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, 120 insertions, 0 deletions

diff --git a/arch/x86/boot/compressed/mem_encrypt.S b/arch/x86/boot/compressed/mem_encrypt.S
new file mode 100644
index 000000000000..54f5f6625a73
--- /dev/null
+++ b/arch/x86/boot/compressed/mem_encrypt.S
@@ -0,0 +1,120 @@
+/*
+ * AMD Memory Encryption Support
+ *
+ * Copyright (C) 2017 Advanced Micro Devices, Inc.
+ *
+ * Author: Tom Lendacky <thomas.lendacky@amd.com>
+ *
+ * This program is free software; you can redistribute it and/or modify
+ * it under the terms of the GNU General Public License version 2 as
+ * published by the Free Software Foundation.
+ */
+
+#include <linux/linkage.h>
+
+#include <asm/processor-flags.h>
+#include <asm/msr.h>
+#include <asm/asm-offsets.h>
+
+	.text
+	.code32
+ENTRY(get_sev_encryption_bit)
+	xor	%eax, %eax
+
+#ifdef CONFIG_AMD_MEM_ENCRYPT
+	push	%ebx
+	push	%ecx
+	push	%edx
+	push	%edi
+
+	/*
+	 * RIP-relative addressing is needed to access the encryption bit
+	 * variable. Since we are running in 32-bit mode we need this call/pop
+	 * sequence to get the proper relative addressing.
+	 */
+	call	1f
+1:	popl	%edi
+	subl	$1b, %edi
+
+	movl	enc_bit(%edi), %eax
+	cmpl	$0, %eax
+	jge	.Lsev_exit
+
+	/* Check if running under a hypervisor */
+	movl	$1, %eax
+	cpuid
+	bt	$31, %ecx		/* Check the hypervisor bit */
+	jnc	.Lno_sev
+
+	movl	$0x80000000, %eax	/* CPUID to check the highest leaf */
+	cpuid
+	cmpl	$0x8000001f, %eax	/* See if 0x8000001f is available */
+	jb	.Lno_sev
+
+	/*
+	 * Check for the SEV feature:
+	 *   CPUID Fn8000_001F[EAX] - Bit 1
+	 *   CPUID Fn8000_001F[EBX] - Bits 5:0
+	 *     Pagetable bit position used to indicate encryption
+	 */
+	movl	$0x8000001f, %eax
+	cpuid
+	bt	$1, %eax		/* Check if SEV is available */
+	jnc	.Lno_sev
+
+	movl	$MSR_AMD64_SEV, %ecx	/* Read the SEV MSR */
+	rdmsr
+	bt	$MSR_AMD64_SEV_ENABLED_BIT, %eax	/* Check if SEV is active */
+	jnc	.Lno_sev
+
+	movl	%ebx, %eax
+	andl	$0x3f, %eax		/* Return the encryption bit location */
+	movl	%eax, enc_bit(%edi)
+	jmp	.Lsev_exit
+
+.Lno_sev:
+	xor	%eax, %eax
+	movl	%eax, enc_bit(%edi)
+
+.Lsev_exit:
+	pop	%edi
+	pop	%edx
+	pop	%ecx
+	pop	%ebx
+
+#endif	/* CONFIG_AMD_MEM_ENCRYPT */
+
+	ret
+ENDPROC(get_sev_encryption_bit)
+
+	.code64
+ENTRY(get_sev_encryption_mask)
+	xor	%rax, %rax
+
+#ifdef CONFIG_AMD_MEM_ENCRYPT
+	push	%rbp
+	push	%rdx
+
+	movq	%rsp, %rbp		/* Save current stack pointer */
+
+	call	get_sev_encryption_bit	/* Get the encryption bit position */
+	testl	%eax, %eax
+	jz	.Lno_sev_mask
+
+	xor	%rdx, %rdx
+	bts	%rax, %rdx		/* Create the encryption mask */
+	mov	%rdx, %rax		/* ... and return it */
+
+.Lno_sev_mask:
+	movq	%rbp, %rsp		/* Restore original stack pointer */
+
+	pop	%rdx
+	pop	%rbp
+#endif
+
+	ret
+ENDPROC(get_sev_encryption_mask)
+
+	.data
+enc_bit:
+	.int	0xffffffff