diff --git a/services/std_svc/rmmd/rmmd_attest.c b/services/std_svc/rmmd/rmmd_attest.c
index 6c5f368..355b034 100644
--- a/services/std_svc/rmmd/rmmd_attest.c
+++ b/services/std_svc/rmmd/rmmd_attest.c
@@ -56,110 +56,96 @@
 }
 
 /*
- * TODO: Have different error codes for different errors so that the caller can
- * differentiate various error cases.
+ * Helper function to validate that the buffer base and length are
+ * within range.
  */
-int rmmd_attest_get_platform_token(uint64_t buf_pa, uint64_t *buf_len, uint64_t challenge_hash_len)
+static int validate_buffer_params(uint64_t buf_pa, uint64_t buf_len)
 {
-	int err;
-	uintptr_t va;
-	uint8_t temp_buf[SHA512_DIGEST_SIZE];
+	unsigned long shared_buf_page;
+	uintptr_t shared_buf_base;
 
-	/*
-	 * 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.
-	 */
+	(void)plat_rmmd_get_el3_rmm_shared_mem(&shared_buf_base);
 
-	/* We need a page of buffer to pass data */
-	if (*buf_len != PAGE_SIZE) {
-		ERROR("Invalid buffer length\n");
-		return RMMD_ERR_INVAL;
+	shared_buf_page = shared_buf_base & ~PAGE_SIZE_MASK;
+
+	/* Validate the buffer pointer */
+	if ((buf_pa & ~PAGE_SIZE_MASK) != shared_buf_page) {
+		ERROR("Buffer PA out of range\n");
+		return E_RMM_BAD_ADDR;
 	}
 
-	if ((challenge_hash_len != SHA256_DIGEST_SIZE) &&
-	    (challenge_hash_len != SHA384_DIGEST_SIZE) &&
-	    (challenge_hash_len != SHA512_DIGEST_SIZE)) {
-		ERROR("Invalid hash size: %lu\n", challenge_hash_len);
-		return RMMD_ERR_INVAL;
+	/* Validate the size of the shared area */
+	if (((buf_pa + buf_len - 1UL) & ~PAGE_SIZE_MASK) != shared_buf_page) {
+		ERROR("Invalid buffer length\n");
+		return E_RMM_INVAL;
 	}
 
-	spin_lock(&lock);
+	return 0; /* No error */
+}
+
+int rmmd_attest_get_platform_token(uint64_t buf_pa, uint64_t *buf_size,
+				   uint64_t c_size)
+{
+	int err;
+	uint8_t temp_buf[SHA512_DIGEST_SIZE];
 
-	/* 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);
+	err = validate_buffer_params(buf_pa, *buf_size);
 	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;
+		return err;
 	}
 
-	(void)memcpy(temp_buf, (void *)va, challenge_hash_len);
+	if ((c_size != SHA256_DIGEST_SIZE) &&
+	    (c_size != SHA384_DIGEST_SIZE) &&
+	    (c_size != SHA512_DIGEST_SIZE)) {
+		ERROR("Invalid hash size: %lu\n", c_size);
+		return E_RMM_INVAL;
+	}
+
+	spin_lock(&lock);
 
-	print_challenge((uint8_t *)temp_buf, challenge_hash_len);
+	(void)memcpy(temp_buf, (void *)buf_pa, c_size);
+
+	print_challenge((uint8_t *)temp_buf, c_size);
 
 	/* Get the platform token. */
-	err = plat_rmmd_get_cca_attest_token(va,
-		buf_len, (uintptr_t)temp_buf, challenge_hash_len);
+	err = plat_rmmd_get_cca_attest_token((uintptr_t)buf_pa,
+		buf_size, (uintptr_t)temp_buf, c_size);
 
 	if (err != 0) {
 		ERROR("Failed to get platform token: %d.\n", err);
-		err = RMMD_ERR_UNK;
+		err = E_RMM_UNK;
 	}
 
-	/* Unmap RMM memory. */
-	(void)mmap_remove_dynamic_region(va, PAGE_SIZE);
 	spin_unlock(&lock);
 
 	return err;
 }
 
-int rmmd_attest_get_signing_key(uint64_t buf_pa, uint64_t *buf_len,
+int rmmd_attest_get_signing_key(uint64_t buf_pa, uint64_t *buf_size,
 				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;
+	err = validate_buffer_params(buf_pa, *buf_size);
+	if (err != 0) {
+		return err;
 	}
 
 	if (ecc_curve != ATTEST_KEY_CURVE_ECC_SECP384R1) {
 		ERROR("Invalid ECC curve specified\n");
-		return RMMD_ERR_INVAL;
+		return E_RMM_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_rmmd_get_cca_realm_attest_key(va, buf_len, (unsigned int)ecc_curve);
+	err = plat_rmmd_get_cca_realm_attest_key((uintptr_t)buf_pa, buf_size,
+						 (unsigned int)ecc_curve);
 	if (err != 0) {
 		ERROR("Failed to get attestation key: %d.\n", err);
-		err =  RMMD_ERR_UNK;
+		err =  E_RMM_UNK;
 	}
 
-	/* Unmap RMM memory. */
-	(void)mmap_remove_dynamic_region(va, PAGE_SIZE);
 	spin_unlock(&lock);
 
 	return err;
diff --git a/services/std_svc/rmmd/rmmd_main.c b/services/std_svc/rmmd/rmmd_main.c
index d128e3e..27a1ad9 100644
--- a/services/std_svc/rmmd/rmmd_main.c
+++ b/services/std_svc/rmmd/rmmd_main.c
@@ -33,12 +33,6 @@
 #include "rmmd_private.h"
 
 /*******************************************************************************
- * RMM <-> EL3 shared buffer information.
- ******************************************************************************/
-static size_t shared_buf_size;
-static uintptr_t shared_buf_base;
-
-/*******************************************************************************
  * RMM boot failure flag
  ******************************************************************************/
 static bool rmm_boot_failed;
@@ -172,6 +166,8 @@
  ******************************************************************************/
 int rmmd_setup(void)
 {
+	size_t shared_buf_size __unused;
+	uintptr_t shared_buf_base;
 	uint32_t ep_attr;
 	unsigned int linear_id = plat_my_core_pos();
 	rmmd_rmm_context_t *rmm_ctx = &rmm_context[linear_id];
@@ -371,15 +367,15 @@
 	int ret;
 
 	if (error == 0) {
-		return RMMD_OK;
+		return E_RMM_OK;
 	}
 
 	if (error == -EINVAL) {
-		ret = RMMD_ERR_BAD_ADDR;
+		ret = E_RMM_BAD_ADDR;
 	} else {
 		/* This is the only other error code we expect */
 		assert(error == -EPERM);
-		ret = RMMD_ERR_BAD_PAS;
+		ret = E_RMM_BAD_PAS;
 	}
 
 	ERROR("RMMD: PAS Transition failed. GPT ret = %d, PA: 0x%"PRIx64 ", FID = 0x%x\n",
diff --git a/services/std_svc/rmmd/rmmd_private.h b/services/std_svc/rmmd/rmmd_private.h
index e964ead..4954a43 100644
--- a/services/std_svc/rmmd/rmmd_private.h
+++ b/services/std_svc/rmmd/rmmd_private.h
@@ -46,10 +46,10 @@
 __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);
+int rmmd_attest_get_platform_token(uint64_t buf_pa, uint64_t *buf_size,
+				   uint64_t c_size);
+int rmmd_attest_get_signing_key(uint64_t buf_pa, uint64_t *buf_size,
+				uint64_t ecc_curve);
 
 /* Assembly helpers */
 uint64_t rmmd_rmm_enter(uint64_t *c_rt_ctx);