Re: [PATCH v2 1/2] x86/boot/KASLR: Adapt process_e820_entry for any type of memory entry

[Kees Cook]

On Tue, Jul 4, 2017 at 1:04 AM, Baoquan He <bhe@xxxxxxxxxx> wrote:
> Now function process_e820_entry is only used to process e820 memory
> entries. Adapt it for any type of memory entry, not just for e820.
> Later we will use it to process efi mirror regions.
>
> So rename the old process_e820_entry to process_mem_region, and
> extract and wrap the e820 specific processing code into process_e820_entry.

This mixes changing the structure internals (.addr vs .start) with
changing the processing logic (adding a wrapper). I would prefer this
was done in several stages to make review easier:

1) lift e820 walking into a new function process_e820_entries(), and
move TYPE_RAM logic there.

2) switch process_e820_entry() from struct boot_e820_entry to struct mem_vector.

3) rename (and adjust comments!) of process_e820_entry() into
process_mem_region().

-Kees

>
> Signed-off-by: Baoquan He <bhe@xxxxxxxxxx>
> ---
>  arch/x86/boot/compressed/kaslr.c | 60 ++++++++++++++++++++++------------------
>  1 file changed, 33 insertions(+), 27 deletions(-)
>
> diff --git a/arch/x86/boot/compressed/kaslr.c b/arch/x86/boot/compressed/kaslr.c
> index 91f27ab970ef..85c360eec4a6 100644
> --- a/arch/x86/boot/compressed/kaslr.c
> +++ b/arch/x86/boot/compressed/kaslr.c
> @@ -479,35 +479,31 @@ static unsigned long slots_fetch_random(void)
>         return 0;
>  }
>
> -static void process_e820_entry(struct boot_e820_entry *entry,
> +static void process_mem_region(struct mem_vector *entry,
>                                unsigned long minimum,
>                                unsigned long image_size)
>  {
>         struct mem_vector region, overlap;
>         struct slot_area slot_area;
>         unsigned long start_orig, end;
> -       struct boot_e820_entry cur_entry;
> -
> -       /* Skip non-RAM entries. */
> -       if (entry->type != E820_TYPE_RAM)
> -               return;
> +       struct mem_vector cur_entry;
>
>         /* On 32-bit, ignore entries entirely above our maximum. */
> -       if (IS_ENABLED(CONFIG_X86_32) && entry->addr >= KERNEL_IMAGE_SIZE)
> +       if (IS_ENABLED(CONFIG_X86_32) && entry->start >= KERNEL_IMAGE_SIZE)
>                 return;
>
>         /* Ignore entries entirely below our minimum. */
> -       if (entry->addr + entry->size < minimum)
> +       if (entry->start + entry->size < minimum)
>                 return;
>
>         /* Ignore entries above memory limit */
> -       end = min(entry->size + entry->addr, mem_limit);
> -       if (entry->addr >= end)
> +       end = min(entry->size + entry->start, mem_limit);
> +       if (entry->start >= end)
>                 return;
> -       cur_entry.addr = entry->addr;
> -       cur_entry.size = end - entry->addr;
> +       cur_entry.start = entry->start;
> +       cur_entry.size = end - entry->start;
>
> -       region.start = cur_entry.addr;
> +       region.start = cur_entry.start;
>         region.size = cur_entry.size;
>
>         /* Give up if slot area array is full. */
> @@ -522,7 +518,7 @@ static void process_e820_entry(struct boot_e820_entry *entry,
>                 region.start = ALIGN(region.start, CONFIG_PHYSICAL_ALIGN);
>
>                 /* Did we raise the address above this e820 region? */
> -               if (region.start > cur_entry.addr + cur_entry.size)
> +               if (region.start > cur_entry.start + cur_entry.size)
>                         return;
>
>                 /* Reduce size by any delta from the original address. */
> @@ -562,12 +558,31 @@ static void process_e820_entry(struct boot_e820_entry *entry,
>         }
>  }
>
> -static unsigned long find_random_phys_addr(unsigned long minimum,
> -                                          unsigned long image_size)
> +static void process_e820_entry(unsigned long minimum, unsigned long image_size)
>  {
>         int i;
> -       unsigned long addr;
> +       struct mem_vector region;
> +       struct boot_e820_entry *entry;
> +
> +       /* Verify potential e820 positions, appending to slots list. */
> +       for (i = 0; i < boot_params->e820_entries; i++) {
> +               entry = &boot_params->e820_table[i];
> +               /* Skip non-RAM entries. */
> +               if (entry->type != E820_TYPE_RAM)
> +                       continue;
> +               region.start = entry->addr;
> +               region.size = entry->size;
> +               process_mem_region(&region, minimum, image_size);
> +               if (slot_area_index == MAX_SLOT_AREA) {
> +                       debug_putstr("Aborted e820 scan (slot_areas full)!\n");
> +                       break;
> +               }
> +       }
> +}
>
> +static unsigned long find_random_phys_addr(unsigned long minimum,
> +                                          unsigned long image_size)
> +{
>         /* Check if we had too many memmaps. */
>         if (memmap_too_large) {
>                 debug_putstr("Aborted e820 scan (more than 4 memmap= args)!\n");
> @@ -577,16 +592,7 @@ static unsigned long find_random_phys_addr(unsigned long minimum,
>         /* Make sure minimum is aligned. */
>         minimum = ALIGN(minimum, CONFIG_PHYSICAL_ALIGN);
>
> -       /* Verify potential e820 positions, appending to slots list. */
> -       for (i = 0; i < boot_params->e820_entries; i++) {
> -               process_e820_entry(&boot_params->e820_table[i], minimum,
> -                                  image_size);
> -               if (slot_area_index == MAX_SLOT_AREA) {
> -                       debug_putstr("Aborted e820 scan (slot_areas full)!\n");
> -                       break;
> -               }
> -       }
> -
> +       process_e820_entry(minimum, image_size);
>         return slots_fetch_random();
>  }
>
> --
> 2.5.5
>



-- 
Kees Cook
Pixel Security