linux-kernel - Re: [PATCH 2/2] x86/cpu: clear SME/SEV/SEV

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Date:   Fri, 11 Feb 2022 09:31:17 +0100
From:   Borislav Petkov <bp@...en8.de>
To:     Mario Limonciello <mario.limonciello@....com>
Cc:     "maintainer:X86 ARCHITECTURE (32-BIT AND 64-BIT)" <x86@...nel.org>,
        Kees Cook <keescook@...omium.org>,
        Thomas Lendacky <Thomas.Lendacky@....com>, hughsient@...il.com,
        Martin Fernandez <martin.fernandez@...ypsium.com>,
        linux-kernel@...r.kernel.org
Subject: Re: [PATCH 2/2] x86/cpu: clear SME/SEV/SEV_ES features when not in
 use

On Thu, Feb 10, 2022 at 11:36:52PM -0600, Mario Limonciello wrote:
> Currently SME/SEV/SEV_ES features are reflective of whether the CPU
> supports the features but not whether they have been activated by the
> kernel.
> 
> Change this around to clear the features if the kernel is not using
> them so userspace can determine if they are available and in use
> from `/proc/cpuinfo`.
> 
> Signed-off-by: Mario Limonciello <mario.limonciello@....com>
> ---
>  arch/x86/kernel/cpu/amd.c | 8 ++++++++
>  1 file changed, 8 insertions(+)
> 
> diff --git a/arch/x86/kernel/cpu/amd.c b/arch/x86/kernel/cpu/amd.c
> index 4edb6f0f628c..4a7d4801fa0b 100644
> --- a/arch/x86/kernel/cpu/amd.c
> +++ b/arch/x86/kernel/cpu/amd.c
> @@ -611,12 +611,20 @@ static void early_detect_mem_encrypt(struct cpuinfo_x86 *c)
>  		if (!(msr & MSR_K7_HWCR_SMMLOCK))
>  			goto clear_sev;
>  
> +		if (!cc_platform_has(CC_ATTR_MEM_ENCRYPT))
> +			goto clear_all;
> +		if (!cc_platform_has(CC_ATTR_GUEST_MEM_ENCRYPT))
> +			goto clear_sev;
> +		if (!cc_platform_has(CC_ATTR_GUEST_STATE_ENCRYPT))
> +			goto clear_sev_es;

The cc_platform stuff is to be used in generic code - I think you can
safely read MSR_AMD64_SEV here and look at the bits, just like the rest
of this code does.

Also, why is this a separate patch? I.e., one single patch should be
just fine.

Thx.

-- 
Regards/Gruss,
    Boris.

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