Re: [PATCH bpf-next] bpf: correct slot_type marking logic to allow more stack slot sharing

[Daniel Borkmann <daniel@iogearbox.net>]

On 12/15/2018 09:34 AM, Jiong Wang wrote:
> Verifier is supposed to support sharing stack slot allocated to ptr with
> SCALAR_VALUE for privileged program. However this doesn't happen for some
> cases.
> 
> The reason is verifier is not clearing slot_type STACK_SPILL for all bytes,
> it only clears part of them, while verifier is using:
> 
>   slot_type[0] == STACK_SPILL
> 
> as a convention to check one slot is ptr type.
> 
> So, the consequence of partial clearing slot_type is verifier could treat a
> partially overridden ptr slot, which should now be a SCALAR_VALUE slot,
> still as ptr slot, and rejects some valid programs.
> 
> Before this patch, test_xdp_noinline.o under bpf selftests, bpf_lxc.o and
> bpf_netdev.o under Cilium bpf repo, when built with -mattr=+alu32 are
> rejected due to this issue. After this patch, they all accepted.
> 
> There is no processed insn number change before and after this patch on
> Cilium bpf programs.
> 
> Reviewed-by: Jakub Kicinski <jakub.kicinski@netronome.com>
> Signed-off-by: Jiong Wang <jiong.wang@netronome.com>

Reviewed-by: Daniel Borkmann <daniel@iogearbox.net>