Re: [PATCH V3 18/30] x86/sgx: Support complete page removal

[Jarkko Sakkinen]

On Mon, Apr 04, 2022 at 09:49:26AM -0700, Reinette Chatre wrote:
> The SGX2 page removal flow was introduced in previous patch and is
> as follows:
> 1) Change the type of the pages to be removed to SGX_PAGE_TYPE_TRIM
>    using the ioctl() SGX_IOC_ENCLAVE_MODIFY_TYPE introduced in
>    previous patch.
> 2) Approve the page removal by running ENCLU[EACCEPT] from within
>    the enclave.
> 3) Initiate actual page removal using the ioctl()
>    SGX_IOC_ENCLAVE_REMOVE_PAGES introduced here.
> 
> Support the final step of the SGX2 page removal flow with ioctl()
> SGX_IOC_ENCLAVE_REMOVE_PAGES. With this ioctl() the user specifies
> a page range that should be removed. All pages in the provided
> range should have the SGX_PAGE_TYPE_TRIM page type and the request
> will fail with EPERM (Operation not permitted) if a page that does
> not have the correct type is encountered. Page removal can fail
> on any page within the provided range. Support partial success by
> returning the number of pages that were successfully removed.
> 
> Since actual page removal will succeed even if ENCLU[EACCEPT] was not
> run from within the enclave the ENCLU[EMODPR] instruction with RWX
> permissions is used as a no-op mechanism to ensure ENCLU[EACCEPT] was
> successfully run from within the enclave before the enclave page is
> removed.
> 
> If the user omits running SGX_IOC_ENCLAVE_REMOVE_PAGES the pages will
> still be removed when the enclave is unloaded.
> 
> Signed-off-by: Reinette Chatre <reinette.chatre@xxxxxxxxx>
> ---
> Changes since V2:
> - Adjust ioctl number since removal of
>   SGX_IOC_ENCLAVE_RELAX_PERMISSIONS.
> 
> Changes since V1:
> - Update comments to refer to new ioctl() names SGX_IOC_PAGE_MODT ->
>   SGX_IOC_ENCLAVE_MODIFY_TYPE.
> - Fix kernel-doc to have () as part of function name.
> - Change name of ioctl():
>   SGX_IOC_PAGE_REMOVE -> SGX_IOC_ENCLAVE_REMOVE_PAGES (Jarkko).
> - With the above name change the page removal ioctl() has its name
>   aligned with existing SGX_IOC_ENCLAVE_ADD_PAGES ioctl(). Also align
>   naming of struct and functions:
>   struct sgx_page_remove -> struct sgx_enclave_remove_pages
>   sgx_page_remove() -> sgx_encl_remove_pages()
>   sgx_ioc_page_remove() -> sgx_ioc_enclave_remove_pages()
> - Use new SGX2 checking helper.
> - When loading enclave page, make error code consistent with other
>   instances to help user distinguish between permanent and temporary
>   failures.
> - Move kernel-doc to function that provides documentation for
>   Documentation/x86/sgx.rst.
> - Remove redundant comment.
> - Use offset/length validation utility.
> - Make explicit which member of struct sgx_enclave_remove_pages is for
>   output (Dave).
> 
>  arch/x86/include/uapi/asm/sgx.h |  21 +++++
>  arch/x86/kernel/cpu/sgx/ioctl.c | 145 ++++++++++++++++++++++++++++++++
>  2 files changed, 166 insertions(+)
> 
> diff --git a/arch/x86/include/uapi/asm/sgx.h b/arch/x86/include/uapi/asm/sgx.h
> index 529f4ab28410..feda7f85b2ce 100644
> --- a/arch/x86/include/uapi/asm/sgx.h
> +++ b/arch/x86/include/uapi/asm/sgx.h
> @@ -33,6 +33,8 @@ enum sgx_page_flags {
>  	_IOWR(SGX_MAGIC, 0x05, struct sgx_enclave_restrict_permissions)
>  #define SGX_IOC_ENCLAVE_MODIFY_TYPE \
>  	_IOWR(SGX_MAGIC, 0x06, struct sgx_enclave_modify_type)
> +#define SGX_IOC_ENCLAVE_REMOVE_PAGES \
> +	_IOWR(SGX_MAGIC, 0x07, struct sgx_enclave_remove_pages)
>  
>  /**
>   * struct sgx_enclave_create - parameter structure for the
> @@ -117,6 +119,25 @@ struct sgx_enclave_modify_type {
>  	__u64 count;
>  };
>  
> +/**
> + * struct sgx_enclave_remove_pages - %SGX_IOC_ENCLAVE_REMOVE_PAGES parameters
> + * @offset:	starting page offset (page aligned relative to enclave base
> + *		address defined in SECS)
> + * @length:	length of memory (multiple of the page size)
> + * @count:	(output) bytes successfully changed (multiple of page size)
> + *
> + * Regular (PT_REG) or TCS (PT_TCS) can be removed from an initialized
> + * enclave if the system supports SGX2. First, the %SGX_IOC_ENCLAVE_MODIFY_TYPE
> + * ioctl() should be used to change the page type to PT_TRIM. After that
> + * succeeds ENCLU[EACCEPT] should be run from within the enclave and then
> + * %SGX_IOC_ENCLAVE_REMOVE_PAGES can be used to complete the page removal.
> + */
> +struct sgx_enclave_remove_pages {
> +	__u64 offset;
> +	__u64 length;
> +	__u64 count;
> +};
> +
>  struct sgx_enclave_run;
>  
>  /**
> diff --git a/arch/x86/kernel/cpu/sgx/ioctl.c b/arch/x86/kernel/cpu/sgx/ioctl.c
> index 6f769e67ec2d..515e1961cc02 100644
> --- a/arch/x86/kernel/cpu/sgx/ioctl.c
> +++ b/arch/x86/kernel/cpu/sgx/ioctl.c
> @@ -1104,6 +1104,148 @@ static long sgx_ioc_enclave_modify_type(struct sgx_encl *encl, void __user *arg)
>  	return ret;
>  }
>  
> +/**
> + * sgx_encl_remove_pages() - Remove trimmed pages from SGX enclave
> + * @encl:	Enclave to which the pages belong
> + * @params:	Checked parameters from user on which pages need to be removed
> + *
> + * Return:
> + * - 0:		Success.
> + * - -errno:	Otherwise.
> + */
> +static long sgx_encl_remove_pages(struct sgx_encl *encl,
> +				  struct sgx_enclave_remove_pages *params)
> +{
> +	struct sgx_encl_page *entry;
> +	struct sgx_secinfo secinfo;
> +	unsigned long addr;
> +	unsigned long c;
> +	void *epc_virt;
> +	int ret;
> +
> +	memset(&secinfo, 0, sizeof(secinfo));
> +	secinfo.flags = SGX_SECINFO_R | SGX_SECINFO_W | SGX_SECINFO_X;
> +
> +	for (c = 0 ; c < params->length; c += PAGE_SIZE) {
> +		addr = encl->base + params->offset + c;
> +
> +		mutex_lock(&encl->lock);
> +
> +		entry = sgx_encl_load_page(encl, addr);
> +		if (IS_ERR(entry)) {
> +			ret = PTR_ERR(entry) == -EBUSY ? -EAGAIN : -EFAULT;
> +			goto out_unlock;
> +		}
> +
> +		if (entry->type != SGX_PAGE_TYPE_TRIM) {
> +			ret = -EPERM;
> +			goto out_unlock;
> +		}
> +
> +		/*
> +		 * ENCLS[EMODPR] is a no-op instruction used to inform if
> +		 * ENCLU[EACCEPT] was run from within the enclave. If
> +		 * ENCLS[EMODPR] is run with RWX on a trimmed page that is
> +		 * not yet accepted then it will return
> +		 * %SGX_PAGE_NOT_MODIFIABLE, after the trimmed page is
> +		 * accepted the instruction will encounter a page fault.
> +		 */
> +		epc_virt = sgx_get_epc_virt_addr(entry->epc_page);
> +		ret = __emodpr(&secinfo, epc_virt);
> +		if (!encls_faulted(ret) || ENCLS_TRAPNR(ret) != X86_TRAP_PF) {
> +			ret = -EPERM;
> +			goto out_unlock;
> +		}
> +
> +		if (sgx_unmark_page_reclaimable(entry->epc_page)) {
> +			ret = -EBUSY;
> +			goto out_unlock;
> +		}
> +
> +		/*
> +		 * Do not keep encl->lock because of dependency on
> +		 * mmap_lock acquired in sgx_zap_enclave_ptes().
> +		 */
> +		mutex_unlock(&encl->lock);
> +
> +		sgx_zap_enclave_ptes(encl, addr);
> +
> +		mutex_lock(&encl->lock);
> +
> +		sgx_encl_free_epc_page(entry->epc_page);
> +		encl->secs_child_cnt--;
> +		entry->epc_page = NULL;
> +		xa_erase(&encl->page_array, PFN_DOWN(entry->desc));
> +		sgx_encl_shrink(encl, NULL);
> +		kfree(entry);
> +
> +		mutex_unlock(&encl->lock);
> +	}
> +
> +	ret = 0;
> +	goto out;
> +
> +out_unlock:
> +	mutex_unlock(&encl->lock);
> +out:
> +	params->count = c;
> +
> +	return ret;
> +}
> +
> +/**
> + * sgx_ioc_enclave_remove_pages() - handler for %SGX_IOC_ENCLAVE_REMOVE_PAGES
> + * @encl:	an enclave pointer
> + * @arg:	userspace pointer to &struct sgx_enclave_remove_pages instance
> + *
> + * Final step of the flow removing pages from an initialized enclave. The
> + * complete flow is:
> + *
> + * 1) User changes the type of the pages to be removed to %SGX_PAGE_TYPE_TRIM
> + *    using the %SGX_IOC_ENCLAVE_MODIFY_TYPE ioctl().
> + * 2) User approves the page removal by running ENCLU[EACCEPT] from within
> + *    the enclave.
> + * 3) User initiates actual page removal using the
> + *    %SGX_IOC_ENCLAVE_REMOVE_PAGES ioctl() that is handled here.
> + *
> + * First remove any page table entries pointing to the page and then proceed
> + * with the actual removal of the enclave page and data in support of it.
> + *
> + * VA pages are not affected by this removal. It is thus possible that the
> + * enclave may end up with more VA pages than needed to support all its
> + * pages.
> + *
> + * Return:
> + * - 0:		Success
> + * - -errno:	Otherwise
> + */
> +static long sgx_ioc_enclave_remove_pages(struct sgx_encl *encl,
> +					 void __user *arg)
> +{
> +	struct sgx_enclave_remove_pages params;
> +	long ret;
> +
> +	ret = sgx_ioc_sgx2_ready(encl);
> +	if (ret)
> +		return ret;
> +
> +	if (copy_from_user(&params, arg, sizeof(params)))
> +		return -EFAULT;
> +
> +	if (sgx_validate_offset_length(encl, params.offset, params.length))
> +		return -EINVAL;
> +
> +	if (params.count)
> +		return -EINVAL;
> +
> +	ret = sgx_encl_remove_pages(encl, &params);
> +
> +	if (copy_to_user(arg, &params, sizeof(params)))
> +		return -EFAULT;
> +
> +	return ret;
> +}
> +
>  long sgx_ioctl(struct file *filep, unsigned int cmd, unsigned long arg)
>  {
>  	struct sgx_encl *encl = filep->private_data;
> @@ -1132,6 +1274,9 @@ long sgx_ioctl(struct file *filep, unsigned int cmd, unsigned long arg)
>  	case SGX_IOC_ENCLAVE_MODIFY_TYPE:
>  		ret = sgx_ioc_enclave_modify_type(encl, (void __user *)arg);
>  		break;
> +	case SGX_IOC_ENCLAVE_REMOVE_PAGES:
> +		ret = sgx_ioc_enclave_remove_pages(encl, (void __user *)arg);
> +		break;
>  	default:
>  		ret = -ENOIOCTLCMD;
>  		break;
> -- 
> 2.25.1
> 

Reviewed-by: Jarkko Sakkinen <jarkko@xxxxxxxxxx>

It's easy to give these quickly as I've spent at least a month looking at
this code while working on support for enarx run-time...

BR, Jarkko