linux-kernel - Re: [mac80211] BUG_ON with current -git (4.8.0-11417-g24532f7)

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Date:   Thu, 13 Oct 2016 14:49:55 -0700
From:   Andy Lutomirski <luto@...capital.net>
To:     Johannes Berg <johannes@...solutions.net>
Cc:     Stephen Rothwell <sfr@...b.auug.org.au>,
        "linux-next@...r.kernel.org" <linux-next@...r.kernel.org>,
        Sergey Senozhatsky <sergey.senozhatsky.work@...il.com>,
        Network Development <netdev@...r.kernel.org>,
        Sergey Senozhatsky <sergey.senozhatsky@...il.com>,
        Herbert Xu <herbert@...dor.apana.org.au>,
        "David S. Miller" <davem@...emloft.net>,
        Linux Wireless List <linux-wireless@...r.kernel.org>,
        "linux-kernel@...r.kernel.org" <linux-kernel@...r.kernel.org>
Subject: Re: [mac80211] BUG_ON with current -git (4.8.0-11417-g24532f7)

On Oct 13, 2016 6:46 AM, "Johannes Berg" <johannes@...solutions.net> wrote:
>
> On Thu, 2016-10-13 at 22:42 +0900, Sergey Senozhatsky wrote:
> >
> > > > https://git.kernel.org/cgit/linux/kernel/git/luto/linux.git/commi
> > > > t/?h=x86/vmap_stack&id=0a39cfa6fbb5d5635c85253cc7d6b44b54822afd
> > > > https://git.kernel.org/cgit/linux/kernel/git/luto/linux.git/commi
> > > > t/?h=x86/vmap_stack&id=bf8cfa200b5a01383ea39fc8ce2f32909767baa8
> > >
> > > That truly sounds like something we'd rather avoid in the TX/RX
> > > paths though, which should perform well.
> >
> > didn't fix.
>
> It couldn't, since the new helpers weren't used in mac80211 in those
> patches yet.
>
> > so I finally had some time to do a better bug-reporter job.
> >
> > I added a bunch of printk-s and several virt_addr_valid()-s
> > to ieee80211_aes_ccm_encrypt().
> >
> > and right befoe the Oops I see the following report from
> > virt_addr_valid()
> >
> >
> >  FAIL: 00004100002cba02 > ffffc900802cba02 || 1 -> (00004100002cba02
> > >> 39) == 130
>
> Yeah, we already know that in this function the aad variable is on the
> stack, it explicitly is.
>
> The question, though, is why precisely that fails in the crypto code.
> Can you send the Oops report itself?
>

It's failing before that.  With CONFIG_VMAP_STACK=y, the stack may not
be physically contiguous and can't be used for DMA, so putting it in a
scatterlist is bogus in general, and the crypto code mostly wants a
scatterlist.

There are a couple (faster!) APIs for crypto that don't use
scatterlists, but I don't think AEAD works with them.

--Andy