LoongArch: BPF: Don't override subprog's return value

The verifier test `calls: div by 0 in subprog` triggers a panic at the
ld.bu instruction. The ld.bu insn is trying to load byte from memory
address returned by the subprog. The subprog actually set the correct
address at the a5 register (dedicated register for BPF return values).
But at commit 73c359d1d356 ("LoongArch: BPF: Sign-extend return values")
we also sign extended a5 to the a0 register (return value in LoongArch).
For function call insn, we later propagate the a0 register back to a5
register. This is right for native calls but wrong for bpf2bpf calls
which expect zero-extended return value in a5 register. So only move a0
to a5 for native calls (i.e. non-BPF_PSEUDO_CALL).

Cc: stable@vger.kernel.org
Fixes: 73c359d1d356 ("LoongArch: BPF: Sign-extend return values")
Signed-off-by: Hengqi Chen <hengqi.chen@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 a06bf89fed679c5d686f495fb5773948717e7f77..fa1500d4aa3e3a3424468b20e634709fd4c54d96 100644 (file)
--- a/arch/loongarch/net/bpf_jit.c
+++ b/arch/loongarch/net/bpf_jit.c
@@ -907,7 +907,10 @@ static int build_insn(const struct bpf_insn *insn, struct jit_ctx *ctx, bool ext
 
                move_addr(ctx, t1, func_addr);
                emit_insn(ctx, jirl, LOONGARCH_GPR_RA, t1, 0);
-               move_reg(ctx, regmap[BPF_REG_0], LOONGARCH_GPR_A0);
+
+               if (insn->src_reg != BPF_PSEUDO_CALL)
+                       move_reg(ctx, regmap[BPF_REG_0], LOONGARCH_GPR_A0);
+
                break;
 
        /* tail call */