[PATCH v7 06/17] firmware: qcom: scm: add a call for deriving the software secret

[Bartosz Golaszewski <brgl@bgdev.pl>]

From: Gaurav Kashyap <quic_gaurkash@quicinc.com>

Inline storage encryption may require deriving a software secret from
storage keys added to the kernel.

For raw keys, this can be directly done in the kernel as keys are not
encrypted in memory.

However, hardware wrapped keys can only be unwrapped by the HW wrapping
entity. In case of Qualcomm's wrapped key solution, this is done by the
Hardware Key Manager (HWKM) from Trustzone.

Add a new SCM call which provides a hook to the software secret crypto
profile API provided by the block layer.

Tested-by: Neil Armstrong <neil.armstrong@linaro.org>
Signed-off-by: Gaurav Kashyap <quic_gaurkash@quicinc.com>
Reviewed-by: Dmitry Baryshkov <dmitry.baryshkov@linaro.org>
Signed-off-by: Bartosz Golaszewski <bartosz.golaszewski@linaro.org>
---
 drivers/firmware/qcom/qcom_scm.c       | 65 ++++++++++++++++++++++++++++++++++
 drivers/firmware/qcom/qcom_scm.h       |  1 +
 include/linux/firmware/qcom/qcom_scm.h |  2 ++
 3 files changed, 68 insertions(+)

diff --git a/drivers/firmware/qcom/qcom_scm.c b/drivers/firmware/qcom/qcom_scm.c
index ebb58bd63eda..de90d21c2dfa 100644
--- a/drivers/firmware/qcom/qcom_scm.c
+++ b/drivers/firmware/qcom/qcom_scm.c
@@ -1252,6 +1252,71 @@ int qcom_scm_ice_set_key(u32 index, const u8 *key, u32 key_size,
 }
 EXPORT_SYMBOL_GPL(qcom_scm_ice_set_key);
 
+/**
+ * qcom_scm_derive_sw_secret() - Derive software secret from wrapped key
+ * @wkey: the hardware wrapped key inaccessible to software
+ * @wkey_size: size of the wrapped key
+ * @sw_secret: the secret to be derived which is exactly the secret size
+ * @sw_secret_size: size of the sw_secret
+ *
+ * Derive a software secret from a hardware wrapped key for software crypto
+ * operations.
+ * For wrapped keys, the key needs to be unwrapped, in order to derive a
+ * software secret, which can be done in the hardware from a secure execution
+ * environment.
+ *
+ * For more information on sw secret, please refer to "Hardware-wrapped keys"
+ * section of Documentation/block/inline-encryption.rst.
+ *
+ * Return: 0 on success; -errno on failure.
+ */
+int qcom_scm_derive_sw_secret(const u8 *wkey, size_t wkey_size,
+			      u8 *sw_secret, size_t sw_secret_size)
+{
+	struct qcom_scm_desc desc = {
+		.svc = QCOM_SCM_SVC_ES,
+		.cmd =  QCOM_SCM_ES_DERIVE_SW_SECRET,
+		.arginfo = QCOM_SCM_ARGS(4, QCOM_SCM_RW,
+					 QCOM_SCM_VAL, QCOM_SCM_RW,
+					 QCOM_SCM_VAL),
+		.args[1] = wkey_size,
+		.args[3] = sw_secret_size,
+		.owner = ARM_SMCCC_OWNER_SIP,
+	};
+
+	int ret;
+
+	void *wkey_buf __free(qcom_tzmem) = qcom_tzmem_alloc(__scm->mempool,
+							    wkey_size,
+							    GFP_KERNEL);
+	if (!wkey_buf)
+		return -ENOMEM;
+
+	void *secret_buf __free(qcom_tzmem) = qcom_tzmem_alloc(__scm->mempool,
+							       sw_secret_size,
+							       GFP_KERNEL);
+	if (!secret_buf) {
+		ret = -ENOMEM;
+		goto out_free_wrapped;
+	}
+
+	memcpy(wkey_buf, wkey, wkey_size);
+	desc.args[0] = qcom_tzmem_to_phys(wkey_buf);
+	desc.args[2] = qcom_tzmem_to_phys(secret_buf);
+
+	ret = qcom_scm_call(__scm->dev, &desc, NULL);
+	if (!ret)
+		memcpy(sw_secret, secret_buf, sw_secret_size);
+
+	memzero_explicit(secret_buf, sw_secret_size);
+
+out_free_wrapped:
+	memzero_explicit(wkey_buf, wkey_size);
+
+	return ret;
+}
+EXPORT_SYMBOL_GPL(qcom_scm_derive_sw_secret);
+
 /**
  * qcom_scm_hdcp_available() - Check if secure environment supports HDCP.
  *
diff --git a/drivers/firmware/qcom/qcom_scm.h b/drivers/firmware/qcom/qcom_scm.h
index 685b8f59e7a6..5a98b90ece32 100644
--- a/drivers/firmware/qcom/qcom_scm.h
+++ b/drivers/firmware/qcom/qcom_scm.h
@@ -127,6 +127,7 @@ struct qcom_tzmem_pool *qcom_scm_get_tzmem_pool(void);
 #define QCOM_SCM_SVC_ES			0x10	/* Enterprise Security */
 #define QCOM_SCM_ES_INVALIDATE_ICE_KEY	0x03
 #define QCOM_SCM_ES_CONFIG_SET_ICE_KEY	0x04
+#define QCOM_SCM_ES_DERIVE_SW_SECRET	0x07
 
 #define QCOM_SCM_SVC_HDCP		0x11
 #define QCOM_SCM_HDCP_INVOKE		0x01
diff --git a/include/linux/firmware/qcom/qcom_scm.h b/include/linux/firmware/qcom/qcom_scm.h
index 9f14976399ab..0ef4415e2023 100644
--- a/include/linux/firmware/qcom/qcom_scm.h
+++ b/include/linux/firmware/qcom/qcom_scm.h
@@ -103,6 +103,8 @@ bool qcom_scm_ice_available(void);
 int qcom_scm_ice_invalidate_key(u32 index);
 int qcom_scm_ice_set_key(u32 index, const u8 *key, u32 key_size,
 			 enum qcom_scm_ice_cipher cipher, u32 data_unit_size);
+int qcom_scm_derive_sw_secret(const u8 *wkey, size_t wkey_size,
+			      u8 *sw_secret, size_t sw_secret_size);
 
 bool qcom_scm_hdcp_available(void);
 int qcom_scm_hdcp_req(struct qcom_scm_hdcp_req *req, u32 req_cnt, u32 *resp);

-- 
2.43.0