[SeaBIOS] [PATCH v3 2/2] tcgbios: Implement TPM 2.0 menu item to activate and deactivate PCR banks

Stefan Berger posted 2 patches 5 years, 3 months ago
[SeaBIOS] [PATCH v3 2/2] tcgbios: Implement TPM 2.0 menu item to activate and deactivate PCR banks
Posted by Stefan Berger 5 years, 3 months ago
Implement a TPM 2.0 menu item that allows a user to toggle the activation
of PCR banks of the TPM 2.0. After successful activation we shut down the
TPM 2.0 and reset the machine.

Background:

A TPM 2.0 may have multiple PCR banks, such as for SHA1, SHA256, SHA384,
SHA512, and SM3-256. One or multiple of those banks may be active (by
factory for example) and modifying the set of active PCR banks is only
possible while in the firmware since it requires platform authorization.
Platform authorization is not possible for a user when in the OS since
the firmware generates a random password for the platform authorization
before booting the system and it throws that password away.

Signed-off-by: Stefan Berger <stefanb@linux.ibm.com>
---
 src/std/tcg.h |  17 ++++
 src/tcgbios.c | 223 ++++++++++++++++++++++++++++++++++++++++++++++++++
 2 files changed, 240 insertions(+)

diff --git a/src/std/tcg.h b/src/std/tcg.h
index 09a92d8..1cc1c92 100644
--- a/src/std/tcg.h
+++ b/src/std/tcg.h
@@ -336,6 +336,12 @@ struct tpm_res_sha1complete {
 #define TPM2_ALG_SHA512             0x000d
 #define TPM2_ALG_SM3_256            0x0012
 
+#define TPM2_ALG_SHA1_FLAG          (1 << 0)
+#define TPM2_ALG_SHA256_FLAG        (1 << 1)
+#define TPM2_ALG_SHA384_FLAG        (1 << 2)
+#define TPM2_ALG_SHA512_FLAG        (1 << 3)
+#define TPM2_ALG_SM3_256_FLAG       (1 << 4)
+
 /* TPM 2 command tags */
 #define TPM2_ST_NO_SESSIONS         0x8001
 #define TPM2_ST_SESSIONS            0x8002
@@ -345,8 +351,10 @@ struct tpm_res_sha1complete {
 #define TPM2_CC_Clear               0x126
 #define TPM2_CC_ClearControl        0x127
 #define TPM2_CC_HierarchyChangeAuth 0x129
+#define TPM2_CC_PCR_Allocate        0x12b
 #define TPM2_CC_SelfTest            0x143
 #define TPM2_CC_Startup             0x144
+#define TPM2_CC_Shutdown            0x145
 #define TPM2_CC_StirRandom          0x146
 #define TPM2_CC_GetCapability       0x17a
 #define TPM2_CC_GetRandom           0x17b
@@ -442,6 +450,15 @@ struct tpm2_res_getcapability {
     u8 data[0]; /* capability dependent data */
 } PACKED;
 
+struct tpm2_req_pcr_allocate {
+    struct tpm_req_header hdr;
+    u32 authhandle;
+    u32 authblocksize;
+    struct tpm2_authblock authblock;
+    u32 count;
+    u8 tpms_pcr_selections[4];
+} PACKED;
+
 struct tpms_pcr_selection {
     u16 hashAlg;
     u8 sizeOfSelect;
diff --git a/src/tcgbios.c b/src/tcgbios.c
index 0eabc60..2e503f9 100644
--- a/src/tcgbios.c
+++ b/src/tcgbios.c
@@ -163,23 +163,35 @@ struct tpm_log_entry {
 
 static const struct hash_parameters {
     u16 hashalg;
+    u8  hashalg_flag;
     u8  hash_buffersize;
+    const char *name;
 } hash_parameters[] = {
     {
         .hashalg = TPM2_ALG_SHA1,
+        .hashalg_flag = TPM2_ALG_SHA1_FLAG,
         .hash_buffersize = SHA1_BUFSIZE,
+        .name = "SHA1",
     }, {
         .hashalg = TPM2_ALG_SHA256,
+        .hashalg_flag = TPM2_ALG_SHA256_FLAG,
         .hash_buffersize = SHA256_BUFSIZE,
+        .name = "SHA256",
     }, {
         .hashalg = TPM2_ALG_SHA384,
+        .hashalg_flag = TPM2_ALG_SHA384_FLAG,
         .hash_buffersize = SHA384_BUFSIZE,
+        .name = "SHA384",
     }, {
         .hashalg = TPM2_ALG_SHA512,
+        .hashalg_flag = TPM2_ALG_SHA512_FLAG,
         .hash_buffersize = SHA512_BUFSIZE,
+        .name = "SHA512",
     }, {
         .hashalg = TPM2_ALG_SM3_256,
+        .hashalg_flag = TPM2_ALG_SM3_256_FLAG,
         .hash_buffersize = SM3_256_BUFSIZE,
+        .name = "SM3-256",
     }
 };
 
@@ -195,6 +207,42 @@ tpm20_get_hash_buffersize(u16 hashAlg)
     return -1;
 }
 
+static u8
+tpm20_hashalg_to_flag(u16 hashAlg)
+{
+    unsigned i;
+
+    for (i = 0; i < ARRAY_SIZE(hash_parameters); i++) {
+        if (hash_parameters[i].hashalg == hashAlg)
+            return hash_parameters[i].hashalg_flag;
+    }
+    return 0;
+}
+
+static u16
+tpm20_hashalg_flag_to_hashalg(u8 hashalg_flag)
+{
+    unsigned i;
+
+    for (i = 0; i < ARRAY_SIZE(hash_parameters); i++) {
+        if (hash_parameters[i].hashalg_flag == hashalg_flag)
+            return hash_parameters[i].hashalg;
+    }
+    return 0;
+}
+
+static const char *
+tpm20_hashalg_flag_to_name(u8 hashalg_flag)
+{
+    unsigned i;
+
+    for (i = 0; i < ARRAY_SIZE(hash_parameters); i++) {
+        if (hash_parameters[i].hashalg_flag == hashalg_flag)
+            return hash_parameters[i].name;
+    }
+    return NULL;
+}
+
 // Add an entry at the start of the log describing digest formats
 static int
 tpm20_write_EfiSpecIdEventStruct(void)
@@ -447,6 +495,115 @@ tpm20_get_pcrbanks(void)
     return ret;
 }
 
+static int
+tpm20_get_suppt_pcrbanks(u8 *suppt_pcrbanks, u8 *active_pcrbanks)
+{
+    *suppt_pcrbanks = 0;
+    *active_pcrbanks = 0;
+
+    if (!tpm20_pcr_selection)
+        return -1;
+
+    struct tpms_pcr_selection *sel = tpm20_pcr_selection->selections;
+    void *end = (void*)tpm20_pcr_selection + tpm20_pcr_selection_size;
+
+    while (1) {
+        u8 sizeOfSelect = sel->sizeOfSelect;
+        void *nsel = (void*)sel + sizeof(*sel) + sizeOfSelect;
+        if (nsel > end)
+            return 0;
+
+        u16 hashalg = be16_to_cpu(sel->hashAlg);
+        u8 hashalg_flag = tpm20_hashalg_to_flag(hashalg);
+
+        *suppt_pcrbanks |= hashalg_flag;
+
+        unsigned i;
+        for (i = 0; i < sizeOfSelect; i++) {
+            if (sel->pcrSelect[i]) {
+                *active_pcrbanks |= hashalg_flag;
+                break;
+            }
+        }
+
+        sel = nsel;
+    }
+}
+
+static int
+tpm20_set_pcrbanks(u32 active_banks)
+{
+    struct tpm2_req_pcr_allocate trpa = {
+        .hdr.tag     = cpu_to_be16(TPM2_ST_SESSIONS),
+        .hdr.ordinal = cpu_to_be32(TPM2_CC_PCR_Allocate),
+        .authhandle = cpu_to_be32(TPM2_RH_PLATFORM),
+        .authblocksize = cpu_to_be32(sizeof(trpa.authblock)),
+        .authblock = {
+            .handle = cpu_to_be32(TPM2_RS_PW),
+            .noncesize = cpu_to_be16(0),
+            .contsession = TPM2_YES,
+            .pwdsize = cpu_to_be16(0),
+        },
+    };
+    struct tpms_pcr_selection3 {
+        u16 hashAlg;
+        u8 sizeOfSelect;
+        u8 pcrSelect[3];
+    } tps[ARRAY_SIZE(trpa.tpms_pcr_selections)];
+    int i = 0;
+    u8 hashalg_flag = TPM2_ALG_SHA1_FLAG;
+    u8 dontcare, suppt_banks;
+
+    tpm20_get_suppt_pcrbanks(&suppt_banks, &dontcare);
+
+    while (hashalg_flag) {
+        if ((hashalg_flag & suppt_banks)) {
+            u16 hashalg = tpm20_hashalg_flag_to_hashalg(hashalg_flag);
+
+            if (hashalg) {
+                u8 mask = 0;
+                tps[i].hashAlg = cpu_to_be16(hashalg);
+                tps[i].sizeOfSelect = 3;
+
+                if (active_banks & hashalg_flag)
+                    mask = 0xff;
+
+                tps[i].pcrSelect[0] = mask;
+                tps[i].pcrSelect[1] = mask;
+                tps[i].pcrSelect[2] = mask;
+                i++;
+            }
+        }
+        hashalg_flag <<= 1;
+    }
+
+    trpa.count = cpu_to_be32(i);
+    memcpy(trpa.tpms_pcr_selections, tps, i * sizeof(tps[0]));
+    trpa.hdr.totlen = cpu_to_be32(offsetof(struct tpm2_req_pcr_allocate,
+                                           tpms_pcr_selections) +
+                                  i * sizeof(tps[0]));
+
+    struct tpm_rsp_header rsp;
+    u32 resp_length = sizeof(rsp);
+
+    int ret = tpmhw_transmit(0, &trpa.hdr, &rsp, &resp_length,
+                             TPM_DURATION_TYPE_SHORT);
+    ret = ret ? -1 : be32_to_cpu(rsp.errcode);
+
+    return ret;
+}
+
+static int tpm20_activate_pcrbanks(u32 active_banks)
+{
+    int ret = tpm20_set_pcrbanks(active_banks);
+    if (!ret)
+        ret = tpm_simple_cmd(0, TPM2_CC_Shutdown,
+                             2, TPM2_SU_CLEAR, TPM_DURATION_TYPE_SHORT);
+    if (!ret)
+        reset();
+    return ret;
+}
+
 static int
 tpm12_get_capability(u32 cap, u32 subcap, struct tpm_rsp_header *rsp, u32 rsize)
 {
@@ -1962,6 +2119,68 @@ tpm12_menu(void)
     }
 }
 
+static int
+tpm20_menu_change_active_pcrbanks(void)
+{
+    u8 active_banks, suppt_banks;
+
+    tpm20_get_suppt_pcrbanks(&suppt_banks, &active_banks);
+
+    u8 activate_banks = active_banks;
+
+    while (1) {
+        u8 hashalg_flag = TPM2_ALG_SHA1_FLAG;
+        u8 i = 0;
+
+        printf("\nToggle active PCR banks by pressing number key\n\n");
+
+        while (hashalg_flag) {
+            u8 flag = hashalg_flag & suppt_banks;
+            const char *hashname = tpm20_hashalg_flag_to_name(flag);
+
+            i++;
+            if (hashname) {
+                printf("  %d: %s", i, hashname);
+                if (activate_banks & hashalg_flag)
+                    printf(" (enabled)");
+                printf("\n");
+            }
+
+            hashalg_flag <<= 1;
+        }
+        printf("\n"
+               "ESC: return to previous menu without changes\n");
+        if (activate_banks)
+            printf("A  : activate selection\n");
+
+        u8 flagnum;
+        int show = 0;
+        while (!show) {
+            int scancode = get_keystroke(1000);
+
+            switch (scancode) {
+            case ~0:
+                continue;
+            case 1: /* ESC */
+                printf("\n");
+                return -1;
+            case 2 ... 6: /* keys 1 .. 5 */
+                flagnum = scancode - 1;
+                if (flagnum > i)
+                    continue;
+                if (suppt_banks & (1 << (flagnum - 1))) {
+                    activate_banks ^= 1 << (flagnum - 1);
+                    show = 1;
+                }
+                break;
+            case 30: /* a */
+                if (activate_banks)
+                    tpm20_activate_pcrbanks(activate_banks);
+            }
+        }
+    }
+}
+
 static void
 tpm20_menu(void)
 {
@@ -1970,6 +2189,7 @@ tpm20_menu(void)
 
     for (;;) {
         printf("1. Clear TPM\n");
+        printf("2. Change active PCR banks\n");
 
         printf("\nIf no change is desired or if this menu was reached by "
                "mistake, press ESC to\n"
@@ -1988,6 +2208,9 @@ tpm20_menu(void)
         case 2:
             msgCode = TPM_PPI_OP_CLEAR;
             break;
+        case 3:
+            tpm20_menu_change_active_pcrbanks();
+            continue;
         default:
             continue;
         }
-- 
2.17.2
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