Re: [RFC Part1 PATCH v3 08/17] x86/efi: Access EFI data as encrypted when SEV is active

Borislav Petkov
2017-07-28T10:31:52Z

On Mon, Jul 24, 2017 at 02:07:48PM -0500, Brijesh Singh wrote:
> From: Tom Lendacky <thomas.lendacky-5C7GfCeVMHo@public.gmane.org>
>
> EFI data is encrypted when the kernel is run under SEV. Update the
> page table references to be sure the EFI memory areas are accessed
> encrypted.
>
> Signed-off-by: Tom Lendacky <thomas.lendacky-5C7GfCeVMHo@public.gmane.org>
> Signed-off-by: Brijesh Singh <brijesh.singh-5C7GfCeVMHo@public.gmane.org>
> ---
> arch/x86/platform/efi/efi_64.c | 15 ++++++++++++++-
> 1 file changed, 14 insertions(+), 1 deletion(-)
>
> diff --git a/arch/x86/platform/efi/efi_64.c b/arch/x86/platform/efi/efi_64.c
> index 12e8388..1ecb3f6 100644
> --- a/arch/x86/platform/efi/efi_64.c
> +++ b/arch/x86/platform/efi/efi_64.c
> @@ -32,6 +32,7 @@
> #include <linux/reboot.h>
> #include <linux/slab.h>
> #include <linux/ucs2_string.h>
> +#include <linux/mem_encrypt.h>
>
> #include <asm/setup.h>
> #include <asm/page.h>
> @@ -369,7 +370,10 @@ int __init efi_setup_page_tables(unsigned long pa_memmap, unsigned num_pages)
> * as trim_bios_range() will reserve the first page and isolate it away
> * from memory allocators anyway.
> */
> - if (kernel_map_pages_in_pgd(pgd, 0x0, 0x0, 1, _PAGE_RW)) {
> + pf = _PAGE_RW;
> + if (sev_active())
> + pf |= _PAGE_ENC;

\n here

> + if (kernel_map_pages_in_pgd(pgd, 0x0, 0x0, 1, pf)) {
> pr_err("Failed to create 1:1 mapping for the first page!\n");
> return 1;
> }
> @@ -412,6 +416,9 @@ static void __init __map_region(efi_memory_desc_t *md, u64 va)
> if (!(md->attribute & EFI_MEMORY_WB))
> flags |= _PAGE_PCD;
>
> + if (sev_active())
> + flags |= _PAGE_ENC;
> +
> pfn = md->phys_addr >> PAGE_SHIFT;
> if (kernel_map_pages_in_pgd(pgd, pfn, va, md->num_pages, flags))
> pr_warn("Error mapping PA 0x%llx -> VA 0x%llx!\n",
> @@ -511,6 +518,9 @@ static int __init efi_update_mappings(efi_memory_desc_t *md, unsigned long pf)
> pgd_t *pgd = efi_pgd;
> int err1, err2;
>
> + if (sev_active())
> + pf |= _PAGE_ENC;

Move this assignment to the caller efi_update_mem_attr() where pf is being
set...

> +
> /* Update the 1:1 mapping */
> pfn = md->phys_addr >> PAGE_SHIFT;
> err1 = kernel_map_pages_in_pgd(pgd, pfn, md->phys_addr, md->num_pages, pf);
> @@ -589,6 +599,9 @@ void __init efi_runtime_update_mappings(void)
> (md->type != EFI_RUNTIME_SERVICES_CODE))
> pf |= _PAGE_RW;
>
> + if (sev_active())
> + pf |= _PAGE_ENC;

... just like here.

> +
> efi_update_mappings(md, pf);

In general, I'm not totally excited about that sprinkling of if
(sev_active())... :-\

--
Regards/Gruss,
Boris.

SUSE Linux GmbH, GF: Felix Imendörffer, Jane Smithard, Graham Norton, HRB 21284 (AG Nürnberg)
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