Re: [PATCH v3 03/11] arm64: Consider stack randomization for mmap base only when necessary

[Alex Ghiti]

On 4/18/19 12:37 AM, Kees Cook wrote:
> On Wed, Apr 17, 2019 at 12:26 AM Alexandre Ghiti <alex@xxxxxxxx> wrote:
> > Do not offset mmap base address because of stack randomization if
> > current task does not want randomization.
> Maybe mention that this makes this logic match the existing x86 behavior too?


Ok I will add this in case of a v4.


> > Signed-off-by: Alexandre Ghiti <alex@xxxxxxxx>
> Acked-by: Kees Cook <keescook@xxxxxxxxxxxx>

Thanks !


> -Kees
>
> > ---
> >   arch/arm64/mm/mmap.c | 6 +++++-
> >   1 file changed, 5 insertions(+), 1 deletion(-)
> >
> > diff --git a/arch/arm64/mm/mmap.c b/arch/arm64/mm/mmap.c
> > index ed4f9915f2b8..ac89686c4af8 100644
> > --- a/arch/arm64/mm/mmap.c
> > +++ b/arch/arm64/mm/mmap.c
> > @@ -65,7 +65,11 @@ unsigned long arch_mmap_rnd(void)
> >   static unsigned long mmap_base(unsigned long rnd, struct rlimit *rlim_stack)
> >   {
> >          unsigned long gap = rlim_stack->rlim_cur;
> > -       unsigned long pad = (STACK_RND_MASK << PAGE_SHIFT) + stack_guard_gap;
> > +       unsigned long pad = stack_guard_gap;
> > +
> > +       /* Account for stack randomization if necessary */
> > +       if (current->flags & PF_RANDOMIZE)
> > +               pad += (STACK_RND_MASK << PAGE_SHIFT);
> >
> >          /* Values close to RLIM_INFINITY can overflow. */
> >          if (gap + pad > gap)
> > --
> > 2.20.1