Re: [PATCH v3 2/2] x86/boot/KASLR: Restrict kernel to be randomized in mirror regions

[Baoquan He]

On 07/05/17 at 03:08pm, Kees Cook wrote:
> On Wed, Jul 5, 2017 at 1:06 AM, Baoquan He <bhe@xxxxxxxxxx> wrote:
> > Kernel text may be located in non-mirror regions (movable zone) when both
> > address range mirroring feature and KASLR are enabled.
> >
> > The address range mirroring feature arranges such mirror region into
> > normal zone and other region into movable zone in order to locate
> > kernel code and data in mirror region. The physical memory region
> > whose descriptors in EFI memory map has EFI_MEMORY_MORE_RELIABLE
> > attribute (bit: 16) are mirrored.
> >
> > If efi is detected, iterate efi memory map and pick the mirror region to
> > process for adding candidate of randomization slot. If efi is disabled
> > or no mirror region found, still process e820 memory map.
> >
> > Signed-off-by: Baoquan He <bhe@xxxxxxxxxx>
> > ---
> >  arch/x86/boot/compressed/kaslr.c | 52 +++++++++++++++++++++++++++++++++++++++-
> >  1 file changed, 51 insertions(+), 1 deletion(-)
> >
> > diff --git a/arch/x86/boot/compressed/kaslr.c b/arch/x86/boot/compressed/kaslr.c
> > index 85c360eec4a6..94f08fd375ae 100644
> > --- a/arch/x86/boot/compressed/kaslr.c
> > +++ b/arch/x86/boot/compressed/kaslr.c
> > @@ -37,7 +37,9 @@
> >  #include <linux/uts.h>
> >  #include <linux/utsname.h>
> >  #include <linux/ctype.h>
> > +#include <linux/efi.h>
> >  #include <generated/utsrelease.h>
> > +#include <asm/efi.h>
> >
> >  /* Macros used by the included decompressor code below. */
> >  #define STATIC
> > @@ -558,6 +560,48 @@ static void process_mem_region(struct mem_vector *entry,
> >         }
> >  }
> >
> > +/* Marks if efi mirror regions have been found and handled. */
> > +static bool efi_mirror_found;
> > +
> > +static void process_efi_entry(unsigned long minimum, unsigned long image_size)
> 
> Since this walks all entries (not a single entry), please name it
> process_efi_entries() (or some other more clear name).

Thanks for your reviewing, Kees!

Ok, will change. Since the e820 function was named as
process_e820_entry, I just did similarly. It makes sense to change as
you suggested, and the process_e820_entry too as you commented in v2
thread.

Thanks
Baoquan

> > +{
> > +       struct efi_info *e = &boot_params->efi_info;
> > +       struct mem_vector region;
> > +       efi_memory_desc_t *md;
> > +       unsigned long pmap;
> > +       char *signature;
> > +       u32 nr_desc;
> > +       int i;
> > +
> > +
> > +       signature = (char *)&boot_params->efi_info.efi_loader_signature;
> > +       if (strncmp(signature, EFI32_LOADER_SIGNATURE, 4) &&
> > +           strncmp(signature, EFI64_LOADER_SIGNATURE, 4))
> > +               return;
> > +
> > +#ifdef CONFIG_X86_32
> > +       /* Can't handle data above 4GB at this time */
> > +       if (e->efi_memmap_hi) {
> > +               warn("Memory map is above 4GB, EFI should be disabled.\n");
> > +               return;
> > +       }
> > +       pmap =  e->efi_memmap;
> > +#else
> > +       pmap = (e->efi_memmap | ((__u64)e->efi_memmap_hi << 32));
> > +#endif
> > +
> > +       nr_desc = e->efi_memmap_size / e->efi_memdesc_size;
> > +       for (i = 0; i < nr_desc; i++) {
> > +               md = (efi_memory_desc_t *)(pmap + (i * e->efi_memdesc_size));
> > +               if (md->attribute & EFI_MEMORY_MORE_RELIABLE) {
> > +                       region.start = md->phys_addr;
> > +                       region.size = md->num_pages << EFI_PAGE_SHIFT;
> > +                       process_mem_region(&region, minimum, image_size);
> > +                       efi_mirror_found = true;
> > +               }
> > +       }
> > +}
> > +
> >  static void process_e820_entry(unsigned long minimum, unsigned long image_size)
> >  {
> >         int i;
> > @@ -592,6 +636,12 @@ static unsigned long find_random_phys_addr(unsigned long minimum,
> >         /* Make sure minimum is aligned. */
> >         minimum = ALIGN(minimum, CONFIG_PHYSICAL_ALIGN);
> >
> > +#ifdef CONFIG_EFI
> > +       process_efi_entry(minimum, image_size);
> > +       if (efi_mirror_found)
> > +               return slots_fetch_random();
> > +#endif
> > +
> >         process_e820_entry(minimum, image_size);
> >         return slots_fetch_random();
> >  }
> > @@ -651,7 +701,7 @@ void choose_random_location(unsigned long input,
> >          */
> >         min_addr = min(*output, 512UL << 20);
> >
> > -       /* Walk e820 and find a random address. */
> > +       /* Walk available memory entries to find a random address. */
> >         random_addr = find_random_phys_addr(min_addr, output_size);
> >         if (!random_addr) {
> >                 warn("Physical KASLR disabled: no suitable memory region!");
> > --
> > 2.5.5
> >
> 
> 
> 
> -- 
> Kees Cook
> Pixel Security