x86/boot/compressed/64: Add 32-bit boot #VC handler

Add a #VC exception handler which is used when the kernel still executes
in protected mode. This boot-path already uses CPUID, which will cause #VC
exceptions in an SEV-ES guest.

Signed-off-by: Joerg Roedel <jroedel@suse.de>
Signed-off-by: Borislav Petkov <bp@suse.de>
Link: https://lkml.kernel.org/r/20210312123824.306-6-joro@8bytes.org

1 files changed, 95 insertions, 1 deletions

diff --git a/arch/x86/boot/compressed/mem_encrypt.S b/arch/x86/boot/compressed/mem_encrypt.S
index a6dea4e8a082..ebc4a29fb18a 100644
--- a/arch/x86/boot/compressed/mem_encrypt.S
+++ b/arch/x86/boot/compressed/mem_encrypt.S
@@ -61,10 +61,104 @@ SYM_FUNC_START(get_sev_encryption_bit)
 	ret
 SYM_FUNC_END(get_sev_encryption_bit)
 
+/**
+ * sev_es_req_cpuid - Request a CPUID value from the Hypervisor using
+ *		      the GHCB MSR protocol
+ *
+ * @%eax:	Register to request (0=EAX, 1=EBX, 2=ECX, 3=EDX)
+ * @%edx:	CPUID Function
+ *
+ * Returns 0 in %eax on success, non-zero on failure
+ * %edx returns CPUID value on success
+ */
+SYM_CODE_START_LOCAL(sev_es_req_cpuid)
+	shll	$30, %eax
+	orl     $0x00000004, %eax
+	movl    $MSR_AMD64_SEV_ES_GHCB, %ecx
+	wrmsr
+	rep; vmmcall		# VMGEXIT
+	rdmsr
+
+	/* Check response */
+	movl	%eax, %ecx
+	andl	$0x3ffff000, %ecx	# Bits [12-29] MBZ
+	jnz	2f
+
+	/* Check return code */
+	andl    $0xfff, %eax
+	cmpl    $5, %eax
+	jne	2f
+
+	/* All good - return success */
+	xorl	%eax, %eax
+1:
+	ret
+2:
+	movl	$-1, %eax
+	jmp	1b
+SYM_CODE_END(sev_es_req_cpuid)
+
+SYM_CODE_START(startup32_vc_handler)
+	pushl	%eax
+	pushl	%ebx
+	pushl	%ecx
+	pushl	%edx
+
+	/* Keep CPUID function in %ebx */
+	movl	%eax, %ebx
+
+	/* Check if error-code == SVM_EXIT_CPUID */
+	cmpl	$0x72, 16(%esp)
+	jne	.Lfail
+
+	movl	$0, %eax		# Request CPUID[fn].EAX
+	movl	%ebx, %edx		# CPUID fn
+	call	sev_es_req_cpuid	# Call helper
+	testl	%eax, %eax		# Check return code
+	jnz	.Lfail
+	movl	%edx, 12(%esp)		# Store result
+
+	movl	$1, %eax		# Request CPUID[fn].EBX
+	movl	%ebx, %edx		# CPUID fn
+	call	sev_es_req_cpuid	# Call helper
+	testl	%eax, %eax		# Check return code
+	jnz	.Lfail
+	movl	%edx, 8(%esp)		# Store result
+
+	movl	$2, %eax		# Request CPUID[fn].ECX
+	movl	%ebx, %edx		# CPUID fn
+	call	sev_es_req_cpuid	# Call helper
+	testl	%eax, %eax		# Check return code
+	jnz	.Lfail
+	movl	%edx, 4(%esp)		# Store result
+
+	movl	$3, %eax		# Request CPUID[fn].EDX
+	movl	%ebx, %edx		# CPUID fn
+	call	sev_es_req_cpuid	# Call helper
+	testl	%eax, %eax		# Check return code
+	jnz	.Lfail
+	movl	%edx, 0(%esp)		# Store result
+
+	popl	%edx
+	popl	%ecx
+	popl	%ebx
+	popl	%eax
+
+	/* Remove error code */
+	addl	$4, %esp
+
+	/* Jump over CPUID instruction */
+	addl	$2, (%esp)
+
+	iret
+.Lfail:
+	hlt
+	jmp .Lfail
+SYM_CODE_END(startup32_vc_handler)
+
 	.code64
 
 #include "../../kernel/sev_verify_cbit.S"
-
 SYM_FUNC_START(set_sev_encryption_mask)
 #ifdef CONFIG_AMD_MEM_ENCRYPT
 	push	%rbp