RE: [PATCH v4.19.x] make 'user_access_begin()' do 'access_ok()'

Ashwin H
2020-05-28T11:20:44Z

> -----Original Message-----
> From: Ashwin H
> Sent: Thursday, May 28, 2020 1:01 PM
> To: Greg KH <gregkh@linuxfoundation.org>
> Cc: x86@kernel.org; dri-devel@lists.freedesktop.org; intel-
> gfx@lists.freedesktop.org; linux-kernel@vger.kernel.org; stable@kernel.org;
> Srivatsa Bhat <srivatsab@vmware.com>; srivatsa@csail.mit.edu;
> rostedt@goodmis.org; Steven Rostedt <srostedt@vmware.com>; Linus
> Torvalds <torvalds@linux-foundation.org>
> Subject: RE: [PATCH v4.19.x] make 'user_access_begin()' do 'access_ok()'
>
>
>
> > -----Original Message-----
> > From: Greg KH <gregkh@linuxfoundation.org>
> > Sent: Wednesday, May 27, 2020 9:02 PM
> > To: Ashwin H <ashwinh@vmware.com>
> > Cc: x86@kernel.org; dri-devel@lists.freedesktop.org; intel-
> > gfx@lists.freedesktop.org; linux-kernel@vger.kernel.org;
> > stable@kernel.org; Srivatsa Bhat <srivatsab@vmware.com>;
> > srivatsa@csail.mit.edu; rostedt@goodmis.org; Steven Rostedt
> > <srostedt@vmware.com>; Linus Torvalds <torvalds@linux-foundation.org>
> > Subject: Re: [PATCH v4.19.x] make 'user_access_begin()' do 'access_ok()'
> >
> > On Wed, May 13, 2020 at 05:08:19PM +0000, Ashwin H wrote:
> > > > Ok, but what does that mean for us?
> > > >
> > > > You need to say why you are sending a patch, otherwise we will
> > > > guess
> > wrong.
> > >
> > > In drivers/gpu/drm/i915/i915_gem_execbuffer.c, ioctl functions does
> > user_access_begin() without doing access_ok(Checks if a user space
> > pointer is valid) first.
> > > A local attacker can craft a malicious ioctl function call to
> > > overwrite arbitrary kernel memory, resulting in a Denial of Service
> > > or privilege escalation (CVE-2018-20669)
> > >
> > > This patch makes sure that user_access_begin always does access_ok.
> > > user_access_begin has been modified to do access_ok internally.
> >
> > I had this in the tree, but it broke the build on alpha, sh, and maybe
> > a few others :(
> >
> Thanks Greg for including this patch.
> I am sorry that this patch caused the failure. As I see this is not a build failure
> but tests have failed.
> Build results:
> total: 155 pass: 155 fail: 0
> Qemu test results:
> total: 421 pass: 390 fail: 31
> Failed tests:
> <all alpha>
> <all sh>
> <all sheb>
>
> > See:
> > https://nam04.safelinks.protection.outlook.com/?url=https%3A%2F
> > %2Flore.kernel.org%2Fr%2F20200527140225.GA214763%40roeck-
> >
> us.net&amp;data=02%7C01%7Cashwinh%40vmware.com%7Cd8f60bb8a4584
> >
> 7caa10f08d802530997%7Cb39138ca3cee4b4aa4d6cd83d9dd62f0%7C0%7C0%7
> >
> C637261902960990057&amp;sdata=Vjv9v0QhebfcOGSq1UUDKshTDA%2FOV
> > 4aKbqzKKJkEQxM%3D&amp;reserved=0
> > for the details.
> >
> > Can you dig out all of the needed follow-on patches as well, and send
> > them all as a patch series for 4.19.y so that I can queue them all up at once?
> >
>
> I will check for follow-on patches and get back.

This seems to be the issue in alpha and SH
https://lore.kernel.org/lkml/6a4fe075-a644-1b06-305b-9e55b8c9575b@roeck-us.net/#t

alpha and SH had buggy implementation of access_ok

Thanks,
Ashwin

>
> > thanks,
> >
> > greg k-h
>
> Thanks,
> Ashwin