netdev - RE: [PATCH v2 bpf-next 2/4] bpf: Track spill/fill of bounded scalars.

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Date:   Fri, 09 Oct 2020 12:49:20 -0700
From:   John Fastabend <john.fastabend@...il.com>
To:     Alexei Starovoitov <alexei.starovoitov@...il.com>,
        davem@...emloft.net
Cc:     daniel@...earbox.net, john.fastabend@...il.com,
        netdev@...r.kernel.org, bpf@...r.kernel.org, kernel-team@...com
Subject: RE: [PATCH v2 bpf-next 2/4] bpf: Track spill/fill of bounded scalars.

Alexei Starovoitov wrote:
> From: Yonghong Song <yhs@...com>
> 
> Under register pressure the llvm may spill registers with bounds into the stack.
> The verifier has to track them through spill/fill otherwise many kinds of bound
> errors will be seen. The spill/fill of induction variables was already
> happening. This patch extends this logic from tracking spill/fill of a constant
> into any bounded register. There is no need to track spill/fill of unbounded,
> since no new information will be retrieved from the stack during register fill.
> 
> Though extra stack difference could cause state pruning to be less effective, no
> adverse affects were seen from this patch on selftests and on cilium programs.
> 
> Signed-off-by: Yonghong Song <yhs@...com>
> Signed-off-by: Alexei Starovoitov <ast@...nel.org>
> Acked-by: Andrii Nakryiko <andrii@...nel.org>
> ---
>  kernel/bpf/verifier.c | 16 +++++++++++++++-
>  1 file changed, 15 insertions(+), 1 deletion(-)

LGTM and will be useful.

Acked-by: John Fastabend <john.fastabend@...il.com>