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

[Baoquan He]

On 07/05/17 at 03:06pm, Kees Cook wrote:
> 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:

OK, will do following below steps. Thanks!

> 
> 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