Messages in this thread | | | From | Sai Praneeth Prakhya <> | Subject | [PATCH V2 0/2] Unmap EFI boot services code/data regions after boot. | Date | Fri, 26 Oct 2018 14:38:43 -0700 |
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CC'ing x86 folks because this patch touches x86/mm which I am no expert of.
[Copied from Patch 1] 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() [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 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 (2): 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 | 2 ++ arch/x86/mm/pageattr.c | 26 ++++++++++++++++++++++++++ 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, 57 insertions(+), 7 deletions(-)
Signed-off-by: Sai Praneeth Prakhya <sai.praneeth.prakhya@intel.com> Cc: Borislav Petkov <bp@alien8.de> Cc: Ingo Molnar <mingo@kernel.org> Cc: Andy Lutomirski <luto@kernel.org> Cc: Dave Hansen <dave.hansen@intel.com> Cc: Bhupesh Sharma <bhsharma@redhat.com> Cc: Thomas Gleixner <tglx@linutronix.de> Cc: Peter Zijlstra <peterz@infradead.org> Cc: Ard Biesheuvel <ard.biesheuvel@linaro.org>
-- 2.19.1
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