On 09/11/2015 02:25 AM, Tycho Andersen wrote:
Instead of always emitting BPF_REG_X, let's emit BPF_REG_X only when the
source actually is BPF_X. This causes programs generated by the classic
converter to not be importable via bpf(), as the eBPF verifier checks that
the src_reg is correct or 0. While not a problem yet, this will be a
problem when BPF_PROG_DUMP lands, and we can potentially dump and re-import
programs generated by the converter.
Signed-off-by: Tycho Andersen <[email protected]>
CC: Alexei Starovoitov <[email protected]>
CC: Daniel Borkmann <[email protected]>
I think the description at the beginning could have been a bit clearer. I.e.
it's safe to zero insn->src_reg for BPF_SRC(fp->code) that is not X, because
we can either have X or K for classic jump compares, and in case of K we're
only interested in the immediate value, but not a possible src_reg, of course,
so eBPF converter should have zeroed it.
Yeah, it was never really the aim of the converter to cover something like
that requirement you seem to have:
load classic BPF
-> transform into eBPF
-> dump that eBPF result to uspace
-> load that eBPF via bpf(2)
Anyway, it doesn't cause an issue in the current code as stated, but it's good
if we fix it up nevertheless.
Looks good to me:
Acked-by: Daniel Borkmann <[email protected]>
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