Re: [PATCH v3 06/11] arm: Use STACK_TOP when computing mmap base address

[Alex Ghiti]

On 4/18/19 1:27 AM, Kees Cook wrote:
> On Wed, Apr 17, 2019 at 12:29 AM Alexandre Ghiti <alex@xxxxxxxx> wrote:
> > mmap base address must be computed wrt stack top address, using TASK_SIZE
> > is wrong since STACK_TOP and TASK_SIZE are not equivalent.
> >
> > Signed-off-by: Alexandre Ghiti <alex@xxxxxxxx>
> > ---
> >   arch/arm/mm/mmap.c | 4 ++--
> >   1 file changed, 2 insertions(+), 2 deletions(-)
> >
> > diff --git a/arch/arm/mm/mmap.c b/arch/arm/mm/mmap.c
> > index bff3d00bda5b..0b94b674aa91 100644
> > --- a/arch/arm/mm/mmap.c
> > +++ b/arch/arm/mm/mmap.c
> > @@ -19,7 +19,7 @@
> >
> >   /* gap between mmap and stack */
> >   #define MIN_GAP                (128*1024*1024UL)
> > -#define MAX_GAP                ((TASK_SIZE)/6*5)
> > +#define MAX_GAP                ((STACK_TOP)/6*5)
> Parens around STACK_TOP aren't needed, but you'll be removing it
> entirely, so I can't complain. ;)
>
> >   #define STACK_RND_MASK (0x7ff >> (PAGE_SHIFT - 12))
> >
> >   static int mmap_is_legacy(struct rlimit *rlim_stack)
> > @@ -51,7 +51,7 @@ static unsigned long mmap_base(unsigned long rnd, struct rlimit *rlim_stack)
> >          else if (gap > MAX_GAP)
> >                  gap = MAX_GAP;
> >
> > -       return PAGE_ALIGN(TASK_SIZE - gap - rnd);
> > +       return PAGE_ALIGN(STACK_TOP - gap - rnd);
> >   }
> >
> >   /*
> > --
> > 2.20.1
> Acked-by: Kees Cook <keescook@xxxxxxxxxxxx>


Thanks !

>