linux-kernel - Re: [RFC PATCH v1 09/28] x86/efi: Access EFI data as encrypted when SEV is active

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Date:   Thu, 22 Sep 2016 16:35:45 +0200
From:   Borislav Petkov <bp@...e.de>
To:     Brijesh Singh <brijesh.singh@....com>, thomas.lendacky@....com
Cc:     simon.guinot@...uanux.org, linux-efi@...r.kernel.org,
        kvm@...r.kernel.org, rkrcmar@...hat.com, matt@...eblueprint.co.uk,
        linus.walleij@...aro.org, linux-mm@...ck.org,
        paul.gortmaker@...driver.com, hpa@...or.com,
        dan.j.williams@...el.com, aarcange@...hat.com,
        sfr@...b.auug.org.au, andriy.shevchenko@...ux.intel.com,
        herbert@...dor.apana.org.au, bhe@...hat.com, xemul@...allels.com,
        joro@...tes.org, x86@...nel.org, mingo@...hat.com,
        msalter@...hat.com, ross.zwisler@...ux.intel.com,
        dyoung@...hat.com, thomas.lendacky@....com, jroedel@...e.de,
        keescook@...omium.org, toshi.kani@....com,
        mathieu.desnoyers@...icios.com, devel@...uxdriverproject.org,
        tglx@...utronix.de, mchehab@...nel.org, iamjoonsoo.kim@....com,
        labbott@...oraproject.org, tony.luck@...el.com,
        alexandre.bounine@....com, kuleshovmail@...il.com,
        linux-kernel@...r.kernel.org, mcgrof@...nel.org,
        linux-crypto@...r.kernel.org, pbonzini@...hat.com,
        akpm@...ux-foundation.org, davem@...emloft.net
Subject: Re: [RFC PATCH v1 09/28] x86/efi: Access EFI data as encrypted when
 SEV is active

On Mon, Aug 22, 2016 at 07:25:25PM -0400, Brijesh Singh wrote:
> From: Tom Lendacky <thomas.lendacky@....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@....com>
> ---
>  arch/x86/platform/efi/efi_64.c |   14 ++++++++++++--
>  1 file changed, 12 insertions(+), 2 deletions(-)
> 
> diff --git a/arch/x86/platform/efi/efi_64.c b/arch/x86/platform/efi/efi_64.c
> index 0871ea4..98363f3 100644
> --- a/arch/x86/platform/efi/efi_64.c
> +++ b/arch/x86/platform/efi/efi_64.c
> @@ -213,7 +213,7 @@ void efi_sync_low_kernel_mappings(void)
>  
>  int __init efi_setup_page_tables(unsigned long pa_memmap, unsigned num_pages)
>  {
> -	unsigned long pfn, text;
> +	unsigned long pfn, text, flags;
>  	efi_memory_desc_t *md;
>  	struct page *page;
>  	unsigned npages;
> @@ -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@tlendack-t1.amdoffice.net

but now here it is encrypted when SEV is enabled.

Do you mean, it is encrypted here because we're in the guest kernel?

Thanks.

-- 
Regards/Gruss,
    Boris.

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