netdev - Re: [PATCH net 0/4] bpf: fix semantics issues with helpers receiving NULL arguments

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Date:   Wed, 22 Nov 2017 23:04:50 +0100
From:   Daniel Borkmann <daniel@...earbox.net>
To:     Gianluca Borello <g.borello@...il.com>, netdev@...r.kernel.org
Cc:     ast@...nel.org, yhs@...com
Subject: Re: [PATCH net 0/4] bpf: fix semantics issues with helpers receiving
 NULL arguments

On 11/22/2017 07:32 PM, Gianluca Borello wrote:
> This set includes some fixes in semantics and usability issues that emerged
> recently, and would be good to have them in net before the next release.
> 
> In particular, ARG_CONST_SIZE_OR_ZERO semantics was recently changed in
> commit 9fd29c08e520 ("bpf: improve verifier ARG_CONST_SIZE_OR_ZERO
> semantics") with the goal of letting the compiler generate simpler code
> that the verifier can more easily accept.
> 
> To handle this change in semantics, a few checks in some helpers were
> added, like in commit 9c019e2bc4b2 ("bpf: change helper bpf_probe_read arg2
> type to ARG_CONST_SIZE_OR_ZERO"), and those checks are less than ideal
> because once they make it into a released kernel bpf programs can start
> relying on them, preventing the possibility of being removed later on.
> 
> This patch tries to fix the issue by introducing a new argument type
> ARG_PTR_TO_MEM_OR_NULL that can be used for helpers that can receive a
> <NULL, 0> tuple. By doing so, we can fix the semantics of the other helpers
> that don't need <NULL, 0> and can just handle <!NULL, 0>, allowing the code
> to get rid of those checks.

Series applied to bpf tree, thanks Gianluca!