linux-kernel - Re: [PATCH v2 7/9] get the random phy addr according to slot

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Date:	Wed, 4 Mar 2015 13:28:32 -0800
From:	Kees Cook <keescook@...omium.org>
To:	Baoquan He <bhe@...hat.com>
Cc:	"H. Peter Anvin" <hpa@...or.com>, Yinghai Lu <yinghai@...nel.org>,
	Vivek Goyal <vgoyal@...hat.com>,
	Andy Lutomirski <luto@...capital.net>,
	Andrew Morton <akpm@...ux-foundation.org>,
	Thomas Gleixner <tglx@...utronix.de>,
	Ingo Molnar <mingo@...hat.com>,
	LKML <linux-kernel@...r.kernel.org>
Subject: Re: [PATCH v2 7/9] get the random phy addr according to slot_area info

On Mon, Mar 2, 2015 at 6:58 AM, Baoquan He <bhe@...hat.com> wrote:
> Now random value can be used to get related slot info stored in
> slot_area, mainly use slot_area.num to position which slot is target.
> With this slot its starting address is returned as the physical
> address where kernel will put.
>
> Signed-off-by: Baoquan He <bhe@...hat.com>
> ---
>  arch/x86/boot/compressed/aslr.c | 34 +++++++++++++++++++---------------
>  1 file changed, 19 insertions(+), 15 deletions(-)
>
> diff --git a/arch/x86/boot/compressed/aslr.c b/arch/x86/boot/compressed/aslr.c
> index 1c6fb31..55adee2 100644
> --- a/arch/x86/boot/compressed/aslr.c
> +++ b/arch/x86/boot/compressed/aslr.c
> @@ -245,9 +245,6 @@ static unsigned long mem_min_overlap(struct mem_vector *img, struct mem_vector *
>         return min;
>  }
>
> -static unsigned long slots[CONFIG_RANDOMIZE_BASE_MAX_OFFSET /
> -                          CONFIG_PHYSICAL_ALIGN];
> -
>  struct slot_area {
>         unsigned long addr;
>         int num;
> @@ -261,23 +258,28 @@ static unsigned long slot_max;
>
>  static unsigned long slot_area_index;
>
> -static void slots_append(unsigned long addr)
> -{
> -       /* Overflowing the slots list should be impossible. */
> -       if (slot_max >= CONFIG_RANDOMIZE_BASE_MAX_OFFSET /
> -                       CONFIG_PHYSICAL_ALIGN)
> -               return;
> -
> -       slots[slot_max++] = addr;
> -}
> -
>  static unsigned long slots_fetch_random(void)
>  {
> +       unsigned long random;
> +       int i;
> +
>         /* Handle case of no slots stored. */
>         if (slot_max == 0)
>                 return 0;
>
> -       return slots[get_random_long() % slot_max];
> +       random = get_random_long() % slot_max;
> +
> +       for (i=0; i< slot_area_index; i++) {
> +               if (random > slot_areas[i].num) {
> +                       random -= slot_areas[i].num;
> +                       continue;
> +               }
> +               return slot_areas[i].addr + random * CONFIG_PHYSICAL_ALIGN;
> +       }
> +
> +       if (i == slot_area_index )
> +               debug_putstr("something wrong happened in slots_fetch_random()...\n");
> +       return 0;
>  }
>
>  static int process_e820_entry(struct e820entry *entry,
> @@ -362,7 +364,7 @@ repeat:
>         goto repeat;
>  }
>
> -static unsigned long find_random_addr(unsigned long minimum,
> +static unsigned long find_random_phy_addr(unsigned long minimum,
>                                       unsigned long size)
>  {
>         int i;
> @@ -374,6 +376,8 @@ static unsigned long find_random_addr(unsigned long minimum,
>         /* Verify potential e820 positions, appending to slots list. */
>         for (i = 0; i < real_mode->e820_entries; i++) {
>                 process_e820_entry(&real_mode->e820_map[i], minimum, size);
> +               if ( slot_area_index == MAX_SLOT_AREA )
> +                       break;

I wonder if this should emit a printk warning?

-Kees

>         }
>
>         return slots_fetch_random();
> --
> 1.9.3
>



-- 
Kees Cook
Chrome OS Security
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