netdev - Re: [PATCH net-next 5/5] bpf: write back the verifier log buffer as it gets filled

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Message-ID: <20171005142647.7a8d87a3@cakuba.netronome.com>
Date:   Thu, 5 Oct 2017 14:26:47 -0700
From:   Jakub Kicinski <kubakici@...pl>
To:     Daniel Borkmann <daniel@...earbox.net>
Cc:     netdev@...r.kernel.org, alexei.starovoitov@...il.com,
        oss-drivers@...ronome.com
Subject: Re: [PATCH net-next 5/5] bpf: write back the verifier log buffer as
 it gets filled

On Thu, 05 Oct 2017 23:10:03 +0200, Daniel Borkmann wrote:
> >   include/linux/bpf_verifier.h |  7 +++--
> >   kernel/bpf/verifier.c        | 64 +++++++++++++++++++++++++++++++-------------
> >   2 files changed, 50 insertions(+), 21 deletions(-)
> >
> > diff --git a/include/linux/bpf_verifier.h b/include/linux/bpf_verifier.h
> > index 598802dd1897..c0f0e210c3f8 100644
> > --- a/include/linux/bpf_verifier.h
> > +++ b/include/linux/bpf_verifier.h
> > @@ -140,10 +140,13 @@ struct bpf_verifier_env {
> >   	bool seen_direct_write;
> >   	struct bpf_insn_aux_data *insn_aux_data; /* array of per-insn state */
> >
> > -	u32 log_level;
> > +	char __user *log_ubuf;
> > +	u32 log_usize;
> > +	u32 log_ulen;
> > +	char *log_buf;
> >   	u32 log_size;
> >   	u32 log_len;
> > -	char *log_buf;
> > +	u32 log_level;  
> 
> Small request: given we'd now have log_{level,ubuf,usize,ulen,buf,size,len}
> in struct bpf_verifier_env, could we abstract that a bit e.g. into something
> like struct bpf_verifier_log, which has level and kbuf and ubuf as members
> of which {k,u}buf would be something like struct bpf_verifier_buf with three
> members (mem or buf, len_total, len_used) or such. I think most of patch 1
> is on passing env into verbose, so likely wouldn't be too much change required
> for this, but would be nice to make that a bit more structured if we need to
> touch it anyway.

I thought about it but got put off by the fact that on of the bufs has
a special __user marking..  So I don't think we can really have a common
struct bpf_verifier_buf for the two :S  Any suggestions on how to work
around that?

> >
> >   		ret = -ENOMEM;
> > -		env->log_buf = vmalloc(env->log_size);
> > +		env->log_buf = page_address(alloc_page(GFP_USER));  
> 
> alloc_page() can return NULL, if I spot this correctly, then page_address()
> cannot handle NULL and would try to deref it, no? Am I missing something?

Oh, I need to fix the nfp driver too, then!