Re: [PATCH v6 09/14] mips: Properly account for stack randomization and stack guard gap

[Alexandre Ghiti]

On 8/8/19 11:16 AM, Sergei Shtylyov wrote:
> Hello!
>
> On 08.08.2019 9:17, 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 arm here:
> > https://lkml.kernel.org/r/20170622200033.25714-1-riel@xxxxxxxxxx
> >
> > Signed-off-by: Alexandre Ghiti <alex@xxxxxxxx>
> > Acked-by: Kees Cook <keescook@xxxxxxxxxxxx>
> > Acked-by: Paul Burton <paul.burton@xxxxxxxx>
> > Reviewed-by: Luis Chamberlain <mcgrof@xxxxxxxxxx>
> > ---
> > Â arch/mips/mm/mmap.c | 14 ++++++++++++--
> > Â 1 file changed, 12 insertions(+), 2 deletions(-)
> >
> > diff --git a/arch/mips/mm/mmap.c b/arch/mips/mm/mmap.c
> > index d79f2b432318..f5c778113384 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;ÂÂÂ /* 
> > Sane caches */
> > Â EXPORT_SYMBOL(shm_align_mask);
> > Â Â /* gap between mmap and stack */
> > -#define MIN_GAP (128*1024*1024UL)
> > -#define MAX_GAP ((TASK_SIZE)/6*5)
> > +#define MIN_GAPÂÂÂÂÂÂÂ (128*1024*1024UL)
> > +#define MAX_GAPÂÂÂÂÂÂÂ ((TASK_SIZE)/6*5)
>
> ÂÂ Could add spaces around *, while touching this anyway? And parens
> around TASK_SIZE shouldn't be needed...

I did not fix checkpatch warnings here since this code gets removed 
afterwards.


> > +#define STACK_RND_MASKÂÂÂ (0x7ff >> (PAGE_SHIFT - 12))
> > Â Â static int mmap_is_legacy(struct rlimit *rlim_stack)
> > Â {
> > @@ -38,6 +39,15 @@ static int mmap_is_legacy(struct rlimit *rlim_stack)
> > Â static unsigned long mmap_base(unsigned long rnd, struct rlimit 
> > *rlim_stack)
> > Â {
> > ÂÂÂÂÂ unsigned long gap = rlim_stack->rlim_cur;
> > +ÂÂÂ unsigned long pad = stack_guard_gap;
> > +
> > +ÂÂÂ /* Account for stack randomization if necessary */
> > +ÂÂÂ if (current->flags & PF_RANDOMIZE)
> > +ÂÂÂÂÂÂÂ pad += (STACK_RND_MASK << PAGE_SHIFT);
>
> ÂÂ Parens not needed here.


Belt and braces approach here as I'm never sure about priorities.

Thanks for your time,

Alex


> > +
> > +ÂÂÂ /* Values close to RLIM_INFINITY can overflow. */
> > +ÂÂÂ if (gap + pad > gap)
> > +ÂÂÂÂÂÂÂ gap += pad;
> > Â ÂÂÂÂÂ if (gap < MIN_GAP)
> > ÂÂÂÂÂÂÂÂÂ gap = MIN_GAP;
>
>
> _______________________________________________
> linux-riscv mailing list
> linux-riscv@xxxxxxxxxxxxxxxxxxx
> http://lists.infradead.org/mailman/listinfo/linux-riscv