tee: add support for session's client UUID generation

TEE Client API defines that from user space only information needed for
specified login operations is group identifier for group based logins.

REE kernel is expected to formulate trustworthy client UUID and pass that
to TEE environment. REE kernel is required to verify that provided group
identifier for group based logins matches calling processes group
memberships.

TEE specification only defines that the information passed from REE
environment to TEE environment is encoded into on UUID.

In order to guarantee trustworthiness of client UUID user space is not
allowed to freely pass client UUID.

UUIDv5 form is used encode variable amount of information needed for
different login types.

Signed-off-by: Vesa Jääskeläinen <vesa.jaaskelainen@vaisala.com>
[jw: remove unused variable application_id]
Signed-off-by: Jens Wiklander <jens.wiklander@linaro.org>

1 files changed, 152 insertions, 0 deletions

diff --git a/drivers/tee/tee_core.c b/drivers/tee/tee_core.c
index 6aec502c495c..9fa837224fed 100644
--- a/drivers/tee/tee_core.c
+++ b/drivers/tee/tee_core.c
@@ -6,18 +6,33 @@
 #define pr_fmt(fmt) "%s: " fmt, __func__
 
 #include <linux/cdev.h>
+#include <linux/cred.h>
 #include <linux/fs.h>
 #include <linux/idr.h>
 #include <linux/module.h>
 #include <linux/slab.h>
 #include <linux/tee_drv.h>
 #include <linux/uaccess.h>
+#include <crypto/hash.h>
+#include <crypto/sha.h>
 #include "tee_private.h"
 
 #define TEE_NUM_DEVICES	32
 
 #define TEE_IOCTL_PARAM_SIZE(x) (sizeof(struct tee_param) * (x))
 
+#define TEE_UUID_NS_NAME_SIZE	128
+
+/*
+ * TEE Client UUID name space identifier (UUIDv4)
+ *
+ * Value here is random UUID that is allocated as name space identifier for
+ * forming Client UUID's for TEE environment using UUIDv5 scheme.
+ */
+static const uuid_t tee_client_uuid_ns = UUID_INIT(0x58ac9ca0, 0x2086, 0x4683,
+						   0xa1, 0xb8, 0xec, 0x4b,
+						   0xc0, 0x8e, 0x01, 0xb6);
+
 /*
  * Unprivileged devices in the lower half range and privileged devices in
  * the upper half range.
@@ -110,6 +125,143 @@ static int tee_release(struct inode *inode, struct file *filp)
 	return 0;
 }
 
+/**
+ * uuid_v5() - Calculate UUIDv5
+ * @uuid: Resulting UUID
+ * @ns: Name space ID for UUIDv5 function
+ * @name: Name for UUIDv5 function
+ * @size: Size of name
+ *
+ * UUIDv5 is specific in RFC 4122.
+ *
+ * This implements section (for SHA-1):
+ * 4.3.  Algorithm for Creating a Name-Based UUID
+ */
+static int uuid_v5(uuid_t *uuid, const uuid_t *ns, const void *name,
+		   size_t size)
+{
+	unsigned char hash[SHA1_DIGEST_SIZE];
+	struct crypto_shash *shash = NULL;
+	struct shash_desc *desc = NULL;
+	int rc;
+
+	shash = crypto_alloc_shash("sha1", 0, 0);
+	if (IS_ERR(shash)) {
+		rc = PTR_ERR(shash);
+		pr_err("shash(sha1) allocation failed\n");
+		return rc;
+	}
+
+	desc = kzalloc(sizeof(*desc) + crypto_shash_descsize(shash),
+		       GFP_KERNEL);
+	if (!desc) {
+		rc = -ENOMEM;
+		goto out_free_shash;
+	}
+
+	desc->tfm = shash;
+
+	rc = crypto_shash_init(desc);
+	if (rc < 0)
+		goto out_free_desc;
+
+	rc = crypto_shash_update(desc, (const u8 *)ns, sizeof(*ns));
+	if (rc < 0)
+		goto out_free_desc;
+
+	rc = crypto_shash_update(desc, (const u8 *)name, size);
+	if (rc < 0)
+		goto out_free_desc;
+
+	rc = crypto_shash_final(desc, hash);
+	if (rc < 0)
+		goto out_free_desc;
+
+	memcpy(uuid->b, hash, UUID_SIZE);
+
+	/* Tag for version 5 */
+	uuid->b[6] = (hash[6] & 0x0F) | 0x50;
+	uuid->b[8] = (hash[8] & 0x3F) | 0x80;
+
+out_free_desc:
+	kfree(desc);
+
+out_free_shash:
+	crypto_free_shash(shash);
+	return rc;
+}
+
+int tee_session_calc_client_uuid(uuid_t *uuid, u32 connection_method,
+				 const u8 connection_data[TEE_IOCTL_UUID_LEN])
+{
+	gid_t ns_grp = (gid_t)-1;
+	kgid_t grp = INVALID_GID;
+	char *name = NULL;
+	int name_len;
+	int rc;
+
+	if (connection_method == TEE_IOCTL_LOGIN_PUBLIC) {
+		/* Nil UUID to be passed to TEE environment */
+		uuid_copy(uuid, &uuid_null);
+		return 0;
+	}
+
+	/*
+	 * In Linux environment client UUID is based on UUIDv5.
+	 *
+	 * Determine client UUID with following semantics for 'name':
+	 *
+	 * For TEEC_LOGIN_USER:
+	 * uid=<uid>
+	 *
+	 * For TEEC_LOGIN_GROUP:
+	 * gid=<gid>
+	 *
+	 */
+
+	name = kzalloc(TEE_UUID_NS_NAME_SIZE, GFP_KERNEL);
+	if (!name)
+		return -ENOMEM;
+
+	switch (connection_method) {
+	case TEE_IOCTL_LOGIN_USER:
+		name_len = snprintf(name, TEE_UUID_NS_NAME_SIZE, "uid=%x",
+				    current_euid().val);
+		if (name_len >= TEE_UUID_NS_NAME_SIZE) {
+			rc = -E2BIG;
+			goto out_free_name;
+		}
+		break;
+
+	case TEE_IOCTL_LOGIN_GROUP:
+		memcpy(&ns_grp, connection_data, sizeof(gid_t));
+		grp = make_kgid(current_user_ns(), ns_grp);
+		if (!gid_valid(grp) || !in_egroup_p(grp)) {
+			rc = -EPERM;
+			goto out_free_name;
+		}
+
+		name_len = snprintf(name, TEE_UUID_NS_NAME_SIZE, "gid=%x",
+				    grp.val);
+		if (name_len >= TEE_UUID_NS_NAME_SIZE) {
+			rc = -E2BIG;
+			goto out_free_name;
+		}
+		break;
+
+	default:
+		rc = -EINVAL;
+		goto out_free_name;
+	}
+
+	rc = uuid_v5(uuid, &tee_client_uuid_ns, name, name_len);
+out_free_name:
+	kfree(name);
+
+	return rc;
+}
+EXPORT_SYMBOL_GPL(tee_session_calc_client_uuid);
+
 static int tee_ioctl_version(struct tee_context *ctx,
 			     struct tee_ioctl_version_data __user *uvers)
 {