Re: [RFC PATCH v3 15/27] x86/sgx: Move provisioning device creation out of SGX driver

[Jarkko Sakkinen <jarkko@kernel.org>]

On Tue, Jan 26, 2021 at 10:31:07PM +1300, Kai Huang wrote:
> From: Sean Christopherson <sean.j.christopherson@intel.com>
> 
> And extract sgx_set_attribute() out of sgx_ioc_enclave_provision() and
> export it as symbol for KVM to use.
> 
> Provisioning key is sensitive. SGX driver only allows to create enclave
> which can access provisioning key when enclave creator has permission to
> open /dev/sgx_provision.  It should apply to VM as well, as provisioning
> key is platform specific, thus unrestricted VM can also potentially
> compromise provisioning key.
> 
> Move provisioning device creation out of sgx_drv_init() to sgx_init() as
> preparation for adding SGX virtualization support, so that even SGX
> driver is not enabled due to flexible launch control is not available,
> SGX virtualization can still be enabled, and use it to restrict VM's
> capability of being able to access provisioning key.
> 
> Signed-off-by: Sean Christopherson <sean.j.christopherson@intel.com>
> Signed-off-by: Kai Huang <kai.huang@intel.com>


Reviewed-by: Jarkko Sakkinen <jarkko@kernel.org>

/Jarkko

> ---
> v2->v3:
> 
>  - Added kdoc for sgx_set_attribute(), per Jarkko.
> 
> ---
>  arch/x86/include/asm/sgx.h       |  3 ++
>  arch/x86/kernel/cpu/sgx/driver.c | 17 ----------
>  arch/x86/kernel/cpu/sgx/ioctl.c  | 16 ++-------
>  arch/x86/kernel/cpu/sgx/main.c   | 58 +++++++++++++++++++++++++++++++-
>  4 files changed, 62 insertions(+), 32 deletions(-)
> 
> diff --git a/arch/x86/include/asm/sgx.h b/arch/x86/include/asm/sgx.h
> index 8a3ea3e1efbe..d67afb051db3 100644
> --- a/arch/x86/include/asm/sgx.h
> +++ b/arch/x86/include/asm/sgx.h
> @@ -4,6 +4,9 @@
>  
>  #include <linux/types.h>
>  
> +int sgx_set_attribute(unsigned long *allowed_attributes,
> +		      unsigned int attribute_fd);
> +
>  #ifdef CONFIG_X86_SGX_KVM
>  struct sgx_pageinfo;
>  
> diff --git a/arch/x86/kernel/cpu/sgx/driver.c b/arch/x86/kernel/cpu/sgx/driver.c
> index f2eac41bb4ff..4f3241109bda 100644
> --- a/arch/x86/kernel/cpu/sgx/driver.c
> +++ b/arch/x86/kernel/cpu/sgx/driver.c
> @@ -133,10 +133,6 @@ static const struct file_operations sgx_encl_fops = {
>  	.get_unmapped_area	= sgx_get_unmapped_area,
>  };
>  
> -const struct file_operations sgx_provision_fops = {
> -	.owner			= THIS_MODULE,
> -};
> -
>  static struct miscdevice sgx_dev_enclave = {
>  	.minor = MISC_DYNAMIC_MINOR,
>  	.name = "sgx_enclave",
> @@ -144,13 +140,6 @@ static struct miscdevice sgx_dev_enclave = {
>  	.fops = &sgx_encl_fops,
>  };
>  
> -static struct miscdevice sgx_dev_provision = {
> -	.minor = MISC_DYNAMIC_MINOR,
> -	.name = "sgx_provision",
> -	.nodename = "sgx_provision",
> -	.fops = &sgx_provision_fops,
> -};
> -
>  int __init sgx_drv_init(void)
>  {
>  	unsigned int eax, ebx, ecx, edx;
> @@ -184,11 +173,5 @@ int __init sgx_drv_init(void)
>  	if (ret)
>  		return ret;
>  
> -	ret = misc_register(&sgx_dev_provision);
> -	if (ret) {
> -		misc_deregister(&sgx_dev_enclave);
> -		return ret;
> -	}
> -
>  	return 0;
>  }
> diff --git a/arch/x86/kernel/cpu/sgx/ioctl.c b/arch/x86/kernel/cpu/sgx/ioctl.c
> index 1bae754268d1..4714de12422d 100644
> --- a/arch/x86/kernel/cpu/sgx/ioctl.c
> +++ b/arch/x86/kernel/cpu/sgx/ioctl.c
> @@ -2,6 +2,7 @@
>  /*  Copyright(c) 2016-20 Intel Corporation. */
>  
>  #include <asm/mman.h>
> +#include <asm/sgx.h>
>  #include <linux/mman.h>
>  #include <linux/delay.h>
>  #include <linux/file.h>
> @@ -664,24 +665,11 @@ static long sgx_ioc_enclave_init(struct sgx_encl *encl, void __user *arg)
>  static long sgx_ioc_enclave_provision(struct sgx_encl *encl, void __user *arg)
>  {
>  	struct sgx_enclave_provision params;
> -	struct file *file;
>  
>  	if (copy_from_user(&params, arg, sizeof(params)))
>  		return -EFAULT;
>  
> -	file = fget(params.fd);
> -	if (!file)
> -		return -EINVAL;
> -
> -	if (file->f_op != &sgx_provision_fops) {
> -		fput(file);
> -		return -EINVAL;
> -	}
> -
> -	encl->attributes_mask |= SGX_ATTR_PROVISIONKEY;
> -
> -	fput(file);
> -	return 0;
> +	return sgx_set_attribute(&encl->attributes_mask, params.fd);
>  }
>  
>  long sgx_ioctl(struct file *filep, unsigned int cmd, unsigned long arg)
> diff --git a/arch/x86/kernel/cpu/sgx/main.c b/arch/x86/kernel/cpu/sgx/main.c
> index b456899a9532..fba3eaf2ae26 100644
> --- a/arch/x86/kernel/cpu/sgx/main.c
> +++ b/arch/x86/kernel/cpu/sgx/main.c
> @@ -1,14 +1,18 @@
>  // SPDX-License-Identifier: GPL-2.0
>  /*  Copyright(c) 2016-20 Intel Corporation. */
>  
> +#include <linux/file.h>
>  #include <linux/freezer.h>
>  #include <linux/highmem.h>
>  #include <linux/kthread.h>
> +#include <linux/miscdevice.h>
>  #include <linux/pagemap.h>
>  #include <linux/ratelimit.h>
>  #include <linux/sched/mm.h>
>  #include <linux/sched/signal.h>
>  #include <linux/slab.h>
> +#include <asm/sgx_arch.h>
> +#include <asm/sgx.h>
>  #include "driver.h"
>  #include "encl.h"
>  #include "encls.h"
> @@ -712,6 +716,51 @@ void sgx_update_lepubkeyhash(u64 *lepubkeyhash)
>  		wrmsrl(MSR_IA32_SGXLEPUBKEYHASH0 + i, lepubkeyhash[i]);
>  }
>  
> +const struct file_operations sgx_provision_fops = {
> +	.owner			= THIS_MODULE,
> +};
> +
> +static struct miscdevice sgx_dev_provision = {
> +	.minor = MISC_DYNAMIC_MINOR,
> +	.name = "sgx_provision",
> +	.nodename = "sgx_provision",
> +	.fops = &sgx_provision_fops,
> +};
> +
> +/**
> + * sgx_set_attribute() - Update allowed attributes given file descriptor
> + * @allowed_attributes: 	Pointer to allowed enclave attributes
> + * @attribute_fd:		File descriptor for specific attribute
> + *
> + * Append enclave attribute indicated by file descriptor to allowed
> + * attributes. Currently only SGX_ATTR_PROVISIONKEY indicated by
> + * /dev/sgx_provision is supported.
> + *
> + * Return:
> + * -0:		SGX_ATTR_PROVISIONKEY is appended to allowed_attributes
> + * -EINVAL:	Invalid, or not supported file descriptor
> + */
> +int sgx_set_attribute(unsigned long *allowed_attributes,
> +		      unsigned int attribute_fd)
> +{
> +	struct file *file;
> +
> +	file = fget(attribute_fd);
> +	if (!file)
> +		return -EINVAL;
> +
> +	if (file->f_op != &sgx_provision_fops) {
> +		fput(file);
> +		return -EINVAL;
> +	}
> +
> +	*allowed_attributes |= SGX_ATTR_PROVISIONKEY;
> +
> +	fput(file);
> +	return 0;
> +}
> +EXPORT_SYMBOL_GPL(sgx_set_attribute);
> +
>  static int __init sgx_init(void)
>  {
>  	int ret;
> @@ -728,13 +777,20 @@ static int __init sgx_init(void)
>  		goto err_page_cache;
>  	}
>  
> +	ret = misc_register(&sgx_dev_provision);
> +	if (ret)
> +		goto err_kthread;
> +
>  	/* Success if the native *or* virtual EPC driver initialized cleanly. */
>  	ret = !!sgx_drv_init() & !!sgx_vepc_init();
>  	if (ret)
> -		goto err_kthread;
> +		goto err_provision;
>  
>  	return 0;
>  
> +err_provision:
> +	misc_deregister(&sgx_dev_provision);
> +
>  err_kthread:
>  	kthread_stop(ksgxd_tsk);
>  
> -- 
> 2.29.2
> 
>