[PATCH] arm64: mmu: Place guard page after mapping of kernel image

[Ard Biesheuvel]

On 27 July 2017 at 18:03, Will Deacon <will.deacon at arm.com> wrote:
> The vast majority of virtual allocations in the vmalloc region are followed
> by a guard page, which can help to avoid overruning on vma into another,
> which may map a read-sensitive device.
>
> This patch adds a guard page to the end of the kernel image mapping (i.e.
> following the data/bss segments).
>
> Cc: Mark Rutland <mark.rutland at arm.com>
> Cc: Ard Biesheuvel <ard.biesheuvel at linaro.org>
> Signed-off-by: Will Deacon <will.deacon at arm.com>
> ---
>  arch/arm64/mm/mmu.c | 18 +++++++++++-------
>  1 file changed, 11 insertions(+), 7 deletions(-)
>
> diff --git a/arch/arm64/mm/mmu.c b/arch/arm64/mm/mmu.c
> index 23c2d89a362e..f1eb15e0e864 100644
> --- a/arch/arm64/mm/mmu.c
> +++ b/arch/arm64/mm/mmu.c
> @@ -496,7 +496,7 @@ void mark_rodata_ro(void)
>
>  static void __init map_kernel_segment(pgd_t *pgd, void *va_start, void *va_end,
>                                       pgprot_t prot, struct vm_struct *vma,
> -                                     int flags)
> +                                     int flags, unsigned long vm_flags)
>  {
>         phys_addr_t pa_start = __pa_symbol(va_start);
>         unsigned long size = va_end - va_start;
> @@ -507,10 +507,13 @@ static void __init map_kernel_segment(pgd_t *pgd, void *va_start, void *va_end,
>         __create_pgd_mapping(pgd, pa_start, (unsigned long)va_start, size, prot,
>                              early_pgtable_alloc, flags);
>
> +       if (!(vm_flags & VM_NO_GUARD))
> +               size += PAGE_SIZE;
> +
>         vma->addr       = va_start;
>         vma->phys_addr  = pa_start;
>         vma->size       = size;
> -       vma->flags      = VM_MAP;
> +       vma->flags      = VM_MAP | vm_flags;
>         vma->caller     = __builtin_return_address(0);
>
>         vm_area_add_early(vma);
> @@ -541,14 +544,15 @@ static void __init map_kernel(pgd_t *pgd)
>          * Only rodata will be remapped with different permissions later on,
>          * all other segments are allowed to use contiguous mappings.
>          */
> -       map_kernel_segment(pgd, _text, _etext, text_prot, &vmlinux_text, 0);
> +       map_kernel_segment(pgd, _text, _etext, text_prot, &vmlinux_text, 0,
> +                          VM_NO_GUARD);
>         map_kernel_segment(pgd, __start_rodata, __inittext_begin, PAGE_KERNEL,
> -                          &vmlinux_rodata, NO_CONT_MAPPINGS);
> +                          &vmlinux_rodata, NO_CONT_MAPPINGS, VM_NO_GUARD);
>         map_kernel_segment(pgd, __inittext_begin, __inittext_end, text_prot,
> -                          &vmlinux_inittext, 0);
> +                          &vmlinux_inittext, 0, VM_NO_GUARD);
>         map_kernel_segment(pgd, __initdata_begin, __initdata_end, PAGE_KERNEL,
> -                          &vmlinux_initdata, 0);
> -       map_kernel_segment(pgd, _data, _end, PAGE_KERNEL, &vmlinux_data, 0);
> +                          &vmlinux_initdata, 0, VM_NO_GUARD);
> +       map_kernel_segment(pgd, _data, _end, PAGE_KERNEL, &vmlinux_data, 0, 0);
>
>         if (!pgd_val(*pgd_offset_raw(pgd, FIXADDR_START))) {
>                 /*

Reviewed-by: Ard Biesheuvel <ard.biesheuvel at linaro.org>