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bpf: allow self-xor operation

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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: 8021917293 ("bpf: add extra validation for input BPF program")
Cc: stable@dpdk.org

Acked-by: Konstantin Ananyev <konstantin.ananyev@intel.com>
Signed-off-by: Stephen Hemminger <stephen@networkplumber.org>
This commit is contained in:
Stephen Hemminger 2021-10-20 14:42:27 -07:00 committed by Thomas Monjalon
parent 8dd1a4e4ff
commit 80da61198b
1 changed files with 8 additions and 1 deletions
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9
lib/bpf/bpf_validate.c
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@ -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;