Messages in this thread | | | Subject | Re: sudo x86info -a => kernel BUG at mm/usercopy.c:78! | From | Tommi Rantala <> | Date | Fri, 31 Mar 2017 08:40:00 +0300 |
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On 30.03.2017 23:01, Dave Jones wrote: > On Thu, Mar 30, 2017 at 12:52:31PM -0700, Kees Cook wrote: > > On Thu, Mar 30, 2017 at 12:41 PM, Dave Jones <davej@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.rantala@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... > > The only thing that I can think of would be a rogue ptr in the bios > table, but that seems unlikely. Tommi, can you put strace of x86info -mp somewhere? > That will confirm/deny whether we're at least asking the kernel to do sane things.
Indeed the bug happens when reading from /dev/mem:
https://pastebin.com/raw/ZEJGQP1X
# strace -f -y x86info -mp [...] open("/dev/mem", O_RDONLY) = 3</dev/mem> lseek(3</dev/mem>, 1038, SEEK_SET) = 1038 read(3</dev/mem>, "\300\235", 2) = 2 lseek(3</dev/mem>, 646144, SEEK_SET) = 646144 read(3</dev/mem>, "\1\0\0\0\0\0\0\0\0\0\0\0\0\0\0\0\0\0\0\0\0\0\0\0\0\0\0\0\0\0\0\0"..., 1024) = 1024 lseek(3</dev/mem>, 1043, SEEK_SET) = 1043 read(3</dev/mem>, "w\2", 2) = 2 lseek(3</dev/mem>, 645120, SEEK_SET) = 645120 read(3</dev/mem>, "\0\0\0\0\0\0\0\0\0\0\0\0\0\0\0\0\0\0\0\0\0\0\0\0\0\0\0\0\0\0\0\0"..., 1024) = 1024 lseek(3</dev/mem>, 654336, SEEK_SET) = 654336 read(3</dev/mem>, "\0\0\0\0\0\0\0\0\0\0\0\0\0\0\0\0\0\0\0\0\0\0\0\0\0\0\0\0\0\0\0\0"..., 1024) = 1024 lseek(3</dev/mem>, 983040, SEEK_SET) = 983040 read(3</dev/mem>, "IFE$\245S\0\0\1\0\0\0\0\360y\0\0\360\220\260\30\237{=\23\10\17\0000\276\17\0"..., 65536) = 65536 lseek(3</dev/mem>, 917504, SEEK_SET) = 917504 read(3</dev/mem>, "\377\377\377\377\377\377\377\377\377\377\377\377\377\377\377\377\377\377\377\377\377\377\377\377\377\377\377\377\377\377\377\377"..., 65536) = 65536 lseek(3</dev/mem>, 524288, SEEK_SET) = 524288 read(3</dev/mem>, <unfinished ...>) = ? +++ killed by SIGSEGV +++
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