Re: [PATCH REBASE v4 05/14] arm64, mm: Make randomization selected by generic topdown mmap layout

[Alexandre Ghiti]

On 7/24/19 7:11 PM, Luis Chamberlain wrote:
> On Wed, Jul 24, 2019 at 01:58:41AM -0400, Alexandre Ghiti wrote:
> > diff --git a/mm/util.c b/mm/util.c
> > index 0781e5575cb3..16f1e56e2996 100644
> > --- a/mm/util.c
> > +++ b/mm/util.c
> > @@ -321,7 +321,15 @@ unsigned long randomize_stack_top(unsigned long stack_top)
> >   }
> >   
> >   #ifdef CONFIG_ARCH_WANT_DEFAULT_TOPDOWN_MMAP_LAYOUT
> > -#ifdef CONFIG_ARCH_HAS_ELF_RANDOMIZE
> > +unsigned long arch_randomize_brk(struct mm_struct *mm)
> > +{
> > +	/* Is the current task 32bit ? */
> > +	if (!IS_ENABLED(CONFIG_64BIT) || is_compat_task())
> > +		return randomize_page(mm->brk, SZ_32M);
> > +
> > +	return randomize_page(mm->brk, SZ_1G);
> > +}
> > +
> >   unsigned long arch_mmap_rnd(void)
> >   {
> >   	unsigned long rnd;
> > @@ -335,7 +343,6 @@ unsigned long arch_mmap_rnd(void)
> >   
> >   	return rnd << PAGE_SHIFT;
> >   }
> So arch_randomize_brk is no longer ifdef'd around
> CONFIG_ARCH_HAS_ELF_RANDOMIZE either and yet the header
> still has it. Is that intentional?

Yes, CONFIG_ARCH_WANT_DEFAULT_TOPDOWN_MMAP_LAYOUT selects 
CONFIG_ARCH_HAS_ELF_RANDOMIZE, that's what's new about v4: the generic
functions proposed in this series come with elf randomization.


Alex


>    Luis
>
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