linux-kernel - Re: [RFC PATCH v3 20/20] x86: Add support to make use of Secure Memory Encryption

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Date:   Sat, 26 Nov 2016 21:47:03 +0100
From:   Borislav Petkov <bp@...en8.de>
To:     Tom Lendacky <thomas.lendacky@....com>
Cc:     linux-arch@...r.kernel.org, linux-efi@...r.kernel.org,
        kvm@...r.kernel.org, linux-doc@...r.kernel.org, x86@...nel.org,
        linux-kernel@...r.kernel.org, kasan-dev@...glegroups.com,
        linux-mm@...ck.org, iommu@...ts.linux-foundation.org,
        Rik van Riel <riel@...hat.com>,
        Radim Krčmář <rkrcmar@...hat.com>,
        Arnd Bergmann <arnd@...db.de>,
        Jonathan Corbet <corbet@....net>,
        Matt Fleming <matt@...eblueprint.co.uk>,
        Joerg Roedel <joro@...tes.org>,
        Konrad Rzeszutek Wilk <konrad.wilk@...cle.com>,
        Paolo Bonzini <pbonzini@...hat.com>,
        Larry Woodman <lwoodman@...hat.com>,
        Ingo Molnar <mingo@...hat.com>,
        Andy Lutomirski <luto@...nel.org>,
        "H. Peter Anvin" <hpa@...or.com>,
        Andrey Ryabinin <aryabinin@...tuozzo.com>,
        Alexander Potapenko <glider@...gle.com>,
        Thomas Gleixner <tglx@...utronix.de>,
        Dmitry Vyukov <dvyukov@...gle.com>
Subject: Re: [RFC PATCH v3 20/20] x86: Add support to make use of Secure
 Memory Encryption

On Wed, Nov 09, 2016 at 06:38:38PM -0600, Tom Lendacky wrote:
> This patch adds the support to check if SME has been enabled and if the
> mem_encrypt=on command line option is set. If both of these conditions
> are true, then the encryption mask is set and the kernel is encrypted
> "in place."
> 
> Signed-off-by: Tom Lendacky <thomas.lendacky@....com>
> ---
>  arch/x86/kernel/head_64.S          |    1 +
>  arch/x86/kernel/mem_encrypt_init.c |   60 +++++++++++++++++++++++++++++++++++-
>  arch/x86/mm/mem_encrypt.c          |    2 +
>  3 files changed, 62 insertions(+), 1 deletion(-)
> 
> diff --git a/arch/x86/kernel/head_64.S b/arch/x86/kernel/head_64.S
> index e8a7272..c225433 100644
> --- a/arch/x86/kernel/head_64.S
> +++ b/arch/x86/kernel/head_64.S
> @@ -100,6 +100,7 @@ startup_64:
>  	 * to include it in the page table fixups.
>  	 */
>  	push	%rsi
> +	movq	%rsi, %rdi
>  	call	sme_enable
>  	pop	%rsi
>  	movq	%rax, %r12
> diff --git a/arch/x86/kernel/mem_encrypt_init.c b/arch/x86/kernel/mem_encrypt_init.c
> index 7bdd159..c94ceb8 100644
> --- a/arch/x86/kernel/mem_encrypt_init.c
> +++ b/arch/x86/kernel/mem_encrypt_init.c
> @@ -16,9 +16,14 @@
>  #include <linux/mm.h>
>  
>  #include <asm/sections.h>
> +#include <asm/processor-flags.h>
> +#include <asm/msr.h>
> +#include <asm/cmdline.h>
>  
>  #ifdef CONFIG_AMD_MEM_ENCRYPT
>  
> +static char sme_cmdline_arg[] __initdata = "mem_encrypt=on";

One more thing: just like we're adding an =on switch, we'd need an =off
switch in case something's wrong with the SME code. IOW, if a user
supplies "mem_encrypt=off", we do not encrypt.

Thanks.

-- 
Regards/Gruss,
    Boris.

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