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

arch/x86/boot/compressed/sev.c

@@ -381,43 +381,6 @@ static struct cc_blob_sev_info *find_cc_blob(struct boot_params *bp)
 	return cc_info;
 }
 
-/*
- * Initialize the kernel's copy of the SNP CPUID table, and set up the
- * pointer that will be used to access it.
- *
- * Maintaining a direct mapping of the SNP CPUID table used by firmware would
- * be possible as an alternative, but the approach is brittle since the
- * mapping needs to be updated in sync with all the changes to virtual memory
- * layout and related mapping facilities throughout the boot process.
- */
-static void setup_cpuid_table(const struct cc_blob_sev_info *cc_info)
-{
-	const struct snp_cpuid_table *cpuid_table_fw, *cpuid_table;
-	int i;
-
-	if (!cc_info || !cc_info->cpuid_phys || cc_info->cpuid_len < PAGE_SIZE)
-		sev_es_terminate(SEV_TERM_SET_LINUX, GHCB_TERM_CPUID);
-
-	cpuid_table_fw = (const struct snp_cpuid_table *)cc_info->cpuid_phys;
-	if (!cpuid_table_fw->count || cpuid_table_fw->count > SNP_CPUID_COUNT_MAX)
-		sev_es_terminate(SEV_TERM_SET_LINUX, GHCB_TERM_CPUID);
-
-	cpuid_table = snp_cpuid_get_table();
-	memcpy((void *)cpuid_table, cpuid_table_fw, sizeof(*cpuid_table));
-
-	/* Initialize CPUID ranges for range-checking. */
-	for (i = 0; i < cpuid_table->count; i++) {
-		const struct snp_cpuid_fn *fn = &cpuid_table->fn[i];
-
-		if (fn->eax_in == 0x0)
-			cpuid_std_range_max = fn->eax;
-		else if (fn->eax_in == 0x40000000)
-			cpuid_hyp_range_max = fn->eax;
-		else if (fn->eax_in == 0x80000000)
-			cpuid_ext_range_max = fn->eax;
-	}
-}
-
 /*
  * Indicate SNP based on presence of SNP-specific CC blob. Subsequent checks
  * will verify the SNP CPUID/MSR bits.

arch/x86/kernel/sev-shared.c

@@ -964,3 +964,40 @@ static struct cc_blob_sev_info *find_cc_blob_setup_data(struct boot_params *bp)
 
 	return NULL;
 }
+
+/*
+ * Initialize the kernel's copy of the SNP CPUID table, and set up the
+ * pointer that will be used to access it.
+ *
+ * Maintaining a direct mapping of the SNP CPUID table used by firmware would
+ * be possible as an alternative, but the approach is brittle since the
+ * mapping needs to be updated in sync with all the changes to virtual memory
+ * layout and related mapping facilities throughout the boot process.
+ */
+static void __init setup_cpuid_table(const struct cc_blob_sev_info *cc_info)
+{
+	const struct snp_cpuid_table *cpuid_table_fw, *cpuid_table;
+	int i;
+
+	if (!cc_info || !cc_info->cpuid_phys || cc_info->cpuid_len < PAGE_SIZE)
+		sev_es_terminate(SEV_TERM_SET_LINUX, GHCB_TERM_CPUID);
+
+	cpuid_table_fw = (const struct snp_cpuid_table *)cc_info->cpuid_phys;
+	if (!cpuid_table_fw->count || cpuid_table_fw->count > SNP_CPUID_COUNT_MAX)
+		sev_es_terminate(SEV_TERM_SET_LINUX, GHCB_TERM_CPUID);
+
+	cpuid_table = snp_cpuid_get_table();
+	memcpy((void *)cpuid_table, cpuid_table_fw, sizeof(*cpuid_table));
+
+	/* Initialize CPUID ranges for range-checking. */
+	for (i = 0; i < cpuid_table->count; i++) {
+		const struct snp_cpuid_fn *fn = &cpuid_table->fn[i];
+
+		if (fn->eax_in == 0x0)
+			cpuid_std_range_max = fn->eax;
+		else if (fn->eax_in == 0x40000000)
+			cpuid_hyp_range_max = fn->eax;
+		else if (fn->eax_in == 0x80000000)
+			cpuid_ext_range_max = fn->eax;
+	}
+}

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);