From: Dave Jones <davej@codemonkey.org.uk>
To: Kees Cook <keescook@chromium.org>
Cc: Tommi Rantala <tommi.t.rantala@nokia.com>,
Linux-MM <linux-mm@kvack.org>,
LKML <linux-kernel@vger.kernel.org>,
Laura Abbott <labbott@redhat.com>, Ingo Molnar <mingo@kernel.org>,
Josh Poimboeuf <jpoimboe@redhat.com>,
Mark Rutland <mark.rutland@arm.com>,
Eric Biggers <ebiggers@google.com>
Subject: Re: sudo x86info -a => kernel BUG at mm/usercopy.c:78!
Date: Thu, 30 Mar 2017 16:01:00 -0400 [thread overview]
Message-ID: <20170330200100.zcyndf3kimepg77o@codemonkey.org.uk> (raw)
In-Reply-To: <CAGXu5jK8=g8rBx1J4+gC8-3nwRLe2Va89hHX=S-P6SvvgiVb9A@mail.gmail.com>
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.
Dave
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next prev parent reply other threads:[~2017-03-30 20:01 UTC|newest]
Thread overview: 24+ messages / expand[flat|nested] mbox.gz Atom feed top
2017-03-30 6:44 Tommi Rantala
2017-03-30 16:45 ` Kees Cook
2017-03-30 17:20 ` Mark Rutland
2017-03-30 17:27 ` Laura Abbott
2017-03-30 17:37 ` Kees Cook
2017-03-30 17:44 ` Laura Abbott
2017-03-31 5:44 ` Tommi Rantala
2017-03-30 19:41 ` Dave Jones
2017-03-30 19:52 ` Kees Cook
2017-03-30 20:01 ` Dave Jones [this message]
2017-03-31 5:40 ` Tommi Rantala
2017-03-31 6:59 ` Tommi Rantala
2017-03-31 17:17 ` Dave Jones
2017-03-31 17:32 ` Kees Cook
2017-03-31 18:03 ` Dave Jones
2017-03-31 18:57 ` Andy Lutomirski
2017-03-31 18:26 ` Linus Torvalds
2017-03-31 19:32 ` Tommi Rantala
2017-04-04 22:37 ` Kees Cook
2017-04-04 22:55 ` Linus Torvalds
2017-04-04 22:59 ` Kees Cook
2017-04-05 0:22 ` Linus Torvalds
2017-04-05 19:39 ` Kees Cook
2017-03-31 23:58 ` Kees Cook
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