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Message-ID: <20201001094758.GA928596@jade>
Date: Thu, 1 Oct 2020 11:47:58 +0200
From: Jens Wiklander <jens.wiklander@...aro.org>
To: Elvira Khabirova <e.khabirova@...russia.ru>
Cc: op-tee@...ts.trustedfirmware.org, linux-kernel@...r.kernel.org,
k.karasev@...russia.ru, s.shtylyov@...russia.ru,
vesa.jaaskelainen@...sala.com
Subject: Re: [PATCH v2] tee: add support for application-based session login
methods
On Wed, Sep 30, 2020 at 07:56:52PM +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@...russia.ru>
> ---
> drivers/tee/Kconfig | 29 +++++++++
> drivers/tee/tee_core.c | 133 ++++++++++++++++++++++++++++++++++++++---
> 2 files changed, 154 insertions(+), 8 deletions(-)
This looks good as far as I can tell, with just one small comment below.
However, I'd like someone else to review this too.
>
> diff --git a/drivers/tee/Kconfig b/drivers/tee/Kconfig
> index 6488b66d69dd..cd8f02a3d488 100644
> --- a/drivers/tee/Kconfig
> +++ b/drivers/tee/Kconfig
> @@ -10,6 +10,35 @@ 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 67186d00a52f..31fb244b59ed 100644
> --- a/drivers/tee/tee_core.c
> +++ b/drivers/tee/tee_core.c
> @@ -16,9 +16,12 @@
>
> #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/security.h>
> #include <linux/slab.h>
> #include <linux/tee_drv.h>
> #include <linux/uaccess.h>
> @@ -31,7 +34,7 @@
>
> #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)
> @@ -136,6 +139,72 @@ static int tee_release(struct inode *inode, struct file *filp)
> return 0;
> }
>
> +#ifdef CONFIG_TEE_APPID_SECURITY
> +static const char *get_app_id(void **data)
> +{
> + 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);
> + }
> +
> + /*
> + * An identifier string for the binary. Depends on the implementation.
> + * Could be, for example, a string containing the application vendor ID,
> + * or the binary's signature, or its hash and a timestamp.
> + */
> + 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 *get_app_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 free_app_id(void *data)
> +{
> + kfree(data);
> +}
> +#endif /* CONFIG_TEE_APPID_PATH || CONFIG_TEE_APPID_SECURITY */
I don't think we need this function, we could just as well use kfree()
directly instead.
Thanks,
Jens
> +
> /**
> * uuid_v5() - Calculate UUIDv5
> * @uuid: Resulting UUID
> @@ -208,6 +277,8 @@ 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 *app_id_data = NULL;
> + const char *app_id = NULL;
> int name_len;
> int rc;
>
> @@ -228,6 +299,14 @@ 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);
> @@ -238,10 +317,6 @@ int tee_session_calc_client_uuid(uuid_t *uuid, u32 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:
> @@ -254,10 +329,49 @@ int tee_session_calc_client_uuid(uuid_t *uuid, u32 connection_method,
>
> name_len = snprintf(name, TEE_UUID_NS_NAME_SIZE, "gid=%x",
> grp.val);
> - if (name_len >= TEE_UUID_NS_NAME_SIZE) {
> - rc = -E2BIG;
> + break;
> +
> + case TEE_IOCTL_LOGIN_APPLICATION:
> + app_id = get_app_id(&app_id_data);
> + if (IS_ERR(app_id)) {
> + rc = PTR_ERR(app_id);
> + goto out_free_name;
> + }
> +
> + name_len = snprintf(name, TEE_UUID_NS_NAME_SIZE, "app=%s",
> + app_id);
> + free_app_id(app_id_data);
> + break;
> +
> + case TEE_IOCTL_LOGIN_USER_APPLICATION:
> + app_id = get_app_id(&app_id_data);
> + if (IS_ERR(app_id)) {
> + rc = PTR_ERR(app_id);
> + goto out_free_name;
> + }
> +
> + name_len = snprintf(name, TEE_UUID_NS_NAME_SIZE, "uid=%x:app=%s",
> + current_euid().val, app_id);
> + free_app_id(app_id_data);
> + 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;
> + }
> +
> + app_id = get_app_id(&app_id_data);
> + if (IS_ERR(app_id)) {
> + rc = PTR_ERR(app_id);
> goto out_free_name;
> }
> +
> + name_len = snprintf(name, TEE_UUID_NS_NAME_SIZE, "gid=%x:app=%s",
> + grp.val, app_id);
> + free_app_id(app_id_data);
> break;
>
> default:
> @@ -265,7 +379,10 @@ int tee_session_calc_client_uuid(uuid_t *uuid, u32 connection_method,
> goto out_free_name;
> }
>
> - rc = uuid_v5(uuid, &tee_client_uuid_ns, name, name_len);
> + if (name_len < TEE_UUID_NS_NAME_SIZE)
> + rc = uuid_v5(uuid, &tee_client_uuid_ns, name, name_len);
> + else
> + rc = -E2BIG;
> out_free_name:
> kfree(name);
>
> --
> 2.17.1
>
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