netdev - Re: [PATCH bpf 1/5] bpf, s390x: do not reload skb pointers in non-skb context

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Date:   Tue, 9 Jan 2018 15:20:37 +0100
From:   Michael Holzheu <holzheu@...ux.vnet.ibm.com>
To:     Daniel Borkmann <daniel@...earbox.net>
Cc:     ast@...com, naveen.n.rao@...ux.vnet.ibm.com, davem@...emloft.net,
        netdev@...r.kernel.org
Subject: Re: [PATCH bpf 1/5] bpf, s390x: do not reload skb pointers in
 non-skb context

Am Thu, 14 Dec 2017 21:07:23 +0100
schrieb Daniel Borkmann <daniel@...earbox.net>:

> The assumption of unconditionally reloading skb pointers on
> BPF helper calls where bpf_helper_changes_pkt_data() holds
> true is wrong. There can be different contexts where the
> BPF helper would enforce a reload such as in case of XDP.
> Here, we do have a struct xdp_buff instead of struct sk_buff
> as context, thus this will access garbage.
> 
> JITs only ever need to deal with cached skb pointer reload
> when ld_abs/ind was seen, therefore guard the reload behind
> SEEN_SKB only. Tested on s390x.

Hello Daniel,

Sorry for the late answer - I have been on vacation up to now.
Thanks for fixing / testing this for s390x.

Michael