lkml.org 
[lkml]   [2011]   [Jul]   [24]   [last100]   RSS Feed
Views: [wrap][no wrap]   [headers]  [forward] 
 
Messages in this thread
/
Date
From
SubjectRe: [PATCH] x86, AMD: Correct F15h IC aliasing issue
On Sun, Jul 24, 2011 at 02:30:46PM -0400, Ingo Molnar wrote:
> > > So I really think that you might be *much* better off just changing
> > > mmap_rnd(), and nothing else. Just make *that* mask off the three low
> > > bits of the random address, ie something like
> > >
> > > diff --git a/arch/x86/mm/mmap.c b/arch/x86/mm/mmap.c
> > > index 1dab5194fd9d..6b62ab5a5ae1 100644
> > > --- a/arch/x86/mm/mmap.c
> > > +++ b/arch/x86/mm/mmap.c
> > > @@ -90,6 +90,9 @@ static unsigned long mmap_rnd(void)
> > > rnd = (long)get_random_int() % (1<<8);
> > > else
> > > rnd = (long)(get_random_int() % (1<<28));
> > > +
> > > + if (avoid_aliasing_in_bits_14_12)
> > > + rnd &= ~7;
> > > }
> > > return rnd << PAGE_SHIFT;
> > > }
> > >
> > > would be fundamentally very safe - it would already take all our
> > > current anti-randomization code into account.
> > >
> > > No?
> >
> > Hehe, we had that idea initially. However, the special 1% case I was
> > hinting at is this:
> >
> > process P0, mapping libraries A, B, C
> >
> > and
> >
> > process P1, mapping libraries A, C
> >
> > Library C ends up possibly with aliasing VAs and there's the
> > problem again. [...]
>
> Well, since all library positions are randomized, and the quirk masks
> out bits 12,13,14, all libraries that are not explicitly fix-mapped
> will end up on a 32K granular VA address.

Right, but IIUC, mmap_rnd() is used to determine mm->mmap_base so the
mmap starting address will have [14:12] cleared but the initial address
of library C's mapping in the example above will possibly differ in
those bits due to different linking order, right?

> Also, in practice on most distros most libraries will be prelinked to
> the same address in all processes.

I think at least on RHEL there's a daemon doing prelinking every two
weeks or so...

--
Regards/Gruss,
Boris.

Advanced Micro Devices GmbH
Einsteinring 24, 85609 Dornach
GM: Alberto Bozzo
Reg: Dornach, Landkreis Muenchen
HRB Nr. 43632 WEEE Registernr: 129 19551


\
 
 \ /
  Last update: 2011-07-24 21:11    [W:0.182 / U:0.092 seconds]
©2003-2020 Jasper Spaans|hosted at Digital Ocean and TransIP|Read the blog|Advertise on this site