Re: [PATCH 0/2] Add support to relocate kernel image to mirrored region

[mawupeng <mawupeng1@huawei.com>]

在 2022/5/3 17:58, Ard Biesheuvel 写道:
> On Tue, 19 Apr 2022 at 08:43, Wupeng Ma <mawupeng1@huawei.com> wrote:
>>
>> From: Ma Wupeng <mawupeng1@huawei.com>
>>
>> Now system image will perfer to be located to mirrored regions both KASLR
>> on and off.
>>
> 
> Hello Ma Wupeng,
> 
> I wonder if we could simplify this as follows:
> - ignore the non-KASLR case for now, and rely on the bootloader  > load the image into mirrored memory if it exists;

In grub, memory for static image is allocated via the following path:

grub_cmd_linux
   kernel = grub_malloc(filelen)
   kernel_alloc_addr = grub_efi_allocate_any_pages (kernel_alloc_pages)
   grub_memcpy (kernel_addr, kernel, grub_min(filelen, kernel_size))
    grub_loader_set (grub_linux_boot, grub_linux_unload, 0)

Can we get memory from mirrored region by the following steps:
1. get memory map by calling grub_efi_get_memory_map()
2. iter all memory map to find a suitable mirrored memory area
3. locate kernel image to this area

So, if kaslr is not enabled
  - grub will load kernel into mirrored region
else
  - arm64-stub.c will relocate kernel image to mirrored region

Is this feasible?

> - simplify the KASLR case to the below.

Yes, we can certainly do this. I will remove my code and use yours.

> 
> I think this is reasonable, because it means we take mirrored memory
> into account when we decide to move the image anyway, but expect the
> boot chain to take care of this if there is no need to move the image.
> 
> -------------8<------------------
> --- a/drivers/firmware/efi/libstub/randomalloc.c
> +++ b/drivers/firmware/efi/libstub/randomalloc.c
> @@ -56,6 +56,7 @@ efi_status_t efi_random_alloc(unsigned long size,
>                                unsigned long random_seed)
>   {
>          unsigned long map_size, desc_size, total_slots = 0, target_slot;
> +       unsigned long total_mirrored_slots = 0;
>          unsigned long buff_size;
>          efi_status_t status;
>          efi_memory_desc_t *memory_map;
> @@ -86,8 +87,14 @@ efi_status_t efi_random_alloc(unsigned long size,
>                  slots = get_entry_num_slots(md, size, ilog2(align));
>                  MD_NUM_SLOTS(md) = slots;
>                  total_slots += slots;
> +               if (md->attribute & EFI_MEMORY_MORE_RELIABLE)
> +                       total_mirrored_slots += slots;
>          }
> 
> +       /* only consider mirrored slots for randomization if any exist */
> +       if (total_mirrored_slots > 0)
> +               total_slots = total_mirrored_slots;
> +
>          /* find a random number between 0 and total_slots */
>          target_slot = (total_slots * (u64)(random_seed & U32_MAX)) >> 32;
> 
> @@ -107,6 +114,10 @@ efi_status_t efi_random_alloc(unsigned long size,
>                  efi_physical_addr_t target;
>                  unsigned long pages;
> 
> +               if (total_mirrored_slots > 0 &&
> +                   !(md->attribute & EFI_MEMORY_MORE_RELIABLE))
> +                       continue;
> +
>                  if (target_slot >= MD_NUM_SLOTS(md)) {
>                          target_slot -= MD_NUM_SLOTS(md);
>                          continue;
> .