Re: [PATCH v19 17/27] x86/sgx: Add provisioning

[Sean Christopherson <sean.j.christopherson@intel.com>]

On Sun, Mar 17, 2019 at 11:14:46PM +0200, Jarkko Sakkinen wrote:
> In order to provide a mechanism for devilering provisoning rights:
> 
> 1. Add a new file to the securityfs file called 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 token_fd;
>    };
> 
> A daemon could sit on top of 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 more or less straight-forward. Lets assume that
> dev_fd is a handle to /dev/sgx and prov_fd is a handle to 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: James Morris <jmorris@namei.org>
> Cc: Serge E. Hallyn <serge@hallyn.com>
> 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        | 13 +++++++
>  arch/x86/kernel/cpu/sgx/driver/ioctl.c | 43 +++++++++++++++++++++++
>  arch/x86/kernel/cpu/sgx/driver/main.c  | 47 ++++++++++++++++++++++++++
>  3 files changed, 103 insertions(+)
> 
> diff --git a/arch/x86/include/uapi/asm/sgx.h b/arch/x86/include/uapi/asm/sgx.h
> index aadf9c76e360..150a784db395 100644
> --- a/arch/x86/include/uapi/asm/sgx.h
> +++ b/arch/x86/include/uapi/asm/sgx.h
> @@ -16,6 +16,8 @@
>  	_IOW(SGX_MAGIC, 0x01, struct sgx_enclave_add_page)
>  #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)
>  
>  /* IOCTL return values */
>  #define SGX_POWER_LOST_ENCLAVE		0x40000000
> @@ -56,4 +58,15 @@ struct sgx_enclave_init {
>  	__u64	sigstruct;
>  };
>  
> +/**
> + * struct sgx_enclave_set_attribute - parameter structure for the
> + *				      %SGX_IOC_ENCLAVE_INIT ioctl
> + * @addr:		address within the ELRANGE
> + * @attribute_fd:	file handle of the attribute file in the securityfs
> + */
> +struct sgx_enclave_set_attribute {
> +	__u64	addr;
> +	__u64	attribute_fd;
> +};
> +
>  #endif /* _UAPI_ASM_X86_SGX_H */
> diff --git a/arch/x86/kernel/cpu/sgx/driver/ioctl.c b/arch/x86/kernel/cpu/sgx/driver/ioctl.c
> index 4b9a91b53b50..5d85bd3f7876 100644
> --- a/arch/x86/kernel/cpu/sgx/driver/ioctl.c
> +++ b/arch/x86/kernel/cpu/sgx/driver/ioctl.c
> @@ -759,6 +759,46 @@ static long sgx_ioc_enclave_init(struct file *filep, unsigned int cmd,
>  	return ret;
>  }
>  
> +/**
> + * sgx_ioc_enclave_set_attribute - handler for %SGX_IOC_ENCLAVE_SET_ATTRIBUTE
> + * @filep:	open file to /dev/sgx
> + * @cmd:	the command value
> + * @arg:	pointer to a struct sgx_enclave_set_attribute instance
> + *
> + * Sets an attribute matching the attribute file that is pointed by the
> + * parameter structure field attribute_fd.

With the @data change (see below), this becomes something like:

 * Allow the enclave to request the attribute managed by the SGX security file
 * pointed at by the parameter structure field attribute_fd.

> + *
> + * Return: 0 on success, -errno otherwise
> + */
> +static long sgx_ioc_enclave_set_attribute(struct file *filep, unsigned int cmd,
> +					  unsigned long arg)
> +{
> +	struct sgx_enclave_set_attribute *params = (void *)arg;
> +	struct file *attribute_file;
> +	struct sgx_encl *encl;
> +	int ret;
> +
> +	attribute_file = fget(params->attribute_fd);
> +	if (!attribute_file->f_op)

This should be:

	if (!attribute_file)
		return -EINVAL;

> +		return -EINVAL;
> +
> +	if (attribute_file->f_op != &sgx_fs_provision_fops) {
> +		ret = -EINVAL;
> +		goto out;
> +	}
> +
> +	ret = sgx_encl_get(params->addr, &encl);
> +	if (ret)
> +		goto out;
> +
> +	encl->allowed_attributes |= SGX_ATTR_PROVISIONKEY;

A cleanr approach would be to pass SGX_ATTR_PROVISIONKEY via @data to
securityfs_create_file().  Then you don't need to define dummy file_ops
for each file, i.e. a generic sgx_sec_fs_ops would suffice for the above
check.  And you don't have this weird hardcoding of the provision bit.

E.g.:

	if (attribute_file->f_op != &sgx_sec_fs_fops) {
		ret = -EINVAL;
		goto out;
	}

	ret = sgx_encl_get(params->addr, &encl);
	if (ret)
		goto out;

	encl->allowed_attributes |= (u64)attribute_file->private_data;

Since SGX doesn't support 32-bit builds we don't even need to worry about
the (very distant) future where SGX defines bits in the 63:32 range.


> +	kref_put(&encl->refcount, sgx_encl_release);
> +
> +out:
> +	fput(attribute_file);
> +	return ret;
> +}
> +
>  typedef long (*sgx_ioc_t)(struct file *filep, unsigned int cmd,
>  			  unsigned long arg);
>  
> @@ -778,6 +818,9 @@ long sgx_ioctl(struct file *filep, unsigned int cmd, unsigned long arg)
>  	case SGX_IOC_ENCLAVE_INIT:
>  		handler = sgx_ioc_enclave_init;
>  		break;
> +	case SGX_IOC_ENCLAVE_SET_ATTRIBUTE:
> +		handler = sgx_ioc_enclave_set_attribute;
> +		break;
>  	default:
>  		return -ENOIOCTLCMD;
>  	}
> diff --git a/arch/x86/kernel/cpu/sgx/driver/main.c b/arch/x86/kernel/cpu/sgx/driver/main.c
> index 16f36cd0af04..9a5360dcad98 100644
> --- a/arch/x86/kernel/cpu/sgx/driver/main.c
> +++ b/arch/x86/kernel/cpu/sgx/driver/main.c
> @@ -22,6 +22,11 @@ u64 sgx_attributes_reserved_mask;
>  u64 sgx_xfrm_reserved_mask = ~0x3;
>  u32 sgx_xsave_size_tbl[64];
>  
> +const struct file_operations sgx_fs_provision_fops;
> +
> +static struct dentry *sgx_fs;
> +static struct dentry *sgx_fs_provision;
> +
>  #ifdef CONFIG_COMPAT
>  static long sgx_compat_ioctl(struct file *filep, unsigned int cmd,
>  			      unsigned long arg)
> @@ -147,6 +152,40 @@ static struct sgx_dev_ctx *sgxm_dev_ctx_alloc(struct device *parent)
>  	return ctx;
>  }
>  
> +static int sgx_fs_init(struct device *dev)
> +{
> +	int ret;
> +
> +	sgx_fs = securityfs_create_dir(dev_name(dev), NULL);
> +	if (IS_ERR(sgx_fs)) {
> +		ret = PTR_ERR(sgx_fs);
> +		goto err_sgx_fs;
> +	}
> +
> +	sgx_fs_provision = securityfs_create_file("provision", 0600, sgx_fs,
> +						  NULL, &sgx_fs_provision_fops);

Per above, pass SGX_ATTR_PROVISIONKEY instead of NULL.

> +	if (IS_ERR(sgx_fs)) {
> +		ret = PTR_ERR(sgx_fs_provision);
> +		goto err_sgx_fs_provision;
> +	}
> +
> +	return 0;
> +
> +err_sgx_fs_provision:
> +	securityfs_remove(sgx_fs);
> +	sgx_fs_provision = NULL;
> +
> +err_sgx_fs:
> +	sgx_fs = NULL;
> +	return ret;
> +}
> +
> +static void sgx_fs_remove(void)
> +{
> +	securityfs_remove(sgx_fs_provision);
> +	securityfs_remove(sgx_fs);
> +}
> +
>  static int sgx_dev_init(struct device *parent)
>  {
>  	struct sgx_dev_ctx *sgx_dev;
> @@ -190,6 +229,10 @@ static int sgx_dev_init(struct device *parent)
>  	if (!sgx_encl_wq)
>  		return -ENOMEM;
>  
> +	ret = sgx_fs_init(&sgx_dev->ctrl_dev);
> +	if (ret)
> +		goto err_fs_init;
> +
>  	ret = cdev_device_add(&sgx_dev->ctrl_cdev, &sgx_dev->ctrl_dev);
>  	if (ret)
>  		goto err_device_add;
> @@ -197,6 +240,9 @@ static int sgx_dev_init(struct device *parent)
>  	return 0;
>  
>  err_device_add:
> +	sgx_fs_remove();
> +
> +err_fs_init:
>  	destroy_workqueue(sgx_encl_wq);
>  	return ret;
>  }
> @@ -220,6 +266,7 @@ static int sgx_drv_remove(struct platform_device *pdev)
>  {
>  	struct sgx_dev_ctx *ctx = dev_get_drvdata(&pdev->dev);
>  
> +	sgx_fs_remove();
>  	cdev_device_del(&ctx->ctrl_cdev, &ctx->ctrl_dev);
>  	destroy_workqueue(sgx_encl_wq);
>  
> -- 
> 2.19.1
>