Re: [PATCH v9 2/2] x86/boot/KASLR: Restrict kernel to be randomized in mirror regions

[Baoquan He]

On 08/18/17 at 04:10pm, Ard Biesheuvel wrote:
> On 17 August 2017 at 14:04, Baoquan He <bhe@xxxxxxxxxx> wrote:

> > Thanks a lot for helping improving the patch log, Ingo! Will pay more
> > attention to the description in words and paragraph partition of log.
> >
> >>
> >> So 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>
> 
> 
> Could the x86 people on cc either take these directly, or indicate
> whether they are ok with this going in via the EFI tree?

Thanks for looking into this, Ard. I saw Ingo has put these into
tip/x86/boot.

> 
> >> ---
> >>  arch/x86/boot/compressed/kaslr.c | 68 ++++++++++++++++++++++++++++++++++++++--
> >>  1 file changed, 66 insertions(+), 2 deletions(-)
> >>
> >> diff --git a/arch/x86/boot/compressed/kaslr.c b/arch/x86/boot/compressed/kaslr.c
> >> index 99c7194f7ea6..7de23bb279ce 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 +560,65 @@ static void process_mem_region(struct mem_vector *entry,
> >>       }
> >>  }
> >>
> >> +#ifdef CONFIG_EFI
> >> +/*
> >> + * Returns true if mirror region found (and must have been processed
> >> + * for slots adding)
> >> + */
> >> +static bool
> >> +process_efi_entries(unsigned long minimum, unsigned long image_size)
> >> +{
> >> +     struct efi_info *e = &boot_params->efi_info;
> >> +     bool efi_mirror_found = false;
> >> +     struct mem_vector region;
> >> +     efi_memory_desc_t *md;
> >> +     unsigned long pmap;
> >> +     char *signature;
> >> +     u32 nr_desc;
> >> +     int i;
> >> +
> >> +     signature = (char *)&e->efi_loader_signature;
> >> +     if (strncmp(signature, EFI32_LOADER_SIGNATURE, 4) &&
> >> +         strncmp(signature, EFI64_LOADER_SIGNATURE, 4))
> >> +             return false;
> >> +
> >> +#ifdef CONFIG_X86_32
> >> +     /* Can't handle data above 4GB at this time */
> >> +     if (e->efi_memmap_hi) {
> >> +             warn("EFI memmap is above 4GB, can't be handled now on x86_32. EFI should be disabled.\n");
> >> +             return false;
> >> +     }
> >> +     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_early_memdesc_ptr(pmap, e->efi_memdesc_size, i);
> >> +             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;
> >> +
> >> +                     if (slot_area_index == MAX_SLOT_AREA) {
> >> +                             debug_putstr("Aborted EFI scan (slot_areas full)!\n");
> >> +                             break;
> >> +                     }
> >> +             }
> >> +     }
> >> +
> >> +     return efi_mirror_found;
> >> +}
> >> +#else
> >> +static inline bool
> >> +process_efi_entries(unsigned long minimum, unsigned long image_size)
> >> +{
> >> +     return false;
> >> +}
> >> +#endif
> >> +
> >>  static void process_e820_entries(unsigned long minimum,
> >>                                unsigned long image_size)
> >>  {
> >> @@ -586,13 +647,16 @@ static unsigned long find_random_phys_addr(unsigned long minimum,
> >>  {
> >>       /* Check if we had too many memmaps. */
> >>       if (memmap_too_large) {
> >> -             debug_putstr("Aborted e820 scan (more than 4 memmap= args)!\n");
> >> +             debug_putstr("Aborted memory entries scan (more than 4 memmap= args)!\n");
> >>               return 0;
> >>       }
> >>
> >>       /* Make sure minimum is aligned. */
> >>       minimum = ALIGN(minimum, CONFIG_PHYSICAL_ALIGN);
> >>
> >> +     if (process_efi_entries(minimum, image_size))
> >> +             return slots_fetch_random();
> >> +
> >>       process_e820_entries(minimum, image_size);
> >>       return slots_fetch_random();
> >>  }
> >> @@ -652,7 +716,7 @@ 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
> >>