Re: [PATCH] x86/mm: Enable KASLR for vmemmap memory region (x86_64)

[Thomas Garnier <thgarnie@google.com>]

On Wed, Jul 27, 2016 at 8:59 AM, Thomas Garnier <thgarnie@google.com> wrote:
> Add vmemmap in the list of randomized memory regions.
>
> The vmemmap region holds a representation of the physical memory (through
> a struct page array). An attacker could use this region to disclose the
> kernel memory layout (walking the page linked list).
>
> Signed-off-by: Thomas Garnier <thgarnie@google.com>
> Signed-off-by: Kees Cook <keescook@chromium.org>
> ---
> Missing patch didn't pick-up by the tip bot on KASLR memory randomization.
> Resending after rebase on tip and tests as discussed with Ingo.
> Based on tip 4bcc8cf6ab5932cbb2511c8e18065e61b069f21c

Ingo: Any comment? Can you integrate it on tip?

> ---
>  arch/x86/include/asm/kaslr.h            |  1 +
>  arch/x86/include/asm/pgtable_64_types.h |  4 +++-
>  arch/x86/mm/kaslr.c                     | 24 +++++++++++++++++++++++-
>  3 files changed, 27 insertions(+), 2 deletions(-)
>
> diff --git a/arch/x86/include/asm/kaslr.h b/arch/x86/include/asm/kaslr.h
> index 2674ee3..1052a79 100644
> --- a/arch/x86/include/asm/kaslr.h
> +++ b/arch/x86/include/asm/kaslr.h
> @@ -6,6 +6,7 @@ unsigned long kaslr_get_random_long(const char *purpose);
>  #ifdef CONFIG_RANDOMIZE_MEMORY
>  extern unsigned long page_offset_base;
>  extern unsigned long vmalloc_base;
> +extern unsigned long vmemmap_base;
>
>  void kernel_randomize_memory(void);
>  #else
> diff --git a/arch/x86/include/asm/pgtable_64_types.h b/arch/x86/include/asm/pgtable_64_types.h
> index 6fdef9e..3a26420 100644
> --- a/arch/x86/include/asm/pgtable_64_types.h
> +++ b/arch/x86/include/asm/pgtable_64_types.h
> @@ -57,11 +57,13 @@ typedef struct { pteval_t pte; } pte_t;
>  #define MAXMEM         _AC(__AC(1, UL) << MAX_PHYSMEM_BITS, UL)
>  #define VMALLOC_SIZE_TB        _AC(32, UL)
>  #define __VMALLOC_BASE _AC(0xffffc90000000000, UL)
> -#define VMEMMAP_START  _AC(0xffffea0000000000, UL)
> +#define __VMEMMAP_BASE _AC(0xffffea0000000000, UL)
>  #ifdef CONFIG_RANDOMIZE_MEMORY
>  #define VMALLOC_START  vmalloc_base
> +#define VMEMMAP_START  vmemmap_base
>  #else
>  #define VMALLOC_START  __VMALLOC_BASE
> +#define VMEMMAP_START  __VMEMMAP_BASE
>  #endif /* CONFIG_RANDOMIZE_MEMORY */
>  #define VMALLOC_END    (VMALLOC_START + _AC((VMALLOC_SIZE_TB << 40) - 1, UL))
>  #define MODULES_VADDR    (__START_KERNEL_map + KERNEL_IMAGE_SIZE)
> diff --git a/arch/x86/mm/kaslr.c b/arch/x86/mm/kaslr.c
> index 26dccd6..3e9875f 100644
> --- a/arch/x86/mm/kaslr.c
> +++ b/arch/x86/mm/kaslr.c
> @@ -44,13 +44,22 @@
>   * ensure that this order is correct and won't be changed.
>   */
>  static const unsigned long vaddr_start = __PAGE_OFFSET_BASE;
> -static const unsigned long vaddr_end = VMEMMAP_START;
> +
> +#if defined(CONFIG_X86_ESPFIX64)
> +static const unsigned long vaddr_end = ESPFIX_BASE_ADDR;
> +#elif defined(CONFIG_EFI)
> +static const unsigned long vaddr_end = EFI_VA_START;
> +#else
> +static const unsigned long vaddr_end = __START_KERNEL_map;
> +#endif
>
>  /* Default values */
>  unsigned long page_offset_base = __PAGE_OFFSET_BASE;
>  EXPORT_SYMBOL(page_offset_base);
>  unsigned long vmalloc_base = __VMALLOC_BASE;
>  EXPORT_SYMBOL(vmalloc_base);
> +unsigned long vmemmap_base = __VMEMMAP_BASE;
> +EXPORT_SYMBOL(vmemmap_base);
>
>  /*
>   * Memory regions randomized by KASLR (except modules that use a separate logic
> @@ -63,6 +72,7 @@ static __initdata struct kaslr_memory_region {
>  } kaslr_regions[] = {
>         { &page_offset_base, 64/* Maximum */ },
>         { &vmalloc_base, VMALLOC_SIZE_TB },
> +       { &vmemmap_base, 1 },
>  };
>
>  /* Get size in bytes used by the memory region */
> @@ -89,6 +99,18 @@ void __init kernel_randomize_memory(void)
>         struct rnd_state rand_state;
>         unsigned long remain_entropy;
>
> +       /*
> +        * All these BUILD_BUG_ON checks ensures the memory layout is
> +        * consistent with the vaddr_start/vaddr_end variables.
> +        */
> +       BUILD_BUG_ON(vaddr_start >= vaddr_end);
> +       BUILD_BUG_ON(config_enabled(CONFIG_X86_ESPFIX64) &&
> +                    vaddr_end >= EFI_VA_START);
> +       BUILD_BUG_ON((config_enabled(CONFIG_X86_ESPFIX64) ||
> +                     config_enabled(CONFIG_EFI)) &&
> +                    vaddr_end >= __START_KERNEL_map);
> +       BUILD_BUG_ON(vaddr_end > __START_KERNEL_map);
> +
>         if (!kaslr_memory_enabled())
>                 return;
>
> --
> 2.8.0.rc3.226.g39d4020
>