On Thursday, 2020-07-16 at 16:52:54 +03, Jarkko Sakkinen wrote:
> Provisioning Certification Enclave (PCE), the root of trust for other
> enclaves, generates a signing key from a fused key called Provisioning
> Certification Key. PCE can then use this key to certify an attestation key
> of a Quoting Enclave (QE), e.g. we get the chain of trust down to the
> hardware if the Intel signed PCE is used.
>
> To use the needed keys, ATTRIBUTE.PROVISIONKEY is required but should be
> only allowed for those who actually need it so that only the trusted
> parties can certify QE's.
>
> Obviously the attestation service should know the public key of the used
> PCE and that way detect illegit attestation, but whitelisting the legit
> users still adds an additional layer of defence.
>
> Add new device file called /dev/sgx/provision. The sole purpose of this
> file is to provide file descriptors that act as privilege tokens to allow
> to build enclaves with ATTRIBUTE.PROVISIONKEY set. A new ioctl called
> SGX_IOC_ENCLAVE_SET_ATTRIBUTE is used to assign this token to an enclave.
>
> Cc: linux-security-mod...@vger.kernel.org
> Acked-by: Jethro Beekman <jet...@fortanix.com>
> Suggested-by: Andy Lutomirski <l...@kernel.org>
> Signed-off-by: Jarkko Sakkinen <jarkko.sakki...@linux.intel.com>
Reviewed-by: Darren Kenny <darren.ke...@oracle.com>
> ---
> arch/x86/include/uapi/asm/sgx.h | 11 ++++++++
> arch/x86/kernel/cpu/sgx/driver.c | 18 ++++++++++++
> arch/x86/kernel/cpu/sgx/driver.h | 2 ++
> arch/x86/kernel/cpu/sgx/ioctl.c | 47 ++++++++++++++++++++++++++++++++
> 4 files changed, 78 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 5559bc18de41..b9af330a16fa 100644
> --- a/arch/x86/kernel/cpu/sgx/driver.c
> +++ b/arch/x86/kernel/cpu/sgx/driver.c
> @@ -138,6 +138,10 @@ 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 = "enclave",
> @@ -145,6 +149,13 @@ 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;
> @@ -185,5 +196,12 @@ 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 3444de955191..95b0a1e62ea7 100644
> --- a/arch/x86/kernel/cpu/sgx/ioctl.c
> +++ b/arch/x86/kernel/cpu/sgx/ioctl.c
> @@ -669,6 +669,50 @@ 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(¶ms, 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)
> {
> @@ -694,6 +738,9 @@ 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;
> --
> 2.25.1
