x86/boot: Add early boot support when running with SEV active

Early in the boot process, add checks to determine if the kernel is
running with Secure Encrypted Virtualization (SEV) active.

Checking for SEV requires checking that the kernel is running under a
hypervisor (CPUID 0x00000001, bit 31), that the SEV feature is available
(CPUID 0x8000001f, bit 1) and then checking a non-interceptable SEV MSR
(0xc0010131, bit 0).

This check is required so that during early compressed kernel booting the
pagetables (both the boot pagetables and KASLR pagetables (if enabled) are
updated to include the encryption mask so that when the kernel is
decompressed into encrypted memory, it can boot properly.

After the kernel is decompressed and continues booting the same logic is
used to check if SEV is active and set a flag indicating so.  This allows
to distinguish between SME and SEV, each of which have unique differences
in how certain things are handled: e.g. DMA (always bounce buffered with
SEV) or EFI tables (always access decrypted with SME).

Signed-off-by: Tom Lendacky <thomas.lendacky@amd.com>
Signed-off-by: Brijesh Singh <brijesh.singh@amd.com>
Signed-off-by: Thomas Gleixner <tglx@linutronix.de>
Reviewed-by: Borislav Petkov <bp@suse.de>
Tested-by: Borislav Petkov <bp@suse.de>
Cc: Laura Abbott <labbott@redhat.com>
Cc: Kees Cook <keescook@chromium.org>
Cc: kvm@vger.kernel.org
Cc: Konrad Rzeszutek Wilk <konrad.wilk@oracle.com>
Cc: Radim Krčmář <rkrcmar@redhat.com>
Cc: Borislav Petkov <bp@alien8.de>
Cc: Andy Lutomirski <luto@kernel.org>
Cc: Paolo Bonzini <pbonzini@redhat.com>
Cc: "Kirill A. Shutemov" <kirill.shutemov@linux.intel.com>
Link: https://lkml.kernel.org/r/20171020143059.3291-13-brijesh.singh@amd.com

1 files changed, 39 insertions, 11 deletions

diff --git a/arch/x86/mm/mem_encrypt.c b/arch/x86/mm/mem_encrypt.c
index e8bfad75ba29..fd9c7bb51664 100644
--- a/arch/x86/mm/mem_encrypt.c
+++ b/arch/x86/mm/mem_encrypt.c
@@ -313,7 +313,9 @@ void __init mem_encrypt_init(void)
 	if (sev_active())
 		dma_ops = &sev_dma_ops;
 
-	pr_info("AMD Secure Memory Encryption (SME) active\n");
+	pr_info("AMD %s active\n",
+		sev_active() ? "Secure Encrypted Virtualization (SEV)"
+			     : "Secure Memory Encryption (SME)");
 }
 
 void swiotlb_set_mem_attributes(void *vaddr, unsigned long size)
@@ -641,37 +643,63 @@ void __init __nostackprotector sme_enable(struct boot_params *bp)
 {
 	const char *cmdline_ptr, *cmdline_arg, *cmdline_on, *cmdline_off;
 	unsigned int eax, ebx, ecx, edx;
+	unsigned long feature_mask;
 	bool active_by_default;
 	unsigned long me_mask;
 	char buffer[16];
 	u64 msr;
 
-	/* Check for the SME support leaf */
+	/* Check for the SME/SEV support leaf */
 	eax = 0x80000000;
 	ecx = 0;
 	native_cpuid(&eax, &ebx, &ecx, &edx);
 	if (eax < 0x8000001f)
 		return;
 
+#define AMD_SME_BIT	BIT(0)
+#define AMD_SEV_BIT	BIT(1)
 	/*
-	 * Check for the SME feature:
-	 *   CPUID Fn8000_001F[EAX] - Bit 0
-	 *     Secure Memory Encryption support
-	 *   CPUID Fn8000_001F[EBX] - Bits 5:0
-	 *     Pagetable bit position used to indicate encryption
+	 * Set the feature mask (SME or SEV) based on whether we are
+	 * running under a hypervisor.
+	 */
+	eax = 1;
+	ecx = 0;
+	native_cpuid(&eax, &ebx, &ecx, &edx);
+	feature_mask = (ecx & BIT(31)) ? AMD_SEV_BIT : AMD_SME_BIT;
+
+	/*
+	 * Check for the SME/SEV feature:
+	 *   CPUID Fn8000_001F[EAX]
+	 *   - Bit 0 - Secure Memory Encryption support
+	 *   - Bit 1 - Secure Encrypted Virtualization support
+	 *   CPUID Fn8000_001F[EBX]
+	 *   - Bits 5:0 - Pagetable bit position used to indicate encryption
 	 */
 	eax = 0x8000001f;
 	ecx = 0;
 	native_cpuid(&eax, &ebx, &ecx, &edx);
-	if (!(eax & 1))
+	if (!(eax & feature_mask))
 		return;
 
 	me_mask = 1UL << (ebx & 0x3f);
 
-	/* Check if SME is enabled */
-	msr = __rdmsr(MSR_K8_SYSCFG);
-	if (!(msr & MSR_K8_SYSCFG_MEM_ENCRYPT))
+	/* Check if memory encryption is enabled */
+	if (feature_mask == AMD_SME_BIT) {
+		/* For SME, check the SYSCFG MSR */
+		msr = __rdmsr(MSR_K8_SYSCFG);
+		if (!(msr & MSR_K8_SYSCFG_MEM_ENCRYPT))
+			return;
+	} else {
+		/* For SEV, check the SEV MSR */
+		msr = __rdmsr(MSR_AMD64_SEV);
+		if (!(msr & MSR_AMD64_SEV_ENABLED))
+			return;
+
+		/* SEV state cannot be controlled by a command line option */
+		sme_me_mask = me_mask;
+		sev_enabled = true;
 		return;
+	}
 
 	/*
 	 * Fixups have not been applied to phys_base yet and we're running