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

[Ashwin H]

> -----Original Message-----
> From: Ashwin H
> Sent: Thursday, May 28, 2020 1:01 PM
> To: Greg KH <gregkh@xxxxxxxxxxxxxxxxxxx>
> Cc: x86@xxxxxxxxxx; dri-devel@xxxxxxxxxxxxxxxxxxxxx; intel-
> gfx@xxxxxxxxxxxxxxxxxxxxx; linux-kernel@xxxxxxxxxxxxxxx; stable@xxxxxxxxxx;
> Srivatsa Bhat <srivatsab@xxxxxxxxxx>; srivatsa@xxxxxxxxxxxxx;
> rostedt@xxxxxxxxxxx; Steven Rostedt <srostedt@xxxxxxxxxx>; Linus
> Torvalds <torvalds@xxxxxxxxxxxxxxxxxxxx>
> Subject: RE: [PATCH v4.19.x] make 'user_access_begin()' do 'access_ok()'
> 
> 
> 
> > -----Original Message-----
> > From: Greg KH <gregkh@xxxxxxxxxxxxxxxxxxx>
> > Sent: Wednesday, May 27, 2020 9:02 PM
> > To: Ashwin H <ashwinh@xxxxxxxxxx>
> > Cc: x86@xxxxxxxxxx; dri-devel@xxxxxxxxxxxxxxxxxxxxx; intel-
> > gfx@xxxxxxxxxxxxxxxxxxxxx; linux-kernel@xxxxxxxxxxxxxxx;
> > stable@xxxxxxxxxx; Srivatsa Bhat <srivatsab@xxxxxxxxxx>;
> > srivatsa@xxxxxxxxxxxxx; rostedt@xxxxxxxxxxx; Steven Rostedt
> > <srostedt@xxxxxxxxxx>; Linus Torvalds <torvalds@xxxxxxxxxxxxxxxxxxxx>
> > 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@xxxxxxxxxxxx/#t

alpha and SH had buggy implementation of access_ok

Thanks,
Ashwin

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