Re: [PATCH v3 08/11] mips: Properly account for stack randomization and stack guard gap

[Alex Ghiti]

On 4/18/19 5:27 PM, Paul Burton wrote:
> Hi Alexandre,
>
> On Wed, Apr 17, 2019 at 01:22:44AM -0400, Alexandre Ghiti wrote:
> > This commit takes care of stack randomization and stack guard gap when
> > computing mmap base address and checks if the task asked for randomization.
> > This fixes the problem uncovered and not fixed for mips here:
> > https://www.mail-archive.com/linux-kernel@xxxxxxxxxxxxxxx/msg1429066.html
> >
> > Signed-off-by: Alexandre Ghiti <alex@xxxxxxxx>
> For patches 8-10:
>
>      Acked-by: Paul Burton <paul.burton@xxxxxxxx>
>
> Thanks for improving this,


Thank you for your time,


Alex


>      Paul
>
> > ---
> >   arch/mips/mm/mmap.c | 14 ++++++++++++--
> >   1 file changed, 12 insertions(+), 2 deletions(-)
> >
> > diff --git a/arch/mips/mm/mmap.c b/arch/mips/mm/mmap.c
> > index 2f616ebeb7e0..3ff82c6f7e24 100644
> > --- a/arch/mips/mm/mmap.c
> > +++ b/arch/mips/mm/mmap.c
> > @@ -21,8 +21,9 @@ unsigned long shm_align_mask = PAGE_SIZE - 1;	/* Sane caches */
> >   EXPORT_SYMBOL(shm_align_mask);
> >   
> >   /* gap between mmap and stack */
> > -#define MIN_GAP (128*1024*1024UL)
> > -#define MAX_GAP ((TASK_SIZE)/6*5)
> > +#define MIN_GAP		(128*1024*1024UL)
> > +#define MAX_GAP		((TASK_SIZE)/6*5)
> > +#define STACK_RND_MASK	(0x7ff >> (PAGE_SHIFT - 12))
> >   
> >   static int mmap_is_legacy(struct rlimit *rlim_stack)
> >   {
> > @@ -38,6 +39,15 @@ static int mmap_is_legacy(struct rlimit *rlim_stack)
> >   static unsigned long mmap_base(unsigned long rnd, struct rlimit *rlim_stack)
> >   {
> >   	unsigned long gap = rlim_stack->rlim_cur;
> > +	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)
> > +		gap += pad;
> >   
> >   	if (gap < MIN_GAP)
> >   		gap = MIN_GAP;
> > --
> > 2.20.1
> _______________________________________________
> linux-riscv mailing list
> linux-riscv@xxxxxxxxxxxxxxxxxxx
> http://lists.infradead.org/mailman/listinfo/linux-riscv