From 80da61198b6be66ab16964eb0944c79c0325c40e Mon Sep 17 00:00:00 2001 From: Stephen Hemminger Date: Wed, 20 Oct 2021 14:42:27 -0700 Subject: [PATCH] bpf: allow self-xor operation Some BPF programs may use XOR of a register with itself as a way to zero register in one instruction. The BPF filter converter generates this in the prolog to the generated code. The BPF validator would not allow this because the value of register was undefined. But after this operation it always zero. Fixes: 8021917293d0 ("bpf: add extra validation for input BPF program") Cc: stable@dpdk.org Acked-by: Konstantin Ananyev Signed-off-by: Stephen Hemminger --- lib/bpf/bpf_validate.c | 9 ++++++++- 1 file changed, 8 insertions(+), 1 deletion(-) diff --git a/lib/bpf/bpf_validate.c b/lib/bpf/bpf_validate.c index 7b1291b382..853279fee5 100644 --- a/lib/bpf/bpf_validate.c +++ b/lib/bpf/bpf_validate.c @@ -661,8 +661,15 @@ eval_alu(struct bpf_verifier *bvf, const struct ebpf_insn *ins) op = BPF_OP(ins->code); + /* Allow self-xor as way to zero register */ + if (op == BPF_XOR && BPF_SRC(ins->code) == BPF_X && + ins->src_reg == ins->dst_reg) { + eval_fill_imm(&rs, UINT64_MAX, 0); + eval_fill_imm(rd, UINT64_MAX, 0); + } + err = eval_defined((op != EBPF_MOV) ? rd : NULL, - (op != BPF_NEG) ? &rs : NULL); + (op != BPF_NEG) ? &rs : NULL); if (err != NULL) return err; -- 2.20.1