Re: [RFC Part1 PATCH 01/13] x86/cpufeatures: Add SEV-SNP CPU feature

Borislav Petkov
2021-03-25T10:54:59Z

On Wed, Mar 24, 2021 at 11:44:12AM -0500, Brijesh Singh wrote:
> Add CPU feature detection for Secure Encrypted Virtualization with
> Secure Nested Paging. This feature adds a strong memory integrity
> protection to help prevent malicious hypervisor-based attacks like
> data replay, memory re-mapping, and more.
>
> Cc: Thomas Gleixner <tglx@linutronix.de>
> Cc: Ingo Molnar <mingo@redhat.com>
> Cc: Borislav Petkov <bp@alien8.de>
> Cc: Joerg Roedel <jroedel@suse.de>
> Cc: "H. Peter Anvin" <hpa@zytor.com>
> Cc: Tony Luck <tony.luck@intel.com>
> Cc: Dave Hansen <dave.hansen@intel.com>
> Cc: "Peter Zijlstra (Intel)" <peterz@infradead.org>
> Cc: Paolo Bonzini <pbonzini@redhat.com>
> Cc: Tom Lendacky <thomas.lendacky@amd.com>
> Cc: David Rientjes <rientjes@google.com>
> Cc: Sean Christopherson <seanjc@google.com>
> Cc: x86@kernel.org
> Cc: kvm@vger.kernel.org
> Signed-off-by: Brijesh Singh <brijesh.singh@amd.com>
> ---
> arch/x86/include/asm/cpufeatures.h | 1 +
> arch/x86/kernel/cpu/amd.c | 3 ++-
> arch/x86/kernel/cpu/scattered.c | 1 +
> 3 files changed, 4 insertions(+), 1 deletion(-)
>
> diff --git a/arch/x86/include/asm/cpufeatures.h b/arch/x86/include/asm/cpufeatures.h
> index 84b887825f12..a5b369f10bcd 100644
> --- a/arch/x86/include/asm/cpufeatures.h
> +++ b/arch/x86/include/asm/cpufeatures.h
> @@ -238,6 +238,7 @@
> #define X86_FEATURE_VMW_VMMCALL ( 8*32+19) /* "" VMware prefers VMMCALL hypercall instruction */
> #define X86_FEATURE_SEV_ES ( 8*32+20) /* AMD Secure Encrypted Virtualization - Encrypted State */
> #define X86_FEATURE_VM_PAGE_FLUSH ( 8*32+21) /* "" VM Page Flush MSR is supported */
> +#define X86_FEATURE_SEV_SNP ( 8*32+22) /* AMD Secure Encrypted Virtualization - Secure Nested Paging */

That leaf got a separate word now: word 19.

For the future: pls redo your patches against tip/master because it has
the latest state of affairs in tip-land.

> /* Intel-defined CPU features, CPUID level 0x00000007:0 (EBX), word 9 */
> #define X86_FEATURE_FSGSBASE ( 9*32+ 0) /* RDFSBASE, WRFSBASE, RDGSBASE, WRGSBASE instructions*/
> diff --git a/arch/x86/kernel/cpu/amd.c b/arch/x86/kernel/cpu/amd.c
> index f8ca66f3d861..39f7a4b5b04c 100644
> --- a/arch/x86/kernel/cpu/amd.c
> +++ b/arch/x86/kernel/cpu/amd.c
> @@ -586,7 +586,7 @@ static void early_detect_mem_encrypt(struct cpuinfo_x86 *c)
> * If BIOS has not enabled SME then don't advertise the
> * SME feature (set in scattered.c).
> * For SEV: If BIOS has not enabled SEV then don't advertise the
> - * SEV and SEV_ES feature (set in scattered.c).
> + * SEV, SEV_ES and SEV_SNP feature (set in scattered.c).

So you can remove the "scattered.c" references in the comments here.

> *
> * In all cases, since support for SME and SEV requires long mode,
> * don't advertise the feature under CONFIG_X86_32.
> @@ -618,6 +618,7 @@ static void early_detect_mem_encrypt(struct cpuinfo_x86 *c)
> clear_sev:
> setup_clear_cpu_cap(X86_FEATURE_SEV);
> setup_clear_cpu_cap(X86_FEATURE_SEV_ES);
> + setup_clear_cpu_cap(X86_FEATURE_SEV_SNP);
> }
> }
>
> diff --git a/arch/x86/kernel/cpu/scattered.c b/arch/x86/kernel/cpu/scattered.c
> index 236924930bf0..eaec1278dc2e 100644
> --- a/arch/x86/kernel/cpu/scattered.c
> +++ b/arch/x86/kernel/cpu/scattered.c
> @@ -45,6 +45,7 @@ static const struct cpuid_bit cpuid_bits[] = {
> { X86_FEATURE_SEV_ES, CPUID_EAX, 3, 0x8000001f, 0 },
> { X86_FEATURE_SME_COHERENT, CPUID_EAX, 10, 0x8000001f, 0 },
> { X86_FEATURE_VM_PAGE_FLUSH, CPUID_EAX, 2, 0x8000001f, 0 },
> + { X86_FEATURE_SEV_SNP, CPUID_EAX, 4, 0x8000001f, 0 },
> { 0, 0, 0, 0, 0 }
> };

And this too.

Thx.

--
Regards/Gruss,
Boris.