Groups | Search | Server Info | Keyboard shortcuts | Login | Register [http] [https] [nntp] [nntps]

Groups > linux.kernel > #1614183

Re: sudo x86info -a => kernel BUG at mm/usercopy.c:78!

Show all headers | View raw

On Fri, Mar 31, 2017 at 10:17 AM, Dave Jones <davej@codemonkey.org.uk> 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...
>
> /dev/mem is using physical addresses that the kernel translates through the
> direct mapping.  __check_object_size seems to think that anything passed
> into it is always allocated by the kernel, but in this case, I think read_mem()
> is just passing through the direct mapping to copy_to_user.

How is ffff880000090000 both in the direct mapping and a slab object?

It would need to pass all of these checks, and be marked as PageSlab
before it could be evaluated by __check_heap_object:

        if (is_vmalloc_or_module_addr(ptr))
                return NULL;

        if (!virt_addr_valid(ptr))
                return NULL;

        page = virt_to_head_page(ptr);

        /* Check slab allocator for flags and size. */
        if (PageSlab(page))
                return __check_heap_object(ptr, n, page);


-Kees

-- 
Kees Cook
Pixel Security

Back to linux.kernel | Previous | Next — Previous in thread | Next in thread | Find similar | Unroll thread

Thread

Re: sudo x86info -a => kernel BUG at mm/usercopy.c:78! Kees Cook <keescook@chromium.org> - 2017-03-30 18:50 +0200
  Re: sudo x86info -a => kernel BUG at mm/usercopy.c:78! Laura Abbott <labbott@redhat.com> - 2017-03-30 19:30 +0200
    Re: sudo x86info -a => kernel BUG at mm/usercopy.c:78! Kees Cook <keescook@chromium.org> - 2017-03-30 19:40 +0200
      Re: sudo x86info -a => kernel BUG at mm/usercopy.c:78! Laura Abbott <labbott@redhat.com> - 2017-03-30 19:50 +0200
  Re: sudo x86info -a => kernel BUG at mm/usercopy.c:78! Mark Rutland <mark.rutland@arm.com> - 2017-03-30 19:30 +0200
  Re: sudo x86info -a => kernel BUG at mm/usercopy.c:78! Dave Jones <davej@codemonkey.org.uk> - 2017-03-30 21:50 +0200
    Re: sudo x86info -a => kernel BUG at mm/usercopy.c:78! Kees Cook <keescook@chromium.org> - 2017-03-30 22:00 +0200
      Re: sudo x86info -a => kernel BUG at mm/usercopy.c:78! Dave Jones <davej@codemonkey.org.uk> - 2017-03-30 22:10 +0200
      Re: sudo x86info -a => kernel BUG at mm/usercopy.c:78! Dave Jones <davej@codemonkey.org.uk> - 2017-03-31 19:20 +0200
        Re: sudo x86info -a => kernel BUG at mm/usercopy.c:78! Kees Cook <keescook@chromium.org> - 2017-03-31 19:40 +0200
          Re: sudo x86info -a => kernel BUG at mm/usercopy.c:78! Dave Jones <davej@codemonkey.org.uk> - 2017-03-31 20:10 +0200
            Re: sudo x86info -a => kernel BUG at mm/usercopy.c:78! Andy Lutomirski <luto@amacapital.net> - 2017-03-31 21:00 +0200
          Re: sudo x86info -a => kernel BUG at mm/usercopy.c:78! Linus Torvalds <torvalds@linux-foundation.org> - 2017-03-31 20:30 +0200
            Re: sudo x86info -a => kernel BUG at mm/usercopy.c:78! Kees Cook <keescook@chromium.org> - 2017-04-01 02:00 +0200
            Re: sudo x86info -a => kernel BUG at mm/usercopy.c:78! Kees Cook <keescook@chromium.org> - 2017-04-05 00:40 +0200
              Re: sudo x86info -a => kernel BUG at mm/usercopy.c:78! Linus Torvalds <torvalds@linux-foundation.org> - 2017-04-05 01:00 +0200
                Re: sudo x86info -a => kernel BUG at mm/usercopy.c:78! Kees Cook <keescook@chromium.org> - 2017-04-05 01:10 +0200
                Re: sudo x86info -a => kernel BUG at mm/usercopy.c:78! Linus Torvalds <torvalds@linux-foundation.org> - 2017-04-05 02:30 +0200
                Re: sudo x86info -a => kernel BUG at mm/usercopy.c:78! Kees Cook <keescook@chromium.org> - 2017-04-05 21:40 +0200

csiph-web