在 2022/5/3 17:58, Ard Biesheuvel 写道:
On Tue, 19 Apr 2022 at 08:43, Wupeng Ma <mawupeng1@xxxxxxxxxx> wrote:
From: Ma Wupeng <mawupeng1@xxxxxxxxxx>
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;
.
