[SeaBIOS] [RFC PATCH v1 6/9] tpm: Implement tpm2_prepboot

[Stefan Berger]

From: Stefan Berger

Implement tpm2_preboot.

Here we set the platform password to a random password that prevents
higher layers (OS) to get this password. This avoids bad things like users
clearing the TPM, erasing EK (primary key) certificates, changing the
primary key etc.

The clearing of the TPM will still be possible through the TPM 2 menu.

Signed-off-by: Stefan Berger 
---
 src/std/tcg.h |  44 +++++++++++++++++++++++
 src/tcgbios.c | 110 ++++++++++++++++++++++++++++++++++++++++++++++++++++++++--
 2 files changed, 152 insertions(+), 2 deletions(-)

diff --git a/src/std/tcg.h b/src/std/tcg.h
index db1155d..e0d6f30 100644
--- a/src/std/tcg.h
+++ b/src/std/tcg.h
@@ -372,14 +372,58 @@ struct tpm_res_sha1complete {
 #define TPM2_SU_CLEAR               0x0000
 #define TPM2_SU_STATE               0x0001

+#define TPM2_RS_PW                  0x40000009
+#define TPM2_RH_PLATFORM            0x4000000c
+
 /* TPM 2 command tags */
 #define TPM2_ST_NO_SESSIONS         0x8001
+#define TPM2_ST_SESSIONS            0x8002

/* TPM 2 commands */
+#define TPM2_CC_HierarchyChangeAuth 0x129
 #define TPM2_CC_SelfTest            0x143
 #define TPM2_CC_Startup             0x144
+#define TPM2_CC_StirRandom          0x146
+#define TPM2_CC_GetRandom           0x17b

/* TPM 2 error codes */
 #define TPM2_RC_INITIALIZE          0x100

+/* TPM 2 data structures */
+
+struct tpm2b_stir {
+    u16 size;
+    u64 stir;
+} PACKED;
+
+struct tpm2_req_getrandom {
+    struct tpm_req_header hdr;
+    u16 bytesRequested;
+} PACKED;
+
+struct tpm2b_20 {
+    u16 size;
+    u8 buffer[20];
+} PACKED;
+
+struct tpm2_res_getrandom {
+    struct tpm_rsp_header hdr;
+    struct tpm2b_20 rnd;
+} PACKED;
+
+struct tpm2_authblock {
+    u32 handle;
+    u16 noncesize;  /* always 0 */
+    u8 contsession; /* always TPM2_YES */
+    u16 pwdsize;    /* always 0 */
+} PACKED;
+
+struct tpm2_req_hierarchychangeauth {
+    struct tpm_req_header hdr;
+    u32 authhandle;
+    u32 authblocksize;
+    struct tpm2_authblock authblock;
+    struct tpm2b_20 newAuth;
+} PACKED;
+
 #endif // tcg.h
diff --git a/src/tcgbios.c b/src/tcgbios.c
index 7b6409c..4f5c5bb 100644
--- a/src/tcgbios.c
+++ b/src/tcgbios.c
@@ -204,7 +204,7 @@ tpm_build_and_send_cmd(u8 locty, u32 ordinal, const u8 *append,
 {
     struct {
         struct tpm_req_header trqh;
-        u8 cmd[6];
+        u8 cmd[10];
     } PACKED req = {
         .trqh.tag = cpu_to_be16(TPM_TAG_RQU_CMD),
         .trqh.totlen = cpu_to_be32(sizeof(req.trqh) + append_size),
@@ -654,6 +654,112 @@ tpm_setup(void)
     tpm_add_action(2, "Start Option ROM Scan");
 }

+static int
+tpm2_stirrandom(void)
+{
+    struct tpm2b_stir stir = {
+        .size = cpu_to_be16(sizeof(stir.stir)),
+        .stir = rdtscll(),
+    };
+    /* set more bits to stir with */
+    stir.stir += swab64(rdtscll());
+
+    return tpm_build_and_send_cmd(0, TPM2_CC_StirRandom,
+                                  (u8 *)&stir, sizeof(stir),
+                                  TPM_DURATION_TYPE_SHORT);
+}
+
+static int
+tpm2_getrandom(u8 *buf, u16 buf_len)
+{
+    struct tpm2_res_getrandom rsp;
+
+    if (buf_len > sizeof(rsp.rnd.buffer))
+        return -1;
+
+    struct tpm2_req_getrandom trgr = {
+        .hdr.tag = cpu_to_be16(TPM2_ST_NO_SESSIONS),
+        .hdr.totlen = cpu_to_be32(sizeof(trgr)),
+        .hdr.ordinal = cpu_to_be32(TPM2_CC_GetRandom),
+        .bytesRequested = cpu_to_be16(buf_len),
+    };
+    u32 resp_length = sizeof(rsp);
+
+    int ret = tpmhw_transmit(0, &trgr.hdr, &rsp, &resp_length,
+                             TPM_DURATION_TYPE_MEDIUM);
+    if (ret || resp_length != sizeof(rsp) || rsp.hdr.errcode)
+        return -1;
+
+    memcpy(buf, rsp.rnd.buffer, buf_len);
+
+    return 0;
+}
+
+static int
+tpm2_hierarchychangeauth(u8 auth[20])
+{
+    struct tpm2_req_hierarchychangeauth trhca = {
+        .hdr.tag = cpu_to_be16(TPM2_ST_SESSIONS),
+        .hdr.totlen = cpu_to_be32(sizeof(trhca)),
+        .hdr.ordinal = cpu_to_be32(TPM2_CC_HierarchyChangeAuth),
+        .authhandle = cpu_to_be32(TPM2_RH_PLATFORM),
+        .authblocksize = cpu_to_be32(sizeof(trhca.authblock)),
+        .authblock = {
+            .handle = cpu_to_be32(TPM2_RS_PW),
+            .noncesize = cpu_to_be16(0),
+            .contsession = TPM2_YES,
+            .pwdsize = cpu_to_be16(0),
+        },
+        .newAuth = {
+            .size = cpu_to_be16(sizeof(trhca.newAuth.buffer)),
+        },
+    };
+    memcpy(trhca.newAuth.buffer, auth, sizeof(trhca.newAuth.buffer));
+
+    struct tpm_rsp_header rsp;
+    u32 resp_length = sizeof(rsp);
+    int ret = tpmhw_transmit(0, &trhca.hdr, &rsp, &resp_length,
+                             TPM_DURATION_TYPE_MEDIUM);
+    if (ret || resp_length != sizeof(rsp) || rsp.errcode)
+        return -1;
+
+    return 0;
+}
+
+static void
+tpm2_prepboot(void)
+{
+    int ret = tpm2_stirrandom();
+
+    dprintf(DEBUG_tcg, "TCGBIOS: Return value from sending TPM2_StirRandom = 0x%08x\n",
+            ret);
+    if (ret)
+         goto err_exit;
+
+    u8 auth[20];
+    ret = tpm2_getrandom(&auth[0], sizeof(auth));
+
+    dprintf(DEBUG_tcg, "TCGBIOS: Return value from sending TPM2_GetRandom = 0x%08x\n",
+            ret);
+
+    if (ret)
+        goto err_exit;
+
+    ret = tpm2_hierarchychangeauth(auth);
+    dprintf(DEBUG_tcg, "TCGBIOS: Return value from sending TPM2_HierarchyChangeAuth = 0x%08x\n",
+            ret);
+
+    if (ret)
+        goto err_exit;
+
+    return;
+
+err_exit:
+    dprintf(DEBUG_tcg, "TCGBIOS: TPM malfunctioning (line %d).\n", __LINE__);
+
+    tpm_set_failure();
+}
+
 void
 tpm_prepboot(void)
 {
@@ -669,7 +775,7 @@ tpm_prepboot(void)
                                    TPM_DURATION_TYPE_SHORT);
         break;
     case TPM_VERSION_2:
-        // FIXME: missing code
+        tpm2_prepboot();
         break;
     }