[PATCH v25 13/21] x86/sgx: Add provisioning

Jarkko Sakkinen
2020-02-04T06:07:14Z

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In order to provide a mechanism for devilering provisoning rights:

1. Add a new device file /dev/sgx/provision that works as a token for
allowing an enclave to have the provisioning privileges.
2. Add a new ioctl called SGX_IOC_ENCLAVE_SET_ATTRIBUTE that accepts the
following data structure:

struct sgx_enclave_set_attribute {
__u64 addr;
__u64 attribute_fd;
};

A daemon could sit on top of /dev/sgx/provision and send a file
descriptor of this file to a process that needs to be able to provision
enclaves.

The way this API is used is straight-forward. Lets assume that dev_fd is
a handle to /dev/sgx/enclave and prov_fd is a handle to
/dev/sgx/provision. You would allow SGX_IOC_ENCLAVE_CREATE to
initialize an enclave with the PROVISIONKEY attribute by

params.addr = <enclave address>;
params.token_fd = prov_fd;

ioctl(dev_fd, SGX_IOC_ENCLAVE_SET_ATTRIBUTE, &params);

Cc: linux-security-module@vger.kernel.org
Suggested-by: Andy Lutomirski <luto@kernel.org>
Signed-off-by: Jarkko Sakkinen <jarkko.sakkinen@linux.intel.com>
---
arch/x86/include/uapi/asm/sgx.h | 11 ++++++++
arch/x86/kernel/cpu/sgx/driver.c | 14 ++++++++++
arch/x86/kernel/cpu/sgx/driver.h | 2 ++
arch/x86/kernel/cpu/sgx/ioctl.c | 47 ++++++++++++++++++++++++++++++++
4 files changed, 74 insertions(+)

diff --git a/arch/x86/include/uapi/asm/sgx.h b/arch/x86/include/uapi/asm/sgx.h
index 5edb08ab8fd0..57d0d30c79b3 100644
--- a/arch/x86/include/uapi/asm/sgx.h
+++ b/arch/x86/include/uapi/asm/sgx.h
@@ -25,6 +25,8 @@ enum sgx_page_flags {
_IOWR(SGX_MAGIC, 0x01, struct sgx_enclave_add_pages)
#define SGX_IOC_ENCLAVE_INIT \
_IOW(SGX_MAGIC, 0x02, struct sgx_enclave_init)
+#define SGX_IOC_ENCLAVE_SET_ATTRIBUTE \
+ _IOW(SGX_MAGIC, 0x03, struct sgx_enclave_set_attribute)

/**
* struct sgx_enclave_create - parameter structure for the
@@ -63,4 +65,13 @@ struct sgx_enclave_init {
__u64 sigstruct;
};

+/**
+ * struct sgx_enclave_set_attribute - parameter structure for the
+ * %SGX_IOC_ENCLAVE_SET_ATTRIBUTE ioctl
+ * @attribute_fd: file handle of the attribute file in the securityfs
+ */
+struct sgx_enclave_set_attribute {
+ __u64 attribute_fd;
+};
+
#endif /* _UAPI_ASM_X86_SGX_H */
diff --git a/arch/x86/kernel/cpu/sgx/driver.c b/arch/x86/kernel/cpu/sgx/driver.c
index b4aa7b9f8376..d90114cec1c3 100644
--- a/arch/x86/kernel/cpu/sgx/driver.c
+++ b/arch/x86/kernel/cpu/sgx/driver.c
@@ -150,6 +150,13 @@ static struct miscdevice sgx_dev_enclave = {
.fops = &sgx_encl_fops,
};

+static struct miscdevice sgx_dev_provision = {
+ .minor = MISC_DYNAMIC_MINOR,
+ .name = "provision",
+ .nodename = "sgx/provision",
+ .fops = &sgx_provision_fops,
+};
+
int __init sgx_drv_init(void)
{
unsigned int eax, ebx, ecx, edx;
@@ -190,5 +197,12 @@ int __init sgx_drv_init(void)
return ret;
}

+ ret = misc_register(&sgx_dev_provision);
+ if (ret) {
+ pr_err("Creating /dev/sgx/provision failed with %d.\n", ret);
+ misc_deregister(&sgx_dev_enclave);
+ return ret;
+ }
+
return 0;
}
diff --git a/arch/x86/kernel/cpu/sgx/driver.h b/arch/x86/kernel/cpu/sgx/driver.h
index e4063923115b..72747d01c046 100644
--- a/arch/x86/kernel/cpu/sgx/driver.h
+++ b/arch/x86/kernel/cpu/sgx/driver.h
@@ -23,6 +23,8 @@ extern u64 sgx_attributes_reserved_mask;
extern u64 sgx_xfrm_reserved_mask;
extern u32 sgx_xsave_size_tbl[64];

+extern const struct file_operations sgx_provision_fops;
+
long sgx_ioctl(struct file *filep, unsigned int cmd, unsigned long arg);

int sgx_drv_init(void);
diff --git a/arch/x86/kernel/cpu/sgx/ioctl.c b/arch/x86/kernel/cpu/sgx/ioctl.c
index 83513cdfd1c0..262001df3ae4 100644
--- a/arch/x86/kernel/cpu/sgx/ioctl.c
+++ b/arch/x86/kernel/cpu/sgx/ioctl.c
@@ -663,6 +663,50 @@ static long sgx_ioc_enclave_init(struct sgx_encl *encl, void __user *arg)
return ret;
}

+/**
+ * sgx_ioc_enclave_set_attribute - handler for %SGX_IOC_ENCLAVE_SET_ATTRIBUTE
+ * @filep: open file to /dev/sgx
+ * @arg: userspace pointer to a struct sgx_enclave_set_attribute instance
+ *
+ * Mark the enclave as being allowed to access a restricted attribute bit.
+ * The requested attribute is specified via the attribute_fd field in the
+ * provided struct sgx_enclave_set_attribute. The attribute_fd must be a
+ * handle to an SGX attribute file, e.g. “/dev/sgx/provision".
+ *
+ * Failure to explicitly request access to a restricted attribute will cause
+ * sgx_ioc_enclave_init() to fail. Currently, the only restricted attribute
+ * is access to the PROVISION_KEY.
+ *
+ * Note, access to the EINITTOKEN_KEY is disallowed entirely.
+ *
+ * Return: 0 on success, -errno otherwise
+ */
+static long sgx_ioc_enclave_set_attribute(struct sgx_encl *encl,
+ void __user *arg)
+{
+ struct sgx_enclave_set_attribute params;
+ struct file *attribute_file;
+ int ret;
+
+ if (copy_from_user(&params, arg, sizeof(params)))
+ return -EFAULT;
+
+ attribute_file = fget(params.attribute_fd);
+ if (!attribute_file)
+ return -EINVAL;
+
+ if (attribute_file->f_op != &sgx_provision_fops) {
+ ret = -EINVAL;
+ goto out;
+ }
+
+ encl->allowed_attributes |= SGX_ATTR_PROVISIONKEY;
+ ret = 0;
+
+out:
+ fput(attribute_file);
+ return ret;
+}

long sgx_ioctl(struct file *filep, unsigned int cmd, unsigned long arg)
{
@@ -686,6 +730,9 @@ long sgx_ioctl(struct file *filep, unsigned int cmd, unsigned long arg)
case SGX_IOC_ENCLAVE_INIT:
ret = sgx_ioc_enclave_init(encl, (void __user *)arg);
break;
+ case SGX_IOC_ENCLAVE_SET_ATTRIBUTE:
+ ret = sgx_ioc_enclave_set_attribute(encl, (void __user *)arg);
+ break;
default:
ret = -ENOIOCTLCMD;
break;
--
2.20.1