CC'ing x86 folks because this patch set touches x86/mm which I am no expert of. Ideally, after kernel assumes control of the platform, firmware shouldn't access EFI boot services code/data regions. But, it's noticed that this is not so true in many x86 platforms. Hence, during boot, kernel reserves EFI boot services code/data regions [1] and maps [2] them to efi_pgd so that call to set_virtual_address_map() doesn't fail. After returning from set_virtual_address_map(), kernel frees the reserved regions [3] but they still remain mapped. This means that any code that's running in efi_pgd address space (e.g: any EFI runtime service) would still be able to access EFI boot services code/data regions but the contents of these regions would have long been over written by someone else as they are freed by efi_free_boot_services(). So, it's important to unmap these regions. After unmapping EFI boot services code/data regions, any illegal access by buggy firmware to these regions would result in page fault which will be handled by efi specific fault handler. Unmapping EFI boot services code/data regions will result in clearing PAGE_PRESENT bit and it shouldn't bother L1TF cases because it's already handled by protnone_mask() at arch/x86/include/asm/pgtable-invert.h. [1] Please see efi_reserve_boot_services() [2] Please see efi_map_region() -> __map_region() -> kernel_map_pages_in_pgd() [3] Please see efi_free_boot_services() Testing the patch set: ---------------------- 1. Download buggy firmware (which accesses boot regions even after kernel has booted) from here [1]. 2. Without the patch set, you shouldn't see any kernel warning/error messages (i.e. kernel allows accesses to EFI boot services code/data regions even after call to set_virtual_address_map()). 3. With the patch set, you should see a kernel warning about buggy firmware, efi_rts_wq beeing freezed and disabling runtime services forever. Please note that this patch will change kernel's existing behavior for some EFI runtime services but I think it's OK because kernel should have never allowed those accesses in the first place. Also please note that this patch set needs lot of real time trashing as I just tested it out with OVMF. Note: ----- Patch set based on "next" branch in efi tree. Changes from V2 -> V3: ---------------------- 1. Expliclty set pfn to 0 in kernel_unmap_pages_in_pgd(). 2. Add __init modifier to kernel_<map/unmap>_pages_in_pgd(). 3. Warn if kernel_<map/unmap>_pages_in_pgd() are called after smp_init(). 4. Split efi_unmap_pages() into a separate patch. Changes from V1 -> V2: ---------------------- 1. Rewrite the cpa initializer in a more readable fashion. 2. Don't use cpa->pfn while unmapping, as it's not useful. 3. Unmap regions before freeing them up. 4. Fix spelling nits. Sai Praneeth (3): x86/mm/pageattr: Introduce helper function to unmap EFI boot services x86/efi: Unmap EFI boot services code/data regions from efi_pgd x86/efi: Move efi_<reserve/free>_boot_services() to arch/x86 arch/x86/include/asm/efi.h | 2 ++ arch/x86/include/asm/pgtable_types.h | 8 ++++++-- arch/x86/mm/pageattr.c | 40 ++++++++++++++++++++++++++++++++++-- arch/x86/platform/efi/efi.c | 2 ++ arch/x86/platform/efi/quirks.c | 25 ++++++++++++++++++++++ include/linux/efi.h | 3 --- init/main.c | 4 ---- 7 files changed, 73 insertions(+), 11 deletions(-) Signed-off-by: Sai Praneeth Prakhya <sai.praneeth.prakhya@xxxxxxxxx> Cc: Borislav Petkov <bp@xxxxxxxxx> Cc: Ingo Molnar <mingo@xxxxxxxxxx> Cc: Andy Lutomirski <luto@xxxxxxxxxx> Cc: Dave Hansen <dave.hansen@xxxxxxxxx> Cc: Bhupesh Sharma <bhsharma@xxxxxxxxxx> Cc: Thomas Gleixner <tglx@xxxxxxxxxxxxx> Cc: Peter Zijlstra <peterz@xxxxxxxxxxxxx> Cc: Ard Biesheuvel <ard.biesheuvel@xxxxxxxxxx> -- 2.7.4
