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

commit 60f3caff1492e5b8616b9578c4bedb5c0a88ed14 upstream.

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>
Signed-off-by: Greg Kroah-Hartman <gregkh@linuxfoundation.org>

diff --git a/arch/loongarch/net/bpf_jit.c b/arch/loongarch/net/bpf_jit.c
index 5f26ad6e0780ea1d4dfc222d8db1cd646a7a940e..a06f077673d00401b9675c269c999770043c12a1 100644 (file)
--- a/arch/loongarch/net/bpf_jit.c
+++ b/arch/loongarch/net/bpf_jit.c
@@ -844,7 +844,10 @@ 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 */