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Date: Thu, 6 Oct 2016 16:05:53 +0200
From: Jann Horn <jann@...jh.net>
To: "Roberts, William C" <william.c.roberts@...el.com>
Cc: Christoph Hellwig <hch@...radead.org>,
"kernel-hardening@...ts.openwall.com" <kernel-hardening@...ts.openwall.com>,
"corbet@....net" <corbet@....net>,
"linux-doc@...r.kernel.org" <linux-doc@...r.kernel.org>,
"linux-kernel@...r.kernel.org" <linux-kernel@...r.kernel.org>
Subject: Re: RE: [PATCH] printk: introduce kptr_restrict
level 3
On Thu, Oct 06, 2016 at 01:47:47PM +0000, Roberts, William C wrote:
> > -----Original Message-----
> > From: Christoph Hellwig [mailto:hch@...radead.org]
> > Sent: Thursday, October 6, 2016 9:32 AM
> > To: Roberts, William C <william.c.roberts@...el.com>
> > Cc: kernel-hardening@...ts.openwall.com; corbet@....net; linux-
> > doc@...r.kernel.org; linux-kernel@...r.kernel.org
> > Subject: Re: [PATCH] printk: introduce kptr_restrict level 3
> >
> > On Wed, Oct 05, 2016 at 02:04:46PM -0400, william.c.roberts@...el.com wrote:
> > > From: William Roberts <william.c.roberts@...el.com>
> > >
> > > Some out-of-tree modules do not use %pK and just use %p, as it's the
> > > common C paradigm for printing pointers. Because of this,
> > > kptr_restrict has no affect on the output and thus, no way to contain
> > > the kernel address leak.
> >
> > So what? We a) don't care about out of tree modules and b) you could just triviall
> > fix them up if you care.
>
> Out of tree modules still affect core kernel security. I would also bet money, that somewhere
> In-tree someone has put a %p when they wanted a %pK. So this method is just quite error
> prone. We currently have a blacklist approach versus whitelist.
grep says you have a point:
$ grep -IR 'seq_printf.*%p[^FfSsBRrhbMmIiEUVKNadCDgG].*&'
drivers/dma/qcom/hidma_dbg.c: seq_printf(s, "dev_trca=%p\n", &dmadev->dev_trca);
drivers/dma/qcom/hidma_dbg.c: seq_printf(s, "dev_evca=%p\n", &dmadev->dev_evca);
$ grep -IR 'pr_info.*%p[^FfSsBRrhbMmIiEUVKNadCDgG].*&'
drivers/misc/lkdtm_heap.c: pr_info("Allocated memory %p-%p\n", base, &base[offset * 2]);
$ grep -IR 'pr_err.*%p[^FfSsBRrhbMmIiEUVKNadCDgG].*&'
drivers/net/ethernet/qlogic/qlge/qlge_dbg.c: pr_err("rx_ring->cqicb = %p\n", &rx_ring->cqicb);
And these are just trivially greppable, low-hanging-fruit ones.
With somewhat broader greps, there seem to be lots more, but they'd
require manual review.
And in total, there are 13578 matches for %p[^FfSsBRrhbMmIiEUVKNadCDgG]
throughout the kernel. Reviewing all of those manually would suck.
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