x86/sev: Use firmware-validated CPUID for SEV-SNP guests

SEV-SNP guests will be provided the location of special 'secrets' and
'CPUID' pages via the Confidential Computing blob. This blob is
provided to the run-time kernel either through a boot_params field that
was initialized by the boot/compressed kernel, or via a setup_data
structure as defined by the Linux Boot Protocol.

Locate the Confidential Computing blob from these sources and, if found,
use the provided CPUID page/table address to create a copy that the
run-time kernel will use when servicing CPUID instructions via a #VC
handler.

Signed-off-by: Michael Roth <michael.roth@amd.com>
Signed-off-by: Brijesh Singh <brijesh.singh@amd.com>
Signed-off-by: Borislav Petkov <bp@suse.de>
Link: https://lore.kernel.org/r/20220307213356.2797205-40-brijesh.singh@amd.com

1 files changed, 24 insertions, 0 deletions

diff --git a/arch/x86/kernel/sev.c b/arch/x86/kernel/sev.c
index 692da7b29127..c8733725d8bf 100644
--- a/arch/x86/kernel/sev.c
+++ b/arch/x86/kernel/sev.c
@@ -34,6 +34,7 @@
 #include <asm/cpu.h>
 #include <asm/apic.h>
 #include <asm/cpuid.h>
+#include <asm/cmdline.h>
 
 #define DR7_RESET_VALUE        0x400
 
@@ -2025,6 +2026,8 @@ bool __init snp_init(struct boot_params *bp)
 	if (!cc_info)
 		return false;
 
+	setup_cpuid_table(cc_info);
+
 	/*
 	 * The CC blob will be used later to access the secrets page. Cache
 	 * it here like the boot kernel does.
@@ -2038,3 +2041,24 @@ void __init snp_abort(void)
 {
 	sev_es_terminate(SEV_TERM_SET_GEN, GHCB_SNP_UNSUPPORTED);
 }
+
+/*
+ * It is useful from an auditing/testing perspective to provide an easy way
+ * for the guest owner to know that the CPUID table has been initialized as
+ * expected, but that initialization happens too early in boot to print any
+ * sort of indicator, and there's not really any other good place to do it,
+ * so do it here.
+ */
+static int __init report_cpuid_table(void)
+{
+	const struct snp_cpuid_table *cpuid_table = snp_cpuid_get_table();
+
+	if (!cpuid_table->count)
+		return 0;
+
+	pr_info("Using SNP CPUID table, %d entries present.\n",
+		cpuid_table->count);
+
+	return 0;
+}
+arch_initcall(report_cpuid_table);