[Qemu-devel] [PATCH 2/2] smbios: Encode UUID according to SMBIOS specification

[Eduardo Habkost]

Differently from older versions, SMBIOS version 2.6 is explicit about
the encoding of UUID fields:

> Although RFC 4122 recommends network byte order for all fields, the PC
> industry (including the ACPI, UEFI, and Microsoft specifications) has
> consistently used little-endian byte encoding for the first three fields:
> time_low, time_mid, time_hi_and_version. The same encoding, also known as
> wire format, should also be used for the SMBIOS representation of the UUID.
>
> The UUID {00112233-4455-6677-8899-AABBCCDDEEFF} would thus be represented
> as 33 22 11 00 55 44 77 66 88 99 AA BB CC DD EE FF.

The dmidecode tool implements this and decodes the above "wire format"
when SMBIOS version >= 2.6. We moved from SMBIOS version 2.4 to 2.8 when
we started building the SMBIOS entry point inside QEMU, on commit
c97294ec1b9e36887e119589d456557d72ab37b5.

Change smbios_build_type_1_table() to encode the UUID as specified.

To make sure we won't change the guest-visible UUID when upgrading to a
newer QEMU version, keep the old behavior on pc-*-2.1 and older.

Signed-off-by: Eduardo Habkost <address@hidden>
---
 hw/i386/pc_piix.c        |  4 +++-
 hw/i386/pc_q35.c         |  4 +++-
 hw/i386/smbios.c         | 27 ++++++++++++++++++++++++---
 include/hw/i386/smbios.h | 17 +++++++++++++++--
 vl.c                     |  3 +++
 5 files changed, 48 insertions(+), 7 deletions(-)

diff --git a/hw/i386/pc_piix.c b/hw/i386/pc_piix.c
index 162b77e..67c9ec3 100644
--- a/hw/i386/pc_piix.c
+++ b/hw/i386/pc_piix.c
@@ -63,6 +63,7 @@ static bool has_acpi_build = true;
 static int legacy_acpi_table_size;
 static bool smbios_defaults = true;
 static bool smbios_legacy_mode;
+static bool smbios_uuid_encoded = true;
 /* Make sure that guest addresses aligned at 1Gbyte boundaries get mapped to
  * host addresses aligned at 1Gbyte boundaries.  This way we can use 1GByte
  * pages in the host.
@@ -172,7 +173,7 @@ static void pc_init1(MachineState *machine,
         MachineClass *mc = MACHINE_GET_CLASS(machine);
         /* These values are guest ABI, do not change */
         smbios_set_defaults("QEMU", "Standard PC (i440FX + PIIX, 1996)",
-                            mc->name, smbios_legacy_mode);
+                            mc->name, smbios_legacy_mode, smbios_uuid_encoded);
     }
 
     /* allocate ram and load rom/bios */
@@ -304,6 +305,7 @@ static void pc_init_pci(MachineState *machine)
 
 static void pc_compat_2_1(MachineState *machine)
 {
+    smbios_uuid_encoded = false;
 }
 
 static void pc_compat_2_0(MachineState *machine)
diff --git a/hw/i386/pc_q35.c b/hw/i386/pc_q35.c
index 0490980..56db5ec 100644
--- a/hw/i386/pc_q35.c
+++ b/hw/i386/pc_q35.c
@@ -52,6 +52,7 @@
 static bool has_acpi_build = true;
 static bool smbios_defaults = true;
 static bool smbios_legacy_mode;
+static bool smbios_uuid_encoded = true;
 /* Make sure that guest addresses aligned at 1Gbyte boundaries get mapped to
  * host addresses aligned at 1Gbyte boundaries.  This way we can use 1GByte
  * pages in the host.
@@ -163,7 +164,7 @@ static void pc_q35_init(MachineState *machine)
         MachineClass *mc = MACHINE_GET_CLASS(machine);
         /* These values are guest ABI, do not change */
         smbios_set_defaults("QEMU", "Standard PC (Q35 + ICH9, 2009)",
-                            mc->name, smbios_legacy_mode);
+                            mc->name, smbios_legacy_mode, smbios_uuid_encoded);
     }
 
     /* allocate ram and load rom/bios */
@@ -282,6 +283,7 @@ static void pc_q35_init(MachineState *machine)
 
 static void pc_compat_2_1(MachineState *machine)
 {
+    smbios_uuid_encoded = false;
 }
 
 static void pc_compat_2_0(MachineState *machine)
diff --git a/hw/i386/smbios.c b/hw/i386/smbios.c
index e3fa1b2..1c99341 100644
--- a/hw/i386/smbios.c
+++ b/hw/i386/smbios.c
@@ -48,6 +48,7 @@ struct smbios_table {
 static uint8_t *smbios_entries;
 static size_t smbios_entries_len;
 static bool smbios_legacy = true;
+static bool smbios_uuid_encoded = true;
 /* end: legacy structures & constants for <= 2.0 machines */
 
 
@@ -391,6 +392,11 @@ static void smbios_build_type_1_fields(void)
     smbios_maybe_add_str(1, offsetof(struct smbios_type_1, family_str),
                          type1.family);
     if (qemu_uuid_set) {
+        /* We don't encode the UUID in the "wire format" here because this
+         * function is for legacy mode and needs to keep the guest ABI, and
+         * because we don't know what's the SMBIOS version advertised by the
+         * BIOS.
+         */
         smbios_add_field(1, offsetof(struct smbios_type_1, uuid),
                          qemu_uuid, 16);
     }
@@ -523,6 +529,19 @@ static void smbios_build_type_0_table(void)
     SMBIOS_BUILD_TABLE_POST;
 }
 
+/* Encode UUID from the big endian encoding described on RFC4122 to the wire
+ * format specified by SMBIOS version 2.6.
+ */
+static void smbios_encode_uuid(struct smbios_uuid *uuid, const uint8_t *buf)
+{
+    memcpy(uuid, buf, 16);
+    if (smbios_uuid_encoded) {
+        uuid->time_low = bswap32(uuid->time_low);
+        uuid->time_mid = bswap16(uuid->time_mid);
+        uuid->time_hi_and_version = bswap16(uuid->time_hi_and_version);
+    }
+}
+
 static void smbios_build_type_1_table(void)
 {
     SMBIOS_BUILD_TABLE_PRE(1, 0x100, true); /* required */
@@ -532,9 +551,9 @@ static void smbios_build_type_1_table(void)
     SMBIOS_TABLE_SET_STR(1, version_str, type1.version);
     SMBIOS_TABLE_SET_STR(1, serial_number_str, type1.serial);
     if (qemu_uuid_set) {
-        memcpy(t->uuid, qemu_uuid, 16);
+        smbios_encode_uuid(&t->uuid, qemu_uuid);
     } else {
-        memset(t->uuid, 0, 16);
+        memset(&t->uuid, 0, 16);
     }
     t->wake_up_type = 0x06; /* power switch */
     SMBIOS_TABLE_SET_STR(1, sku_number_str, type1.sku);
@@ -746,10 +765,12 @@ void smbios_set_cpuid(uint32_t version, uint32_t features)
     }
 
 void smbios_set_defaults(const char *manufacturer, const char *product,
-                         const char *version, bool legacy_mode)
+                         const char *version, bool legacy_mode,
+                         bool uuid_encoded)
 {
     smbios_have_defaults = true;
     smbios_legacy = legacy_mode;
+    smbios_uuid_encoded = uuid_encoded;
 
     /* drop unwanted version of command-line file blob(s) */
     if (smbios_legacy) {
diff --git a/include/hw/i386/smbios.h b/include/hw/i386/smbios.h
index a3f4d88..d2850be 100644
--- a/include/hw/i386/smbios.h
+++ b/include/hw/i386/smbios.h
@@ -20,7 +20,8 @@
 void smbios_entry_add(QemuOpts *opts);
 void smbios_set_cpuid(uint32_t version, uint32_t features);
 void smbios_set_defaults(const char *manufacturer, const char *product,
-                         const char *version, bool legacy_mode);
+                         const char *version, bool legacy_mode,
+                         bool uuid_encoded);
 uint8_t *smbios_get_table_legacy(size_t *length);
 void smbios_get_tables(uint8_t **tables, size_t *tables_len,
                        uint8_t **anchor, size_t *anchor_len);
@@ -72,6 +73,18 @@ struct smbios_type_0 {
     uint8_t embedded_controller_minor_release;
 } QEMU_PACKED;
 
+/* UUID encoding. The time_* fields are little-endian, as specified by SMBIOS
+ * version 2.6.
+ */
+struct smbios_uuid {
+    uint32_t time_low;
+    uint16_t time_mid;
+    uint16_t time_hi_and_version;
+    uint8_t clock_seq_hi_and_reserved;
+    uint8_t clock_seq_low;
+    uint8_t node[6];
+} QEMU_PACKED;
+
 /* SMBIOS type 1 - System Information */
 struct smbios_type_1 {
     struct smbios_structure_header header;
@@ -79,7 +92,7 @@ struct smbios_type_1 {
     uint8_t product_name_str;
     uint8_t version_str;
     uint8_t serial_number_str;
-    uint8_t uuid[16];
+    struct smbios_uuid uuid;
     uint8_t wake_up_type;
     uint8_t sku_number_str;
     uint8_t family_str;
diff --git a/vl.c b/vl.c
index f6b3546..1bde561 100644
--- a/vl.c
+++ b/vl.c
@@ -190,6 +190,9 @@ int nb_numa_nodes;
 int max_numa_nodeid;
 NodeInfo numa_info[MAX_NODES];
 
+/* The bytes in qemu_uuid[] are in the order specified by RFC4122, _not_ in the
+ * little-endian "wire format" described in the SMBIOS 2.6 specification.
+ */
 uint8_t qemu_uuid[16];
 bool qemu_uuid_set;
 
-- 
1.9.3