Re: [RFC PATCH] tee: add support for application-based session login methods

Hi Elvira,

On Thu, Sep 17, 2020 at 06:38:03PM +0300, Elvira Khabirova wrote:

GP TEE Client API in addition to login methods already supported in the kernel also defines several application-based methods: TEEC_LOGIN_APPLICATION, TEEC_LOGIN_USER_APPLICATION, and TEEC_LOGIN_GROUP_APPLICATION.

It specifies credentials generated for TEEC_LOGIN_APPLICATION as only depending on the identity of the program, being persistent within one implementation, across multiple invocations of the application and across power cycles, enabling them to be used to disambiguate persistent storage. The exact nature is REE-specific.

As the exact method of generating application identifier strings may vary between vendors, setups and installations, add two suggested methods and an exact framework for vendors to extend upon.

Signed-off-by: Elvira Khabirova e.khabirova@omprussia.ru

drivers/tee/Kconfig | 29 +++++++++ drivers/tee/tee_core.c | 136 ++++++++++++++++++++++++++++++++++++++++- 2 files changed, 164 insertions(+), 1 deletion(-)

diff --git a/drivers/tee/Kconfig b/drivers/tee/Kconfig index e99d840c2511..4cd6e0d2aad5 100644 --- a/drivers/tee/Kconfig +++ b/drivers/tee/Kconfig @@ -11,6 +11,35 @@ config TEE This implements a generic interface towards a Trusted Execution Environment (TEE). +choice

• prompt "Application ID for client UUID"
• depends on TEE
• default TEE_APPID_PATH
• help

•  This option allows to choose which method will be used to generate
  

•  application identifiers for client UUID generation when login methods
  

•  TEE_LOGIN_APPLICATION, TEE_LOGIN_USER_APPLICATION
  

•  and TEE_LOGIN_GROUP_APPLICATION are used.
  

•  Please be mindful of the security of each method in your particular
  

•  installation.
  

• config TEE_APPID_PATH

• bool "Path-based application ID"
  

• help
  

•   Use the executable's path as an application ID.
  

• config TEE_APPID_SECURITY

• bool "Security extended attribute based application ID"
  

• help
  

•   Use the executable's security extended attribute as an application ID.
  

+endchoice

+config TEE_APPID_SECURITY_XATTR

• string "Security extended attribute to use for application ID"
• depends on TEE_APPID_SECURITY
• help

•  Attribute to be used as an application ID (with the security prefix removed).
  

if TEE menu "TEE drivers" diff --git a/drivers/tee/tee_core.c b/drivers/tee/tee_core.c index 64637e09a095..19c965dd212b 100644 --- a/drivers/tee/tee_core.c +++ b/drivers/tee/tee_core.c @@ -7,8 +7,10 @@ #include <linux/cdev.h> #include <linux/cred.h> +#include <linux/file.h> #include <linux/fs.h> #include <linux/idr.h> +#include <linux/mm.h> #include <linux/module.h> #include <linux/slab.h> #include <linux/tee_drv.h> @@ -17,11 +19,15 @@ #include <crypto/sha.h> #include "tee_private.h" +#ifdef CONFIG_TEE_APPID_SECURITY

No need for the ifdef, just inlude the file unconditionally above.

+#include <linux/security.h> +#endif

#define TEE_NUM_DEVICES 32 #define TEE_IOCTL_PARAM_SIZE(x) (sizeof(struct tee_param) * (x)) -#define TEE_UUID_NS_NAME_SIZE 128 +#define TEE_UUID_NS_NAME_SIZE PATH_MAX /*

• TEE Client UUID name space identifier (UUIDv4)

@@ -125,6 +131,67 @@ static int tee_release(struct inode *inode, struct file *filp) return 0; } +#ifdef CONFIG_TEE_APPID_SECURITY +static const char *tee_session_get_application_id(void **data)

static char *get_app_id(void) should be enough.

+{

• struct file *exe_file;
• const char *name = CONFIG_TEE_APPID_SECURITY_XATTR;
• int len;
• exe_file = get_mm_exe_file(current->mm);
• if (!exe_file)

• return ERR_PTR(-ENOENT);
  

• if (!exe_file->f_inode) {

• fput(exe_file);
  

• return ERR_PTR(-ENOENT);
  

• }

You could perhaps add a comment here on the expected properties of this data. Something along (don't know if I'm even close) "string representation of the the hash of the binary and time stamp".

• len = security_inode_getsecurity(exe_file->f_inode, name, data, true);
• if (len < 0)

• return ERR_PTR(len);
  

• fput(exe_file);
• return *data;

+} +#endif /* CONFIG_TEE_APPID_SECURITY */

+#ifdef CONFIG_TEE_APPID_PATH +static const char *tee_session_get_application_id(void **data) +{

• struct file *exe_file;
• char *path;
• *data = kzalloc(TEE_UUID_NS_NAME_SIZE, GFP_KERNEL);
• if (!*data)

• return ERR_PTR(-ENOMEM);
  

• exe_file = get_mm_exe_file(current->mm);
• if (!exe_file) {

• kfree(*data);
  

• return ERR_PTR(-ENOENT);
  

• }
• path = file_path(exe_file, *data, TEE_UUID_NS_NAME_SIZE);
• if (IS_ERR(path)) {

• kfree(*data);
  

• return path;
  

• }
• fput(exe_file);
• return path;

+} +#endif /* CONFIG_TEE_APPID_PATH */

+#if defined(CONFIG_TEE_APPID_PATH) || defined(CONFIG_TEE_APPID_SECURITY) +static void tee_session_free_application_id(void *data) +{

• kfree(data);

+}

This function isn't needed, we can call kfree() directly.

+#endif /* CONFIG_TEE_APPID_PATH || CONFIG_TEE_APPID_SECURITY */

/**

• uuid_v5() - Calculate UUIDv5
• @uuid: Resulting UUID

@@ -197,6 +264,8 @@ int tee_session_calc_client_uuid(uuid_t *uuid, u32 connection_method, gid_t ns_grp = (gid_t)-1; kgid_t grp = INVALID_GID; char *name = NULL;

• void *application_id_data = NULL;

This isn't needed

• const char *application_id = NULL;

char *app_id = NULL;

int name_len; int rc; @@ -217,6 +286,14 @@ int tee_session_calc_client_uuid(uuid_t *uuid, u32 connection_method, * For TEEC_LOGIN_GROUP: * gid=<gid> *

• * For TEEC_LOGIN_APPLICATION:
  

• * app=<application id>
  

• *
  

• * For TEEC_LOGIN_USER_APPLICATION:
  

• * uid=<uid>:app=<application id>
  

• *
  

• * For TEEC_LOGIN_GROUP_APPLICATION:
  

• * gid=<gid>:app=<application id>
  

  */

name = kzalloc(TEE_UUID_NS_NAME_SIZE, GFP_KERNEL); @@ -249,6 +326,63 @@ int tee_session_calc_client_uuid(uuid_t *uuid, u32 connection_method, } break;

• case TEE_IOCTL_LOGIN_APPLICATION:

• application_id = tee_session_get_application_id(&application_id_data);
  

• if (IS_ERR(application_id)) {
  

• 	rc = PTR_ERR(application_id);
  

• 	goto out_free_name;
  

• }
  

• name_len = snprintf(name, TEE_UUID_NS_NAME_SIZE, "app=%s",
  

• 		    application_id);
  

• tee_session_free_application_id(application_id_data);
  

• if (name_len >= TEE_UUID_NS_NAME_SIZE) {
  

• 	rc = -E2BIG;
  

• 	goto out_free_name;
  

• }
  

It looks like we remove these tests and replace them with if (name_len < TEE_UUID_NS_NAME_SIZE) rc = uuid_v5(uuid, &tee_client_uuid_ns, name, name_len); else rc = -E2BIG

below, just above the "out_free_name:" label.

This function is small and simple enough that it should be easy to see what's going on any way.

Thanks, Jens

• break;
  

• case TEE_IOCTL_LOGIN_USER_APPLICATION:

• application_id = tee_session_get_application_id(&application_id_data);
  

• if (IS_ERR(application_id)) {
  

• 	rc = PTR_ERR(application_id);
  

• 	goto out_free_name;
  

• }
  

• name_len = snprintf(name, TEE_UUID_NS_NAME_SIZE, "uid=%x:app=%s",
  

• 		    current_euid().val, application_id);
  

• tee_session_free_application_id(application_id_data);
  

• if (name_len >= TEE_UUID_NS_NAME_SIZE) {
  

• 	rc = -E2BIG;
  

• 	goto out_free_name;
  

• }
  

• break;
  

• case TEE_IOCTL_LOGIN_GROUP_APPLICATION:

• 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;
  

• }
  

• application_id = tee_session_get_application_id(&application_id_data);
  

• if (IS_ERR(application_id)) {
  

• 	rc = PTR_ERR(application_id);
  

• 	goto out_free_name;
  

• }
  

• name_len = snprintf(name, TEE_UUID_NS_NAME_SIZE, "gid=%x:app=%s",
  

• 		    grp.val, application_id);
  

• tee_session_free_application_id(application_id_data);
  

• if (name_len >= TEE_UUID_NS_NAME_SIZE) {
  

• 	rc = -E2BIG;
  

• 	goto out_free_name;
  

• }
  

• break;
  

• default: rc = -EINVAL; goto out_free_name;

-- 2.28.0