On 6/3/2024 3:56 AM, Borislav Petkov wrote
EFI memory map and due to early allocation it uses memblock allocation.
Later during boot, efi_enter_virtual_mode() calls kexec_enter_virtual_mode()
in case of a kexec-ed kernel boot.
This function kexec_enter_virtual_mode() installs the new EFI memory map by
calling efi_memmap_init_late() which remaps the efi_memmap physically allocated
in efi_arch_mem_reserve(), but this remapping is still using memblock allocation.
Subsequently, when memblock is freed later in boot flow, this remapped
efi_memmap will have random corruption (similar to a use-after-free scenario).
The corrupted EFI memory map is then passed to the next kexec-ed kernel
which causes a panic when trying to use the corrupted EFI memory map.
This sounds fishy: memblock allocated memory is not freed later in the
boot - it remains reserved. Only free memory is freed from memblock to
the buddy allocator.
Or is the problem that memblock-allocated memory cannot be memremapped
because *raisins*?
This is what seems to be happening:
efi_arch_mem_reserve() calls efi_memmap_alloc() to allocate memory for
EFI memory map and due to early allocation it uses memblock allocation.
And later efi_enter_virtual_mode() calls kexec_enter_virtual_mode()
in case of a kexec-ed kernel boot.
This function kexec_enter_virtual_mode() installs the new EFI memory map by
calling efi_memmap_init_late() which does memremap() on memblock-allocated memory.
Thanks, Ashish
Mike?
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