lkml.org 
[lkml]   [2022]   [May]   [7]   [last100]   RSS Feed
Views: [wrap][no wrap]   [headers]  [forward] 
 
Messages in this thread
/
Date
SubjectRe: [PATCH 0/2] Add support to relocate kernel image to mirrored region
From


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;
> .

\
 
 \ /
  Last update: 2022-05-07 11:30    [W:2.313 / U:0.008 seconds]
©2003-2020 Jasper Spaans|hosted at Digital Ocean and TransIP|Read the blog|Advertise on this site