linux-kernel - Re: [RFC PATCH v2 02/32] x86: Secure Encrypted Virtualization (SEV) support

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Message-ID: <20170308150603.5n4efpylat5i7rgb@pd.tnic>
Date:   Wed, 8 Mar 2017 16:06:03 +0100
From:   Borislav Petkov <bp@...e.de>
To:     Brijesh Singh <brijesh.singh@....com>
Cc:     simon.guinot@...uanux.org, linux-efi@...r.kernel.org,
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Subject: Re: [RFC PATCH v2 02/32] x86: Secure Encrypted Virtualization (SEV)
 support

On Thu, Mar 02, 2017 at 10:12:20AM -0500, Brijesh Singh wrote:
> From: Tom Lendacky <thomas.lendacky@....com>
> 
> Provide support for Secure Encyrpted Virtualization (SEV). This initial
> support defines a flag that is used by the kernel to determine if it is
> running with SEV active.
> 
> Signed-off-by: Tom Lendacky <thomas.lendacky@....com>
> ---
>  arch/x86/include/asm/mem_encrypt.h |   14 +++++++++++++-
>  arch/x86/mm/mem_encrypt.c          |    3 +++
>  include/linux/mem_encrypt.h        |    6 ++++++
>  3 files changed, 22 insertions(+), 1 deletion(-)
> 
> diff --git a/arch/x86/include/asm/mem_encrypt.h b/arch/x86/include/asm/mem_encrypt.h
> index 1fd5426..9799835 100644
> --- a/arch/x86/include/asm/mem_encrypt.h
> +++ b/arch/x86/include/asm/mem_encrypt.h
> @@ -20,10 +20,16 @@
>  #ifdef CONFIG_AMD_MEM_ENCRYPT
>  
>  extern unsigned long sme_me_mask;
> +extern unsigned int sev_enabled;

So there's a function name sev_enabled() and an int sev_enabled too.

It looks to me like you want to call the function "sev_enable()" -
similar to sme_enable(), convert it to C code - i.e., I don't see what
would speak against it - and rename that sev_enc_bit to sev_enabled and
use it everywhere when testing SEV status.

>  static inline bool sme_active(void)
>  {
> -	return (sme_me_mask) ? true : false;
> +	return (sme_me_mask && !sev_enabled) ? true : false;
> +}
> +
> +static inline bool sev_active(void)
> +{
> +	return (sme_me_mask && sev_enabled) ? true : false;

Then, those read strange: like SME and SEV are mutually exclusive. Why?
I might have an idea but I'd like for you to confirm it :-)

Then, you're calling sev_enabled in startup_32() but we can enter
in arch/x86/boot/compressed/head_64.S::startup_64() too, when we're
loaded by a 64-bit bootloader, which would then theoretically bypass
sev_enabled().

-- 
Regards/Gruss,
    Boris.

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