netdev - Re: [PATCH bpf-next 2/3] bpf: Track spill/fill of bounded scalars.

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Message-ID: <CAEf4BzZ-jWrWQPvd7CNOwxhi9s7d6QJq4P+ZoKGa0Pr-0yQ_Vw@mail.gmail.com>
Date:   Tue, 6 Oct 2020 20:35:20 -0700
From:   Andrii Nakryiko <andrii.nakryiko@...il.com>
To:     Alexei Starovoitov <alexei.starovoitov@...il.com>
Cc:     "David S. Miller" <davem@...emloft.net>,
        Daniel Borkmann <daniel@...earbox.net>,
        john fastabend <john.fastabend@...il.com>,
        Networking <netdev@...r.kernel.org>, bpf <bpf@...r.kernel.org>,
        Kernel Team <kernel-team@...com>
Subject: Re: [PATCH bpf-next 2/3] bpf: Track spill/fill of bounded scalars.

On Tue, Oct 6, 2020 at 1:10 PM Alexei Starovoitov
<alexei.starovoitov@...il.com> 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(-)
>

[...]