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

[Tom Lendacky]

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@xxxxxxx>
> >
> > 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@xxxxxxx>
> > Signed-off-by: Brijesh Singh <brijesh.singh@xxxxxxx>
> > ---
> >   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())... :-\