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

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Date:   Fri, 11 Feb 2022 13:43:09 -0600
From:   "Limonciello, Mario" <mario.limonciello@....com>
To:     Borislav Petkov <bp@...en8.de>
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 2/11/2022 02:31, Borislav Petkov wrote:
> 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.

Yeah I was just looking to avoid the code duplication in multiple parts 
of the kernel.  If it's preferable to just duplicate the logic that 
cc_platform_has here for the AMD platform, I'll do that instead.

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

Very well, will squash them.