On Thu, Mar 30, 2017 at 12:41 PM, Dave Jones <da...@codemonkey.org.uk> wrote: > On Thu, Mar 30, 2017 at 09:45:26AM -0700, Kees Cook wrote: > > On Wed, Mar 29, 2017 at 11:44 PM, Tommi Rantala > > <tommi.t.rant...@nokia.com> wrote: > > > Hi, > > > > > > Running: > > > > > > $ sudo x86info -a > > > > > > On this HP ZBook 15 G3 laptop kills the x86info process with segfault and > > > produces the following kernel BUG. > > > > > > $ git describe > > > v4.11-rc4-40-gfe82203 > > > > > > It is also reproducible with the fedora kernel: 4.9.14-200.fc25.x86_64 > > > > > > Full dmesg output here: https://pastebin.com/raw/Kur2mpZq > > > > > > [ 51.418954] usercopy: kernel memory exposure attempt detected from > > > ffff880000090000 (dma-kmalloc-256) (4096 bytes) > > > > This seems like a real exposure: the copy is attempting to read 4096 > > bytes from a 256 byte object. > > The code[1] is doing a 4k read from /dev/mem in the range 0x90000 -> 0xa0000 > According to arch/x86/mm/init.c:devmem_is_allowed, that's still valid.. > > Note that the printk is using the direct mapping address. Is that what's > being passed down to devmem_is_allowed now ? If so, that's probably what > broke.
So this is attempting to read physical memory 0x90000 -> 0xa0000, but that's somehow resolving to a virtual address that is claimed by dma-kmalloc?? I'm confused how that's happening... -Kees > > Dave > > [1] https://github.com/kernelslacker/x86info/blob/master/mptable.c -- Kees Cook Pixel Security
