067a42f368 100644 --- a/arch/loongarch/net/bpf_jit.c +++ b/arch/loongarch/net/bpf_jit.c @@ -229,8 +229,24 @@ static void __build_epilogue(struct jit_ctx *ctx, bool is_tail_call) emit_insn(ctx, addid, LOONGARCH_GPR_SP, LOONGARCH_GPR_SP, stack_adjust); if (!is_tail_call) { - /* Set return value */ + /* + * Set return value + * Check if the 64th bit in regmap[BPF_REG_0] is 1. If it is, + * the value in regmap[BPF_REG_0] is a kernel-space address. + * + * t1 = regmap[BPF_REG_0] >> 63 + * t2 = 1 + * if(t2 == t1) + * move a0 <- regmap[BPF_REG_0] + * else + * addiw a0 <- regmap[BPF_REG_0] + 0 + */ + emit_insn(ctx, srlid, LOONGARCH_GPR_T1, regmap[BPF_REG_0], 63); + emit_insn(ctx, addid, LOONGARCH_GPR_T2, LOONGARCH_GPR_ZERO, 0x1); + emit_cond_jmp(ctx, BPF_JEQ, LOONGARCH_GPR_T1, LOONGARCH_GPR_T2, 3); emit_insn(ctx, addiw, LOONGARCH_GPR_A0, regmap[BPF_REG_0], 0); + emit_uncond_jmp(ctx, 2); + move_reg(ctx, LOONGARCH_GPR_A0, regmap[BPF_REG_0]); /* Return to the caller */ emit_insn(ctx, jirl, LOONGARCH_GPR_ZERO, LOONGARCH_GPR_RA, 0); } else {