pc: add parser for OVMF reset block

OVMF is developing a mechanism for depositing a GUIDed table just
below the known location of the reset vector.  The table goes
backwards in memory so all entries are of the form

<data>|len|<GUID>

Where <data> is arbtrary size and type, <len> is a uint16_t and
describes the entire length of the entry from the beginning of the
data to the end of the guid.

The foot of the table is of this form and <len> for this case
describes the entire size of the table.  The table foot GUID is
defined by OVMF as 96b582de-1fb2-45f7-baea-a366c55a082d and if the
table is present this GUID is just below the reset vector, 48 bytes
before the end of the firmware file.

Add a parser for the ovmf reset block which takes a copy of the block,
if the table foot guid is found, minus the footer and a function for
later traversal to return the data area of any specified GUIDs.

Signed-off-by: James Bottomley <jejb@linux.ibm.com>

Reviewed-by: Dr. David Alan Gilbert <dgilbert@redhat.com>
Message-Id: <20210204193939.16617-2-jejb@linux.ibm.com>
Signed-off-by: Paolo Bonzini <pbonzini@redhat.com>

1 files changed, 118 insertions, 4 deletions

diff --git a/hw/i386/pc_sysfw.c b/hw/i386/pc_sysfw.c
index 11172214f1..6404b5a86f 100644
--- a/hw/i386/pc_sysfw.c
+++ b/hw/i386/pc_sysfw.c
@@ -125,6 +125,113 @@ void pc_system_flash_cleanup_unused(PCMachineState *pcms)
     }
 }
 
+#define OVMF_TABLE_FOOTER_GUID "96b582de-1fb2-45f7-baea-a366c55a082d"
+
+static uint8_t *ovmf_table;
+static int ovmf_table_len;
+
+static void pc_system_parse_ovmf_flash(uint8_t *flash_ptr, size_t flash_size)
+{
+    uint8_t *ptr;
+    QemuUUID guid;
+    int tot_len;
+
+    /* should only be called once */
+    if (ovmf_table) {
+        return;
+    }
+
+    if (flash_size < TARGET_PAGE_SIZE) {
+        return;
+    }
+
+    /*
+     * if this is OVMF there will be a table footer
+     * guid 48 bytes before the end of the flash file.  If it's
+     * not found, silently abort the flash parsing.
+     */
+    qemu_uuid_parse(OVMF_TABLE_FOOTER_GUID, &guid);
+    guid = qemu_uuid_bswap(guid); /* guids are LE */
+    ptr = flash_ptr + flash_size - 48;
+    if (!qemu_uuid_is_equal((QemuUUID *)ptr, &guid)) {
+        return;
+    }
+
+    /* if found, just before is two byte table length */
+    ptr -= sizeof(uint16_t);
+    tot_len = le16_to_cpu(*(uint16_t *)ptr) - sizeof(guid) - sizeof(uint16_t);
+
+    if (tot_len <= 0) {
+        return;
+    }
+
+    ovmf_table = g_malloc(tot_len);
+    ovmf_table_len = tot_len;
+
+    /*
+     * ptr is the foot of the table, so copy it all to the newly
+     * allocated ovmf_table and then set the ovmf_table pointer
+     * to the table foot
+     */
+    memcpy(ovmf_table, ptr - tot_len, tot_len);
+    ovmf_table += tot_len;
+}
+
+bool pc_system_ovmf_table_find(const char *entry, uint8_t **data,
+                               int *data_len)
+{
+    uint8_t *ptr = ovmf_table;
+    int tot_len = ovmf_table_len;
+    QemuUUID entry_guid;
+
+    if (qemu_uuid_parse(entry, &entry_guid) < 0) {
+        return false;
+    }
+
+    if (!ptr) {
+        return false;
+    }
+
+    entry_guid = qemu_uuid_bswap(entry_guid); /* guids are LE */
+    while (tot_len >= sizeof(QemuUUID) + sizeof(uint16_t)) {
+        int len;
+        QemuUUID *guid;
+
+        /*
+         * The data structure is
+         *   arbitrary length data
+         *   2 byte length of entire entry
+         *   16 byte guid
+         */
+        guid = (QemuUUID *)(ptr - sizeof(QemuUUID));
+        len = le16_to_cpu(*(uint16_t *)(ptr - sizeof(QemuUUID) -
+                                        sizeof(uint16_t)));
+
+        /*
+         * just in case the table is corrupt, wouldn't want to spin in
+         * the zero case
+         */
+        if (len < sizeof(QemuUUID) + sizeof(uint16_t)) {
+            return false;
+        } else if (len > tot_len) {
+            return false;
+        }
+
+        ptr -= len;
+        tot_len -= len;
+        if (qemu_uuid_is_equal(guid, &entry_guid)) {
+            if (data) {
+                *data = ptr;
+            }
+            if (data_len) {
+                *data_len = len - sizeof(QemuUUID) - sizeof(uint16_t);
+            }
+            return true;
+        }
+    }
+    return false;
+}
+
 /*
  * Map the pcms->flash[] from 4GiB downward, and realize.
  * Map them in descending order, i.e. pcms->flash[0] at the top,
@@ -192,10 +299,17 @@ static void pc_system_flash_map(PCMachineState *pcms,
             flash_mem = pflash_cfi01_get_memory(system_flash);
             pc_isa_bios_init(rom_memory, flash_mem, size);
 
-            /* Encrypt the pflash boot ROM, if necessary */
-            flash_ptr = memory_region_get_ram_ptr(flash_mem);
-            flash_size = memory_region_size(flash_mem);
-            sev_encrypt_flash(flash_ptr, flash_size, &error_fatal);
+            /* Encrypt the pflash boot ROM */
+            if (sev_enabled()) {
+                flash_ptr = memory_region_get_ram_ptr(flash_mem);
+                flash_size = memory_region_size(flash_mem);
+                /*
+                 * OVMF places a GUIDed structures in the flash, so
+                 * search for them
+                 */
+                pc_system_parse_ovmf_flash(flash_ptr, flash_size);
+                sev_encrypt_flash(flash_ptr, flash_size, &error_fatal);
+            }
         }
     }
 }