Re: [kernel-hardening] RE: [PATCH] printk: introduce kptr_restrict level 3
From: Jann Horn
Date: Thu Oct 06 2016 - 10:06:09 EST
On Thu, Oct 06, 2016 at 01:47:47PM +0000, Roberts, William C wrote:
> > -----Original Message-----
> > From: Christoph Hellwig [mailto:hch@xxxxxxxxxxxxx]
> > Sent: Thursday, October 6, 2016 9:32 AM
> > To: Roberts, William C <william.c.roberts@xxxxxxxxx>
> > Cc: kernel-hardening@xxxxxxxxxxxxxxxxxx; corbet@xxxxxxx; linux-
> > doc@xxxxxxxxxxxxxxx; linux-kernel@xxxxxxxxxxxxxxx
> > Subject: Re: [PATCH] printk: introduce kptr_restrict level 3
> > On Wed, Oct 05, 2016 at 02:04:46PM -0400, william.c.roberts@xxxxxxxxx wrote:
> > > From: William Roberts <william.c.roberts@xxxxxxxxx>
> > >
> > > 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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