On Thu, Oct 06, 2016 at 04:05:53PM +0200, Jann Horn wrote: > 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. (Although, of course, most matches for seq_printf are in debugfs files or stuff that's only enabled with some DEBUG config option or so. But there are also e.g. pr_warn() users of %p that are not in debug code.)
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