[PATCH v2 1/3] arm64: rsi: Add helpers for Arm CCA measurement register operations

[Yeoreum Yun <yeoreum.yun@arm.com>]

From: Sami Mujawar <sami.mujawar@arm.com>

Add static inline helper functions to support reading the Realm
Initial Measurement (RIM) and reading/extending the Realm
Extensible Measurement (REM) registers.

The indices of the Arm CCA measurement registers, as defined by
the Realm Management Monitor specification, are as follows:
    Index    Register
    0        RIM
    1 - 4    REM[0 - 3]

The rsi_measurement_extend() function allows extending REM[0–3]
registers with a caller-provided digest (up to 64 bytes).
Index 0 (RIM) is read-only and cannot be extended.

The rsi_measurement_read() function allows reading measurement
values from RIM (index 0) or REM[0–3] (indices 1–4). The returned
digest is expected to be 64 bytes.

Signed-off-by: Sami Mujawar <sami.mujawar@arm.com>
---
 include/linux/arm-rsi-cmds.h | 105 ++++++++++++++++++++++++++++++++++++++++++-
 1 file changed, 104 insertions(+), 1 deletion(-)

diff --git a/include/linux/arm-rsi-cmds.h b/include/linux/arm-rsi-cmds.h
index 3f7a6a833993..608343266d81 100644
--- a/include/linux/arm-rsi-cmds.h
+++ b/include/linux/arm-rsi-cmds.h
@@ -1,6 +1,6 @@
 /* SPDX-License-Identifier: GPL-2.0-only */
 /*
- * Copyright (C) 2023 ARM Ltd.
+ * Copyright (C) 2023 - 2025 ARM Ltd.
  */
 
 #ifndef __LINUX_ARM_RSI_CMDS_H_
@@ -36,6 +36,26 @@ static inline bool is_realm_world(void) { return false; }
 #define RSI_GRANULE_SHIFT		12
 #define RSI_GRANULE_SIZE		(_AC(1, UL) << RSI_GRANULE_SHIFT)
 
+/*
+ * Maximum measurement data size in bytes.
+ * According to the RMM Specification, the width of the RmmRealmMeasurement type
+ * is 512 bits.
+ */
+#define RSI_MAX_MEASUREMENT_DATA_SIZE_BYTES  64
+
+/*
+ * Indices for the Realm Initial Measurement register (RIM) and the Realm
+ * Extensible Measurement registers (REMs).
+ * According to the RMM Specification, Realm attributes of a Realm include
+ * an array of measurement values. The first entry in this array is a RIM.
+ * The remaining entries in this array are REMs.
+ */
+#define RSI_INDEX_RIM		0
+#define RSI_INDEX_REM0		1
+#define RSI_INDEX_REM1		2
+#define RSI_INDEX_REM2		3
+#define RSI_INDEX_REM3		4
+
 enum ripas {
 	RSI_RIPAS_EMPTY = 0,
 	RSI_RIPAS_RAM = 1,
@@ -236,4 +256,87 @@ static inline unsigned long rsi_attestation_token_continue(phys_addr_t granule,
 	return res.a0;
 }
 
+/**
+ * rsi_measurement_extend - Extend the measurement value to the Realm Extensible
+ * Measurement (REM).
+ *
+ * @idx:		Index of the REM register.
+ *				Where:
+ *				Index	Register
+ *				1 - 4	REM[0-3]
+ * @digest:		The digest data to be extended.
+ * @digest_size:	Size of the digest data in bytes.
+ *
+ * Returns:
+ *  On success, returns RSI_SUCCESS.
+ *  Otherwise, -EINVAL
+ */
+static inline unsigned long rsi_measurement_extend(u32 idx,
+						   const u8 *digest,
+						   unsigned long digest_size)
+{
+	struct arm_smccc_1_2_regs regs = { 0 };
+
+	/*
+	 * Index 0 is for RIM (which is Read Only), while
+	 * REM[0-3] are indexed from 1 - 4.
+	 * The digest size can be at the most 64 bytes.
+	 */
+	if (!digest || idx < RSI_INDEX_REM0 || idx > RSI_INDEX_REM3 ||
+	    digest_size == 0 || digest_size > RSI_MAX_MEASUREMENT_DATA_SIZE_BYTES)
+		return -EINVAL;
+
+	regs.a0 = SMC_RSI_MEASUREMENT_EXTEND;
+	regs.a1 = idx;
+	regs.a2 = digest_size;
+	memcpy(&regs.a3, digest, digest_size);
+	arm_smccc_1_2_smc(&regs, &regs);
+
+	if (regs.a0 != RSI_SUCCESS)
+		return -EINVAL;
+
+	return regs.a0;
+}
+
+/**
+ * rsi_measurement_read - Read the measurement value from the Realm Initial
+ * Measurement (RIM) or the Realm Extensible Measurement (REM) register.
+ *
+ * @idx:		Index of the RIM or REM register.
+ *				Where:
+ *				Index	Register
+ *				0	RIM
+ *				1 - 4	REM[0-3]
+ * @digest:			The digest data to be returned.
+ * @digest_size:	Size of the digest data buffer in bytes.
+ *
+ * Returns:
+ *  On success, returns RSI_SUCCESS.
+ *  Otherwise, -EINVAL
+ */
+static inline unsigned long rsi_measurement_read(u32 idx,
+						 u8 *digest,
+						 unsigned long digest_size)
+{
+	struct arm_smccc_1_2_regs regs = { 0 };
+
+	/*
+	 * The digest size can be at the most 64 bytes, if less then 64 bytes
+	 * it is zero padded.
+	 */
+	if (!digest || idx > RSI_INDEX_REM3 ||
+	    digest_size == 0 || digest_size > RSI_MAX_MEASUREMENT_DATA_SIZE_BYTES)
+		return -EINVAL;
+
+	regs.a0 = SMC_RSI_MEASUREMENT_READ;
+	regs.a1 = idx;
+	arm_smccc_1_2_smc(&regs, &regs);
+
+	if (regs.a0 != RSI_SUCCESS)
+		return -EINVAL;
+
+	memcpy(digest, &regs.a1, digest_size);
+	return regs.a0;
+}
+
 #endif /* __LINUX_ARM_RSI_CMDS_H_ */

-- 
2.43.0