feat(rme): add dummy realm attestation key to RMMD

Add a dummy realm attestation key to RMMD, and return it on request.
The realm attestation key is requested with an SMC with the following
parameters:
    * Fid (0xC400001B2).
    * Attestation key buffer PA (the realm attestation key is copied
      at this address by the monitor).
    * Attestation key buffer length as input and size of realm
      attesation key as output.
    * Type of elliptic curve.

Signed-off-by: Tamas Ban <tamas.ban@arm.com>
Signed-off-by: Subhasish Ghosh <subhasish.ghosh@arm.com>
Signed-off-by: Soby Mathew <soby.mathew@arm.com>
Change-Id: I12d8d98fd221f4638ef225c9383374ddf6e65eac

docs/getting_started/porting-guide.rst

@@ -2043,6 +2043,32 @@ The parameters of the function are:
 
 The function returns 0 on success, -EINVAL on failure.
 
+Function : plat_get_cca_realm_attest_key() [mandatory when ENABLE_RME == 1]
+~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~
+
+::
+
+    Argument : uintptr_t, size_t *, unsigned int
+    Return   : int
+
+This function returns the delegated realm attestation key which will be used to
+sign Realm attestation token. The API currently only supports P-384 ECC curve
+key.
+
+The parameters of the function are:
+
+    arg0 - A pointer to the buffer where the attestation key should be copied
+           by this function. The buffer must be big enough to hold the
+           attestation key.
+
+    arg1 - Contains the size (in bytes) of the buffer passed in arg0. The
+           function returns the attestation key length in this parameter.
+
+    arg2 - The type of the elliptic curve to which the requested attestation key
+           belongs.
+
+The function returns 0 on success, -EINVAL on failure.
+
 Function : bl31_plat_enable_mmu [optional]
 ~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~
 
@@ -3180,7 +3206,7 @@ amount of open resources per driver.
 
 --------------
 
-*Copyright (c) 2013-2021, Arm Limited and Contributors. All rights reserved.*
+*Copyright (c) 2013-2022, Arm Limited and Contributors. All rights reserved.*
 
 .. _PSCI: http://infocenter.arm.com/help/topic/com.arm.doc.den0022c/DEN0022C_Power_State_Coordination_Interface.pdf
 .. _Arm Generic Interrupt Controller version 2.0 (GICv2): http://infocenter.arm.com/help/topic/com.arm.doc.ihi0048b/index.html

include/plat/common/platform.h

@@ -307,6 +307,9 @@ plat_local_state_t plat_get_target_pwr_state(unsigned int lvl,
  ******************************************************************************/
 int plat_get_cca_attest_token(uintptr_t buf, size_t *len,
 			       uintptr_t hash, size_t hash_size);
+int plat_get_cca_realm_attest_key(uintptr_t buf, size_t *len,
+				   unsigned int type);
+
 /*******************************************************************************
  * Optional BL31 functions (may be overridden)
  ******************************************************************************/

include/services/rmmd_svc.h

@@ -97,6 +97,25 @@
 #define SHA384_DIGEST_SIZE	48U
 #define SHA512_DIGEST_SIZE	64U
 
+/*
+ * Retrieve Realm attestation key from EL3. Only P-384 ECC curve key is
+ * supported. The arguments to this SMC are :
+ *    arg0 - Function ID.
+ *    arg1 - Realm attestation key buffer Physical address.
+ *    arg2 - Realm attestation key buffer size (in bytes).
+ *    arg3 - The type of the elliptic curve to which the requested
+ *           attestation key belongs to. The value should be one of the
+ *           defined curve types.
+ * The return arguments are :
+ *    ret0 - Status / error.
+ *    ret1 - Size of the realm attestation key if successful.
+ */
+#define RMMD_ATTEST_GET_REALM_KEY	RMM_FID(SMC_64, ATTEST_GET_REALM_KEY)
+
+/* ECC Curve types for attest key generation */
+#define ATTEST_KEY_CURVE_ECC_SECP384R1		0
+
+
 #ifndef __ASSEMBLER__
 #include <stdint.h>
 
@@ -120,5 +139,4 @@ uint64_t rmmd_rmm_el3_handler(uint32_t smc_fid,
 		uint64_t flags);
 
 #endif /* __ASSEMBLER__ */
-
 #endif /* RMMD_SVC_H */

plat/arm/board/fvp/fvp_realm_attest_key.c

@@ -0,0 +1,35 @@
+/*
+ * Copyright (c) 2022, ARM Limited and Contributors. All rights reserved.
+ *
+ * SPDX-License-Identifier: BSD-3-Clause
+ */
+
+#include <assert.h>
+#include <errno.h>
+#include <stddef.h>
+#include <stdint.h>
+#include <string.h>
+#include <services/rmmd_svc.h>
+
+static uint8_t sample_attest_priv_key[] = {
+	0x20, 0x11, 0xC7, 0xF0, 0x3C, 0xEE, 0x43, 0x25, 0x17, 0x6E,
+	0x52, 0x4F, 0x03, 0x3C, 0x0C, 0xE1, 0xE2, 0x1A, 0x76, 0xE6,
+	0xC1, 0xA4, 0xF0, 0xB8, 0x39, 0xAA, 0x1D, 0xF6, 0x1E, 0x0E,
+	0x8A, 0x5C, 0x8A, 0x05, 0x74, 0x0F, 0x9B, 0x69, 0xEF, 0xA7,
+	0xEB, 0x1A, 0x41, 0x85, 0xBD, 0x11, 0x7F, 0x68
+};
+
+int plat_get_cca_realm_attest_key(uintptr_t buf, size_t *len, unsigned int type)
+{
+	assert(type == ATTEST_KEY_CURVE_ECC_SECP384R1);
+
+	if (*len < sizeof(sample_attest_priv_key)) {
+		return -EINVAL;
+	}
+
+	(void)memcpy((void *)buf, sample_attest_priv_key,
+		     sizeof(sample_attest_priv_key));
+	*len = sizeof(sample_attest_priv_key);
+
+	return 0;
+}

plat/arm/board/fvp/platform.mk

@@ -193,7 +193,8 @@ endif
 
 ifeq (${ENABLE_RME},1)
 BL2_SOURCES		+=	plat/arm/board/fvp/aarch64/fvp_helpers.S
-BL31_SOURCES		+=	plat/arm/board/fvp/fvp_plat_attest_token.c
+BL31_SOURCES		+=	plat/arm/board/fvp/fvp_plat_attest_token.c	\
+				plat/arm/board/fvp/fvp_realm_attest_key.c
 endif
 
 ifeq (${BL2_AT_EL3},1)

services/std_svc/rmmd/rmmd_attest.c

@@ -116,3 +116,51 @@ int rmmd_attest_get_platform_token(uint64_t buf_pa, uint64_t *buf_len, uint64_t
 	return err;
 }
 
+int rmmd_attest_get_signing_key(uint64_t buf_pa, uint64_t *buf_len,
+				uint64_t ecc_curve)
+{
+	int err;
+	uintptr_t va;
+
+	/*
+	 * TODO: Currently we don't validate incoming buf_pa. This is a
+	 * prototype and we will need to allocate static buffer for EL3-RMM
+	 * communication.
+	 */
+
+	/* We need a page of buffer to pass data */
+	if (*buf_len != PAGE_SIZE) {
+		ERROR("Invalid buffer length\n");
+		return RMMD_ERR_INVAL;
+	}
+
+	if (ecc_curve != ATTEST_KEY_CURVE_ECC_SECP384R1) {
+		ERROR("Invalid ECC curve specified\n");
+		return RMMD_ERR_INVAL;
+	}
+
+	spin_lock(&lock);
+
+	/* Map the buffer that was provided by the RMM. */
+	err = mmap_add_dynamic_region_alloc_va(buf_pa, &va, PAGE_SIZE,
+					       MT_RW_DATA | MT_REALM);
+	if (err != 0) {
+		ERROR("mmap_add_dynamic_region_alloc_va failed: %d (%p).\n"
+		      , err, (void *)buf_pa);
+		spin_unlock(&lock);
+		return RMMD_ERR_NOMEM;
+	}
+
+	/* Get the Realm attestation key. */
+	err = plat_get_cca_realm_attest_key(va, buf_len, (unsigned int)ecc_curve);
+	if (err != 0) {
+		ERROR("Failed to get attestation key: %d.\n", err);
+		err =  RMMD_ERR_UNK;
+	}
+
+	/* Unmap RMM memory. */
+	(void)mmap_remove_dynamic_region(va, PAGE_SIZE);
+	spin_unlock(&lock);
+
+	return err;
+}

services/std_svc/rmmd/rmmd_main.c

@@ -375,6 +375,9 @@ uint64_t rmmd_rmm_el3_handler(uint32_t smc_fid, uint64_t x1, uint64_t x2,
 	case RMMD_ATTEST_GET_PLAT_TOKEN:
 		ret = rmmd_attest_get_platform_token(x1, &x2, x3);
 		SMC_RET2(handle, ret, x2);
+	case RMMD_ATTEST_GET_REALM_KEY:
+		ret = rmmd_attest_get_signing_key(x1, &x2, x3);
+		SMC_RET2(handle, ret, x2);
 	default:
 		WARN("RMMD: Unsupported RMM-EL3 call 0x%08x\n", smc_fid);
 		SMC_RET1(handle, SMC_UNK);

services/std_svc/rmmd/rmmd_private.h

@@ -54,6 +54,8 @@ __dead2 void rmmd_rmm_sync_exit(uint64_t rc);
 /* Functions implementing attestation utilities for RMM */
 int rmmd_attest_get_platform_token(uint64_t buf_pa, uint64_t *buf_len,
 				   uint64_t challenge_hash_len);
+int rmmd_attest_get_signing_key(uint64_t buf_pa, uint64_t *buf_len,
+				   uint64_t ecc_curve);
 
 /* Assembly helpers */
 uint64_t rmmd_rmm_enter(uint64_t *c_rt_ctx);