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); Actually, I think I missed something here. We don't really want to censor pointers in dmesg, right? dmesg can contain pointers by design - and in particular, when an oops happens, the register dump will reveal pointers. dmesg should just be restricted using dmesg_restrict. (What is annoying, though, is that e.g. Debian's default rsyslog config sends all KERN_EMERG messages to all active PTYs by default, meaning that on a system with such a config, making the kernel oops can be used to leak some ASLR information.) (And why does __die() in arch/x86/kernel/dumpstack.c use KERN_EMERG for CONFIG_X86_32, but KERN_ALERT for !CONFIG_X86_32?)
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