Re: [PATCH v3 10/11] mips: Use generic mmap top-down layout

[Kees Cook]

On Wed, Apr 17, 2019 at 12:33 AM Alexandre Ghiti <alex@xxxxxxxx> wrote:
>
> mips uses a top-down layout by default that fits the generic functions.
> At the same time, this commit allows to fix 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>

Acked-by: Kees Cook <keescook@xxxxxxxxxxxx>

-Kees

> ---
>  arch/mips/Kconfig                 |  1 +
>  arch/mips/include/asm/processor.h |  5 ---
>  arch/mips/mm/mmap.c               | 67 -------------------------------
>  3 files changed, 1 insertion(+), 72 deletions(-)
>
> diff --git a/arch/mips/Kconfig b/arch/mips/Kconfig
> index 4a5f5b0ee9a9..ec2f07561e4d 100644
> --- a/arch/mips/Kconfig
> +++ b/arch/mips/Kconfig
> @@ -14,6 +14,7 @@ config MIPS
>         select ARCH_USE_CMPXCHG_LOCKREF if 64BIT
>         select ARCH_USE_QUEUED_RWLOCKS
>         select ARCH_USE_QUEUED_SPINLOCKS
> +       select ARCH_WANT_DEFAULT_TOPDOWN_MMAP_LAYOUT if MMU
>         select ARCH_WANT_IPC_PARSE_VERSION
>         select BUILDTIME_EXTABLE_SORT
>         select CLONE_BACKWARDS
> diff --git a/arch/mips/include/asm/processor.h b/arch/mips/include/asm/processor.h
> index aca909bd7841..fba18d4a9190 100644
> --- a/arch/mips/include/asm/processor.h
> +++ b/arch/mips/include/asm/processor.h
> @@ -29,11 +29,6 @@
>
>  extern unsigned int vced_count, vcei_count;
>
> -/*
> - * MIPS does have an arch_pick_mmap_layout()
> - */
> -#define HAVE_ARCH_PICK_MMAP_LAYOUT 1
> -
>  #ifdef CONFIG_32BIT
>  #ifdef CONFIG_KVM_GUEST
>  /* User space process size is limited to 1GB in KVM Guest Mode */
> diff --git a/arch/mips/mm/mmap.c b/arch/mips/mm/mmap.c
> index ffbe69f3a7d9..61e65a69bb09 100644
> --- a/arch/mips/mm/mmap.c
> +++ b/arch/mips/mm/mmap.c
> @@ -20,43 +20,6 @@
>  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                ((STACK_TOP)/6*5)
> -#define STACK_RND_MASK (0x7ff >> (PAGE_SHIFT - 12))
> -
> -static int mmap_is_legacy(struct rlimit *rlim_stack)
> -{
> -       if (current->personality & ADDR_COMPAT_LAYOUT)
> -               return 1;
> -
> -       if (rlim_stack->rlim_cur == RLIM_INFINITY)
> -               return 1;
> -
> -       return sysctl_legacy_va_layout;
> -}
> -
> -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;
> -       else if (gap > MAX_GAP)
> -               gap = MAX_GAP;
> -
> -       return PAGE_ALIGN(STACK_TOP - gap - rnd);
> -}
> -
>  #define COLOUR_ALIGN(addr, pgoff)                              \
>         ((((addr) + shm_align_mask) & ~shm_align_mask) +        \
>          (((pgoff) << PAGE_SHIFT) & shm_align_mask))
> @@ -154,36 +117,6 @@ unsigned long arch_get_unmapped_area_topdown(struct file *filp,
>                         addr0, len, pgoff, flags, DOWN);
>  }
>
> -unsigned long arch_mmap_rnd(void)
> -{
> -       unsigned long rnd;
> -
> -#ifdef CONFIG_COMPAT
> -       if (TASK_IS_32BIT_ADDR)
> -               rnd = get_random_long() & ((1UL << mmap_rnd_compat_bits) - 1);
> -       else
> -#endif /* CONFIG_COMPAT */
> -               rnd = get_random_long() & ((1UL << mmap_rnd_bits) - 1);
> -
> -       return rnd << PAGE_SHIFT;
> -}
> -
> -void arch_pick_mmap_layout(struct mm_struct *mm, struct rlimit *rlim_stack)
> -{
> -       unsigned long random_factor = 0UL;
> -
> -       if (current->flags & PF_RANDOMIZE)
> -               random_factor = arch_mmap_rnd();
> -
> -       if (mmap_is_legacy(rlim_stack)) {
> -               mm->mmap_base = TASK_UNMAPPED_BASE + random_factor;
> -               mm->get_unmapped_area = arch_get_unmapped_area;
> -       } else {
> -               mm->mmap_base = mmap_base(random_factor, rlim_stack);
> -               mm->get_unmapped_area = arch_get_unmapped_area_topdown;
> -       }
> -}
> -
>  static inline unsigned long brk_rnd(void)
>  {
>         unsigned long rnd = get_random_long();
> --
> 2.20.1
>


-- 
Kees Cook