linux-kernel - Re: [RFC Part1 PATCH v3 06/17] x86/mm: Use encrypted access of boot related data with SEV

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Message-ID: <20170727133125.GB28553@nazgul.tnic>
Date:   Thu, 27 Jul 2017 15:31:25 +0200
From:   Borislav Petkov <bp@...e.de>
To:     Brijesh Singh <brijesh.singh@....com>
Cc:     linux-kernel@...r.kernel.org, x86@...nel.org,
        linux-efi@...r.kernel.org, linuxppc-dev@...ts.ozlabs.org,
        kvm@...r.kernel.org, Thomas Gleixner <tglx@...utronix.de>,
        Ingo Molnar <mingo@...hat.com>,
        "H . Peter Anvin" <hpa@...or.com>,
        Andy Lutomirski <luto@...nel.org>,
        Tony Luck <tony.luck@...el.com>,
        Piotr Luc <piotr.luc@...el.com>,
        Tom Lendacky <thomas.lendacky@....com>,
        Fenghua Yu <fenghua.yu@...el.com>,
        Lu Baolu <baolu.lu@...ux.intel.com>,
        Reza Arbab <arbab@...ux.vnet.ibm.com>,
        David Howells <dhowells@...hat.com>,
        Matt Fleming <matt@...eblueprint.co.uk>,
        "Kirill A . Shutemov" <kirill.shutemov@...ux.intel.com>,
        Laura Abbott <labbott@...hat.com>,
        Ard Biesheuvel <ard.biesheuvel@...aro.org>,
        Andrew Morton <akpm@...ux-foundation.org>,
        Eric Biederman <ebiederm@...ssion.com>,
        Benjamin Herrenschmidt <benh@...nel.crashing.org>,
        Paul Mackerras <paulus@...ba.org>,
        Konrad Rzeszutek Wilk <konrad.wilk@...cle.com>,
        Jonathan Corbet <corbet@....net>,
        Dave Airlie <airlied@...hat.com>,
        Kees Cook <keescook@...omium.org>,
        Paolo Bonzini <pbonzini@...hat.com>,
        Radim Krčmář <rkrcmar@...hat.com>,
        Arnd Bergmann <arnd@...db.de>, Tejun Heo <tj@...nel.org>,
        Christoph Lameter <cl@...ux.com>
Subject: Re: [RFC Part1 PATCH v3 06/17] x86/mm: Use encrypted access of boot
 related data with SEV

On Mon, Jul 24, 2017 at 02:07:46PM -0500, Brijesh Singh wrote:
> From: Tom Lendacky <thomas.lendacky@....com>
> 
> When Secure Encrypted Virtualization (SEV) is active, boot data (such as
> EFI related data, setup data) is encrypted and needs to be accessed as
> such when mapped. Update the architecture override in early_memremap to
> keep the encryption attribute when mapping this data.
> 
> Signed-off-by: Tom Lendacky <thomas.lendacky@....com>
> Signed-off-by: Brijesh Singh <brijesh.singh@....com>
> ---
>  arch/x86/mm/ioremap.c | 44 ++++++++++++++++++++++++++++++++------------
>  1 file changed, 32 insertions(+), 12 deletions(-)

...

> @@ -590,10 +598,15 @@ bool arch_memremap_can_ram_remap(resource_size_t phys_addr, unsigned long size,
>  	if (flags & MEMREMAP_DEC)
>  		return false;
>  
> -	if (memremap_is_setup_data(phys_addr, size) ||
> -	    memremap_is_efi_data(phys_addr, size) ||
> -	    memremap_should_map_decrypted(phys_addr, size))
> -		return false;
> +	if (sme_active()) {
> +		if (memremap_is_setup_data(phys_addr, size) ||
> +		    memremap_is_efi_data(phys_addr, size) ||
> +		    memremap_should_map_decrypted(phys_addr, size))
> +			return false;
> +	} else if (sev_active()) {
> +		if (memremap_should_map_decrypted(phys_addr, size))
> +			return false;
> +	}
>  
>  	return true;
>  }

I guess this function's hind part can be simplified to:

        if (sme_active()) {
                if (memremap_is_setup_data(phys_addr, size) ||
                    memremap_is_efi_data(phys_addr, size))
                        return false;
        }

        return ! memremap_should_map_decrypted(phys_addr, size);
}

> @@ -608,15 +621,22 @@ pgprot_t __init early_memremap_pgprot_adjust(resource_size_t phys_addr,
>  					     unsigned long size,
>  					     pgprot_t prot)

And this one in a similar manner...

>  {
> -	if (!sme_active())
> +	if (!sme_active() && !sev_active())
>  		return prot;

... and you don't need that check...

> -	if (early_memremap_is_setup_data(phys_addr, size) ||
> -	    memremap_is_efi_data(phys_addr, size) ||
> -	    memremap_should_map_decrypted(phys_addr, size))
> -		prot = pgprot_decrypted(prot);
> -	else
> -		prot = pgprot_encrypted(prot);
> +	if (sme_active()) {

... if you're going to do it here too.

> +		if (early_memremap_is_setup_data(phys_addr, size) ||
> +		    memremap_is_efi_data(phys_addr, size) ||
> +		    memremap_should_map_decrypted(phys_addr, size))
> +			prot = pgprot_decrypted(prot);
> +		else
> +			prot = pgprot_encrypted(prot);
> +	} else if (sev_active()) {

And here.

> +		if (memremap_should_map_decrypted(phys_addr, size))
> +			prot = pgprot_decrypted(prot);
> +		else
> +			prot = pgprot_encrypted(prot);
> +	}

-- 
Regards/Gruss,
    Boris.

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