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

Tom Lendacky
2017-08-17T18:42:04Z

On 7/28/2017 5:31 AM, Borislav Petkov wrote:
> On Mon, Jul 24, 2017 at 02:07:48PM -0500, Brijesh Singh wrote:
>> From: Tom Lendacky <thomas.lendacky@amd.com>
>>
>> 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@amd.com>
>> Signed-off-by: Brijesh Singh <brijesh.singh@amd.com>
>> ---
>> 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...

Will do.

>
>> +
>> /* 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.

Yup.

Thanks,
Tom

>
>> +
>> efi_update_mappings(md, pf);
>
> In general, I'm not totally excited about that sprinkling of if
> (sev_active())... :-\
>