tpm2: cache the TPM supported commands, add tpm2_supports_command()

Cache the TPM's supported commands and provide a function to check if a command
is supported.

src/shared/tpm2-util.c

@@ -196,12 +196,47 @@ static int tpm2_get_capability(
         return more == TPM2_YES;
 }
 
+#define TPMA_CC_TO_TPM2_CC(cca) (((cca) & TPMA_CC_COMMANDINDEX_MASK) >> TPMA_CC_COMMANDINDEX_SHIFT)
+
 static int tpm2_cache_capabilities(Tpm2Context *c) {
         TPMU_CAPABILITIES capability;
         int r;
 
         assert(c);
 
+        /* Cache the command capabilities. The spec isn't actually clear if commands can be added/removed
+         * while running, but that would be crazy, so let's hope it is not possbile. */
+        TPM2_CC current_cc = TPM2_CC_FIRST;
+        for (;;) {
+                r = tpm2_get_capability(
+                                c,
+                                TPM2_CAP_COMMANDS,
+                                current_cc,
+                                TPM2_MAX_CAP_CC,
+                                &capability);
+                if (r < 0)
+                        return r;
+
+                TPML_CCA commands = capability.command;
+
+                /* We should never get 0; the TPM must support some commands, and it must not set 'more' if
+                 * there are no more. */
+                assert(commands.count > 0);
+
+                if (!GREEDY_REALLOC_APPEND(
+                                c->capability_commands,
+                                c->n_capability_commands,
+                                commands.commandAttributes,
+                                commands.count))
+                        return log_oom();
+
+                if (r == 0)
+                        break;
+
+                /* Set current_cc to index after last cc the TPM provided */
+                current_cc = TPMA_CC_TO_TPM2_CC(commands.commandAttributes[commands.count - 1]) + 1;
+        }
+
         /* Cache the PCR capabilities, which are safe to cache, as the only way they can change is
          * TPM2_PCR_Allocate(), which changes the allocation after the next _TPM_Init(). If the TPM is
          * reinitialized while we are using it, all our context and sessions will be invalid, so we can
@@ -257,6 +292,29 @@ int tpm2_supports_alg(Tpm2Context *c, TPM2_ALG_ID alg) {
         return tpm2_get_capability_alg(c, alg, NULL);
 }
 
+/* Get the TPMA_CC for a TPM2_CC. Returns true if the TPM supports the command and the TPMA_CC is provided,
+ * otherwise false. */
+static bool tpm2_get_capability_command(Tpm2Context *c, TPM2_CC command, TPMA_CC *ret) {
+        assert(c);
+
+        FOREACH_ARRAY(cca, c->capability_commands, c->n_capability_commands)
+                if (TPMA_CC_TO_TPM2_CC(*cca) == command) {
+                        if (ret)
+                                *ret = *cca;
+                        return true;
+                }
+
+        log_debug("TPM does not support command 0x%04" PRIx32 ".", command);
+        if (ret)
+                *ret = 0;
+
+        return false;
+}
+
+bool tpm2_supports_command(Tpm2Context *c, TPM2_CC command) {
+        return tpm2_get_capability_command(c, command, NULL);
+}
+
 /* Returns 1 if the TPM supports the ECC curve, 0 if not, or < 0 for any error. */
 static int tpm2_supports_ecc_curve(Tpm2Context *c, TPM2_ECC_CURVE curve) {
         TPMU_CAPABILITIES capability;
@@ -420,6 +478,8 @@ static Tpm2Context *tpm2_context_free(Tpm2Context *c) {
         c->tcti_context = mfree(c->tcti_context);
         c->tcti_dl = safe_dlclose(c->tcti_dl);
 
+        c->capability_commands = mfree(c->capability_commands);
+
         return mfree(c);
 }
 

src/shared/tpm2-util.h

@@ -62,6 +62,8 @@ typedef struct {
         ESYS_CONTEXT *esys_context;
 
         /* Some selected cached capabilities of the TPM */
+        TPMA_CC *capability_commands;
+        size_t n_capability_commands;
         TPML_PCR_SELECTION capability_pcrs;
 } Tpm2Context;
 
@@ -85,6 +87,7 @@ Tpm2Handle *tpm2_handle_free(Tpm2Handle *handle);
 DEFINE_TRIVIAL_CLEANUP_FUNC(Tpm2Handle*, tpm2_handle_free);
 
 int tpm2_supports_alg(Tpm2Context *c, TPM2_ALG_ID alg);
+bool tpm2_supports_command(Tpm2Context *c, TPM2_CC command);
 
 bool tpm2_test_parms(Tpm2Context *c, TPMI_ALG_PUBLIC alg, const TPMU_PUBLIC_PARMS *parms);
 

src/test/test-tpm2.c

@@ -706,6 +706,15 @@ TEST(tpm_required_tests) {
         assert_se(tpm2_supports_alg(c, TPM2_ALG_RSA) == 1);
         assert_se(tpm2_supports_alg(c, TPM2_ALG_AES) == 1);
         assert_se(tpm2_supports_alg(c, TPM2_ALG_CFB) == 1);
+
+        /* Test invalid commands */
+        assert_se(!tpm2_supports_command(c, TPM2_CC_FIRST - 1));
+        assert_se(!tpm2_supports_command(c, TPM2_CC_LAST + 1));
+
+        /* Test valid commands */
+        assert_se(tpm2_supports_command(c, TPM2_CC_Create));
+        assert_se(tpm2_supports_command(c, TPM2_CC_CreatePrimary));
+        assert_se(tpm2_supports_command(c, TPM2_CC_Unseal));
 }
 
 #endif /* HAVE_TPM2 */