[dpdk-dev] [PATCH v4 2/8] bpf: allow self-xor operation
From: Stephen Hemminger <stephen@networkplumber.org>
Date: 2021-09-08 17:17:02
Subsystem:
library code, the rest · Maintainers:
Andrew Morton, Linus Torvalds
When doing BPF filter program conversion, a common way
to zero a register in single instruction is:
xor r7,r7
The BPF validator would not allow this because the value of
r7 was undefined. But after this operation it always zero.
Signed-off-by: Stephen Hemminger <stephen@networkplumber.org>
---
lib/bpf/bpf_validate.c | 8 ++++++--
1 file changed, 6 insertions(+), 2 deletions(-)
diff --git a/lib/bpf/bpf_validate.c b/lib/bpf/bpf_validate.c
index 7b1291b382e9..7647a7454dc2 100644
--- a/lib/bpf/bpf_validate.c
+++ b/lib/bpf/bpf_validate.c@@ -661,8 +661,12 @@ eval_alu(struct bpf_verifier *bvf, const struct ebpf_insn *ins) op = BPF_OP(ins->code); - err = eval_defined((op != EBPF_MOV) ? rd : NULL, - (op != BPF_NEG) ? &rs : NULL); + /* Allow self-xor as way to zero register */ + if (op == BPF_XOR && ins->src_reg == ins->dst_reg) + err = NULL; + else + err = eval_defined((op != EBPF_MOV) ? rd : NULL, + (op != BPF_NEG) ? &rs : NULL); if (err != NULL) return err;
--
2.30.2