From: "Limonciello, Mario" <mario.limonciello@amd.com>
To: Tom Lendacky <thomas.lendacky@amd.com>,
Borislav Petkov <bp@alien8.de>,
"maintainer:X86 ARCHITECTURE (32-BIT AND 64-BIT)"
<x86@kernel.org>
Cc: Kees Cook <keescook@chromium.org>,
hughsient@gmail.com,
Martin Fernandez <martin.fernandez@eclypsium.com>,
linux-kernel@vger.kernel.org,
Brijesh Singh <brijesh.singh@amd.com>
Subject: Re: [PATCH 2/2] x86/cpu: clear SME/SEV/SEV_ES features when not in use
Date: Fri, 11 Feb 2022 13:54:01 -0600 [thread overview]
Message-ID: <d705b64d-2866-e2bf-2323-dfe0cfe73da8@amd.com> (raw)
In-Reply-To: <4035f596-651c-c167-372b-ffb8ce1a0ac7@amd.com>
On 2/11/2022 08:46, Tom Lendacky wrote:
> +Brijesh (please copy him, too, on all SEV related things)
>
> On 2/10/22 23:36, 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@amd.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;
>> +
>
> A host/hypervisor will never see GUEST related attributes return true,
> you need to verify all uses of X86_FEATURE_SEV* in the kernel. I see two
> files where this change will break SEV hypervisor support:
>
Maybe it's best then to just check for/clear the SME feature at this
time and let Brijesh handle plumbing the applicable removals/additions
for SEV/SEV_ES separately.
> - arch/x86/kvm/svm/sev.c / sev_hardware_setup()
> - drivers/crypto/ccp/sev-dev.c / sev_dev_init()
>
> I imagine that some of this has to be re-thought a bit. The current SEV
> and SEV-ES feature attributes are intended for hypervsior side usage.
> For example, MSR MSR_K7_HWCR_SMMLOCK, which is likely never going to be
> provided to a guest, needs to be checked to be certain that an SEV guest
> can be launched, even though SEV is advertised in CPUID.
>
> Once in the guest, it is the cc_platform_has() support that determines
> feature support and not X86_FEATURE_SEV*
>
> Thanks,
> Tom
>
>> return;
>> clear_all:
>> setup_clear_cpu_cap(X86_FEATURE_SME);
>> clear_sev:
>> setup_clear_cpu_cap(X86_FEATURE_SEV);
>> +clear_sev_es:
>> setup_clear_cpu_cap(X86_FEATURE_SEV_ES);
>> }
>> }
next prev parent reply other threads:[~2022-02-11 19:54 UTC|newest]
Thread overview: 11+ messages / expand[flat|nested] mbox.gz Atom feed top
2022-02-11 5:36 [PATCH 1/2] x86: Use CPUID 0x8000001f to confirm SME availability Mario Limonciello
2022-02-11 5:36 ` [PATCH 2/2] x86/cpu: clear SME/SEV/SEV_ES features when not in use Mario Limonciello
2022-02-11 8:31 ` Borislav Petkov
2022-02-11 19:43 ` Limonciello, Mario
2022-02-11 14:46 ` Tom Lendacky
2022-02-11 19:54 ` Limonciello, Mario [this message]
2022-02-11 20:42 ` Tom Lendacky
2022-02-11 8:28 ` [PATCH 1/2] x86: Use CPUID 0x8000001f to confirm SME availability Borislav Petkov
2022-02-11 14:55 ` Tom Lendacky
2022-02-11 19:51 ` Limonciello, Mario
2022-02-11 21:09 ` Tom Lendacky
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