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Date:   Tue, 6 Oct 2020 20:35:20 -0700
From:   Andrii Nakryiko <>
To:     Alexei Starovoitov <>
Cc:     "David S. Miller" <>,
        Daniel Borkmann <>,
        john fastabend <>,
        Networking <>, bpf <>,
        Kernel Team <>
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
<> wrote:
> From: Yonghong Song <>
> 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 <>
> Signed-off-by: Alexei Starovoitov <>
> ---

Acked-by: Andrii Nakryiko <>

>  kernel/bpf/verifier.c | 16 +++++++++++++++-
>  1 file changed, 15 insertions(+), 1 deletion(-)


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