linux-kernel - Re: [PATCH net-next v2] net: bpf: make eBPF interpreter images read-only

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Message-Id: <1409694182.1034977.162882841.29AA6A80@webmail.messagingengine.com>
Date:	Tue, 02 Sep 2014 23:43:02 +0200
From:	Hannes Frederic Sowa <hannes@...essinduktion.org>
To:	Eric Dumazet <eric.dumazet@...il.com>,
	Alexei Starovoitov <ast@...mgrid.com>
Cc:	Network Development <netdev@...r.kernel.org>,
	LKML <linux-kernel@...r.kernel.org>,
	Brad Spengler <spender@...ecurity.net>,
	Daniel Borkmann <dborkman@...hat.com>,
	Kees Cook <keescook@...omium.org>
Subject: Re: [PATCH net-next v2] net: bpf: make eBPF interpreter images read-only

On Tue, Sep 2, 2014, at 23:40, Eric Dumazet wrote:
> On Tue, 2014-09-02 at 14:31 -0700, Alexei Starovoitov wrote:
> 
> > > +static inline void bpf_prog_unlock_ro(struct bpf_prog *fp)
> > > +{
> > > +       set_memory_rw((unsigned long)fp, fp->pages);
> > 
> > why rw is needed?
> > since fp is allocated with vmalloc, vfree doesn't need
> > to touch the pages to free them, no?
> 
> That assumes that vmalloc() do not have any debugging features, like
> poisoning content before freeing, to catch some use after free.
> 
> Lets be clean and safe, and give back same memory permission we had
> after vmalloc()

Yes, I agree. I just went down the kmemleak codepaths and we certainly
don't want to cause issues in there if the implementation changes one
day.

Bye,
Hannes
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