On 22/09/2016 16:35, Borislav Petkov wrote: >> > @@ -230,6 +230,10 @@ int __init efi_setup_page_tables(unsigned long pa_memmap, unsigned num_pages) >> > efi_scratch.efi_pgt = (pgd_t *)__sme_pa(efi_pgd); >> > pgd = efi_pgd; >> > >> > + flags = _PAGE_NX | _PAGE_RW; >> > + if (sev_active) >> > + flags |= _PAGE_ENC; > So this is confusing me. There's this patch which says EFI data is > accessed in the clear: > > https://lkml.kernel.org/r/20160822223738.29880.6909.stgit@xxxxxxxxxxxxxxxxxxxxxxxxx > > but now here it is encrypted when SEV is enabled. > > Do you mean, it is encrypted here because we're in the guest kernel? I suspect this patch is untested, and also wrong. :) The main difference between the SME and SEV encryption, from the point of view of the kernel, is that real-mode always writes unencrypted in SME and always writes encrypted in SEV. But UEFI can run in 64-bit mode and learn about the C bit, so EFI boot data should be unprotected in SEV guests. Because the firmware volume is written to high memory in encrypted form, and because the PEI phase runs in 32-bit mode, the firmware code will be encrypted; on the other hand, data that is placed in low memory for the kernel can be unencrypted, thus limiting differences between SME and SEV. Important: I don't know what you guys are doing for SEV and Windows guests, but if you are doing something I would really appreciate doing things in the open. If Linux and Windows end up doing different things with EFI boot data, ACPI tables, etc. it will be a huge pain. On the other hand, if we can enjoy being first, that's great. In fact, I have suggested in the QEMU list that SEV guests should always use UEFI; because BIOS runs in real-mode or 32-bit non-paging protected mode, BIOS must always write encrypted data, which becomes painful in the kernel. And regarding the above "important" point, all I know is that Microsoft for sure will be happy to restrict SEV to UEFI guests. :) There are still some differences, mostly around the real mode trampoline executed by the kernel, but they should be much smaller. Paolo -- To unsubscribe from this list: send the line "unsubscribe linux-efi" in the body of a message to majordomo@xxxxxxxxxxxxxxx More majordomo info at http://vger.kernel.org/majordomo-info.html
