i386/sev: Allow measured direct kernel boot on SNP

In SNP, the hashes page designated with a specific metadata entry
published in AmdSev OVMF.

Therefore, if the user enabled kernel hashes (for measured direct boot),
QEMU should prepare the content of hashes table, and during the
processing of the metadata entry it copy the content into the designated
page and encrypt it.

Note that in SNP (unlike SEV and SEV-ES) the measurements is done in
whole 4KB pages.  Therefore QEMU zeros the whole page that includes the
hashes table, and fills in the kernel hashes area in that page, and then
encrypts the whole page.  The rest of the page is reserved for SEV
launch secrets which are not usable anyway on SNP.

If the user disabled kernel hashes, QEMU pre-validates the kernel hashes
page as a zero page.

Signed-off-by: Dov Murik <dovmurik@linux.ibm.com>
Signed-off-by: Michael Roth <michael.roth@amd.com>
Signed-off-by: Pankaj Gupta <pankaj.gupta@amd.com>
Message-ID: <20240530111643.1091816-24-pankaj.gupta@amd.com>
Signed-off-by: Paolo Bonzini <pbonzini@redhat.com>

diff --git a/include/hw/i386/pc.h b/include/hw/i386/pc.h
index c653b8eeb2404db366acec803a2c9ebeee946b13..ca7904ac2c4555997db643825b140d2256785266 100644 (file)
--- a/include/hw/i386/pc.h
+++ b/include/hw/i386/pc.h
@@ -172,6 +172,8 @@ typedef enum {
     SEV_DESC_TYPE_SNP_SECRETS,
     /* The section contains address that can be used as a CPUID page */
     SEV_DESC_TYPE_CPUID,
+    /* The section contains the region for kernel hashes for measured direct boot */
+    SEV_DESC_TYPE_SNP_KERNEL_HASHES = 0x10,
 
 } ovmf_sev_metadata_desc_type;
 

diff --git a/target/i386/sev.c b/target/i386/sev.c
index 3fce4c08ebb481dffe548ccb56c3438186f9d198..004c667ac144851eadccc39b61e68d3c1d374ac2 100644 (file)
--- a/target/i386/sev.c
+++ b/target/i386/sev.c
@@ -115,6 +115,10 @@ struct SevCommonStateClass {
     X86ConfidentialGuestClass parent_class;
 
     /* public */
+    bool (*build_kernel_loader_hashes)(SevCommonState *sev_common,
+                                       SevHashTableDescriptor *area,
+                                       SevKernelLoaderContext *ctx,
+                                       Error **errp);
     int (*launch_start)(SevCommonState *sev_common);
     void (*launch_finish)(SevCommonState *sev_common);
     int (*launch_update_data)(SevCommonState *sev_common, hwaddr gpa, uint8_t *ptr, uint64_t len);
@@ -154,6 +158,9 @@ struct SevSnpGuestState {
 
     struct kvm_sev_snp_launch_start kvm_start_conf;
     struct kvm_sev_snp_launch_finish kvm_finish_conf;
+
+    uint32_t kernel_hashes_offset;
+    PaddedSevHashTable *kernel_hashes_data;
 };
 
 #define DEFAULT_GUEST_POLICY    0x1 /* disable debug */
@@ -1189,6 +1196,23 @@ snp_launch_update_cpuid(uint32_t cpuid_addr, void *hva, uint32_t cpuid_len)
                                   KVM_SEV_SNP_PAGE_TYPE_CPUID);
 }
 
+static int
+snp_launch_update_kernel_hashes(SevSnpGuestState *sev_snp, uint32_t addr,
+                                void *hva, uint32_t len)
+{
+    int type = KVM_SEV_SNP_PAGE_TYPE_ZERO;
+    if (sev_snp->parent_obj.kernel_hashes) {
+        assert(sev_snp->kernel_hashes_data);
+        assert((sev_snp->kernel_hashes_offset +
+                sizeof(*sev_snp->kernel_hashes_data)) <= len);
+        memset(hva, 0, len);
+        memcpy(hva + sev_snp->kernel_hashes_offset, sev_snp->kernel_hashes_data,
+               sizeof(*sev_snp->kernel_hashes_data));
+        type = KVM_SEV_SNP_PAGE_TYPE_NORMAL;
+    }
+    return snp_launch_update_data(addr, hva, len, type);
+}
+
 static int
 snp_metadata_desc_to_page_type(int desc_type)
 {
@@ -1225,6 +1249,9 @@ snp_populate_metadata_pages(SevSnpGuestState *sev_snp,
 
         if (type == KVM_SEV_SNP_PAGE_TYPE_CPUID) {
             ret = snp_launch_update_cpuid(desc->base, hva, desc->len);
+        } else if (desc->type == SEV_DESC_TYPE_SNP_KERNEL_HASHES) {
+            ret = snp_launch_update_kernel_hashes(sev_snp, desc->base, hva,
+                                                  desc->len);
         } else {
             ret = snp_launch_update_data(desc->base, hva, desc->len, type);
         }
@@ -1823,6 +1850,58 @@ static bool build_kernel_loader_hashes(PaddedSevHashTable *padded_ht,
     return true;
 }
 
+static bool sev_snp_build_kernel_loader_hashes(SevCommonState *sev_common,
+                                               SevHashTableDescriptor *area,
+                                               SevKernelLoaderContext *ctx,
+                                               Error **errp)
+{
+    /*
+     * SNP: Populate the hashes table in an area that later in
+     * snp_launch_update_kernel_hashes() will be copied to the guest memory
+     * and encrypted.
+     */
+    SevSnpGuestState *sev_snp_guest = SEV_SNP_GUEST(sev_common);
+    sev_snp_guest->kernel_hashes_offset = area->base & ~TARGET_PAGE_MASK;
+    sev_snp_guest->kernel_hashes_data = g_new0(PaddedSevHashTable, 1);
+    return build_kernel_loader_hashes(sev_snp_guest->kernel_hashes_data, ctx, errp);
+}
+
+static bool sev_build_kernel_loader_hashes(SevCommonState *sev_common,
+                                           SevHashTableDescriptor *area,
+                                           SevKernelLoaderContext *ctx,
+                                           Error **errp)
+{
+    PaddedSevHashTable *padded_ht;
+    hwaddr mapped_len = sizeof(*padded_ht);
+    MemTxAttrs attrs = { 0 };
+    bool ret = true;
+
+    /*
+     * Populate the hashes table in the guest's memory at the OVMF-designated
+     * area for the SEV hashes table
+     */
+    padded_ht = address_space_map(&address_space_memory, area->base,
+                                  &mapped_len, true, attrs);
+    if (!padded_ht || mapped_len != sizeof(*padded_ht)) {
+        error_setg(errp, "SEV: cannot map hashes table guest memory area");
+        return false;
+    }
+
+    if (build_kernel_loader_hashes(padded_ht, ctx, errp)) {
+        if (sev_encrypt_flash(area->base, (uint8_t *)padded_ht,
+                              sizeof(*padded_ht), errp) < 0) {
+            ret = false;
+        }
+    } else {
+        ret = false;
+    }
+
+    address_space_unmap(&address_space_memory, padded_ht,
+                        mapped_len, true, mapped_len);
+
+    return ret;
+}
+
 /*
  * Add the hashes of the linux kernel/initrd/cmdline to an encrypted guest page
  * which is included in SEV's initial memory measurement.
@@ -1831,11 +1910,8 @@ bool sev_add_kernel_loader_hashes(SevKernelLoaderContext *ctx, Error **errp)
 {
     uint8_t *data;
     SevHashTableDescriptor *area;
-    PaddedSevHashTable *padded_ht;
-    hwaddr mapped_len = sizeof(*padded_ht);
-    MemTxAttrs attrs = { 0 };
-    bool ret = true;
     SevCommonState *sev_common = SEV_COMMON(MACHINE(qdev_get_machine())->cgs);
+    SevCommonStateClass *klass = SEV_COMMON_GET_CLASS(sev_common);
 
     /*
      * Only add the kernel hashes if the sev-guest configuration explicitly
@@ -1858,30 +1934,7 @@ bool sev_add_kernel_loader_hashes(SevKernelLoaderContext *ctx, Error **errp)
         return false;
     }
 
-    /*
-     * Populate the hashes table in the guest's memory at the OVMF-designated
-     * area for the SEV hashes table
-     */
-    padded_ht = address_space_map(&address_space_memory, area->base,
-                                  &mapped_len, true, attrs);
-    if (!padded_ht || mapped_len != sizeof(*padded_ht)) {
-        error_setg(errp, "SEV: cannot map hashes table guest memory area");
-        return false;
-    }
-
-    if (build_kernel_loader_hashes(padded_ht, ctx, errp)) {
-        if (sev_encrypt_flash(area->base, (uint8_t *)padded_ht,
-                              sizeof(*padded_ht), errp) < 0) {
-            ret = false;
-        }
-    } else {
-        ret = false;
-    }
-
-    address_space_unmap(&address_space_memory, padded_ht,
-                        mapped_len, true, mapped_len);
-
-    return ret;
+    return klass->build_kernel_loader_hashes(sev_common, area, ctx, errp);
 }
 
 static char *
@@ -1998,6 +2051,7 @@ sev_guest_class_init(ObjectClass *oc, void *data)
     SevCommonStateClass *klass = SEV_COMMON_CLASS(oc);
     X86ConfidentialGuestClass *x86_klass = X86_CONFIDENTIAL_GUEST_CLASS(oc);
 
+    klass->build_kernel_loader_hashes = sev_build_kernel_loader_hashes;
     klass->launch_start = sev_launch_start;
     klass->launch_finish = sev_launch_finish;
     klass->launch_update_data = sev_launch_update_data;
@@ -2242,6 +2296,7 @@ sev_snp_guest_class_init(ObjectClass *oc, void *data)
     SevCommonStateClass *klass = SEV_COMMON_CLASS(oc);
     X86ConfidentialGuestClass *x86_klass = X86_CONFIDENTIAL_GUEST_CLASS(oc);
 
+    klass->build_kernel_loader_hashes = sev_snp_build_kernel_loader_hashes;
     klass->launch_start = sev_snp_launch_start;
     klass->launch_finish = sev_snp_launch_finish;
     klass->launch_update_data = sev_snp_launch_update_data;