netdev - Re: [PATCH bpf] bpf: report verifier bugs as warnings

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Date:   Wed, 3 Apr 2019 16:40:55 +0200
From:   Paul Chaignon <paul.chaignon@...nge.com>
To:     Alexei Starovoitov <alexei.starovoitov@...il.com>
Cc:     Daniel Borkmann <daniel@...earbox.net>,
        Alexei Starovoitov <ast@...nel.org>, netdev@...r.kernel.org,
        bpf@...r.kernel.org, Xiao Han <xiao.han@...nge.com>,
        paul.chaignon@...il.com, Martin KaFai Lau <kafai@...com>,
        Song Liu <songliubraving@...com>, Yonghong Song <yhs@...com>
Subject: Re: [PATCH bpf] bpf: report verifier bugs as warnings

On Tue, Apr 02, 2019 at 10:39:29AM -0700, Alexei Starovoitov wrote:
> On Tue, Apr 02, 2019 at 04:37:19PM +0200, Daniel Borkmann wrote:
> > On 04/02/2019 01:58 PM, Paul Chaignon wrote:
> > > Three checks for verifier bugs were introduced in commit f4d7e40 ("bpf:
> > > introduce function calls (verification)").  The bugs were reported as
> > > incorrect programs instead of kernel warnings as the present patch
> > > implements.
> > > 
> > > Signed-off-by: Paul Chaignon <paul.chaignon@...nge.com>
> > 
> > Thanks for the patch, I think these WARN_ONCE() are a bit out of context though,
> > meaning it lacks additional information about the program in kernel log once we
> > actually manage to trigger it which we'd otherwise would potentially have had with
> > the verbose() log. And from a program debugging pov, it makes it harder after this
> > patch when verification log would suggest that all is fine. Looks like we already
> > have a few WARN_ONCE() in verifier, they should probably be converted to verbose()
> > as well to be consistent. If we really want to have a kernel warn, then lets add a
> > helper macro verbose_and_warn(...) which will trigger a one-time warning, but keeps
> > the verbose log intact as well.
> 
> I think they should stay as verbose() messages and some of the WARN_ON
> should be converted to verbose().
> I don't think there is a need for verbose_and_warn().
> 

Agreed for the verbose messages; it makes sense.  I'm a bit surprised you
don't think the verifier should warn on verifier bugs though.  It already
warns for other internal bugs such as 'regno >= MAX_BPF_REG'.  Or should
these be converted to verbose() as well?