Re: [PATCH v2 2/2] x86/sgx: Wipe out EREMOVE from sgx_free_epc_page()

[Kai Huang <kai.huang@intel.com>]

On Wed, 13 Jan 2021 01:33:51 +0200 jarkko@kernel.org wrote:
> From: "jarkko@kernel.org" <jarkko@kernel.org>
> 
> Encapsulate the snippet in sgx_free_epc_page() concerning EREMOVE to
> sgx_reset_epc_page(), which is a static helper function for
> sgx_encl_release(). It's the only function existing, which deals with
> initialized pages.
> 
> Signed-off-by: jarkko@kernel.org <jarkko@kernel.org>
> ---
> v2: Fixed a compilation error s/page/epc_page/ change not amended
>     to the patches.
>  arch/x86/kernel/cpu/sgx/encl.c | 15 ++++++++++++++-
>  arch/x86/kernel/cpu/sgx/main.c | 10 ++++------
>  2 files changed, 18 insertions(+), 7 deletions(-)
> 
> diff --git a/arch/x86/kernel/cpu/sgx/encl.c b/arch/x86/kernel/cpu/sgx/encl.c
> index fe7256db6e73..511f4bc70699 100644
> --- a/arch/x86/kernel/cpu/sgx/encl.c
> +++ b/arch/x86/kernel/cpu/sgx/encl.c
> @@ -389,6 +389,16 @@ const struct vm_operations_struct sgx_vm_ops = {
>  	.access = sgx_vma_access,
>  };
>  
> +
> +static void sgx_reset_epc_page(struct sgx_epc_page *epc_page)
> +{
> +	int ret;
> +
> +	ret = __eremove(sgx_get_epc_virt_addr(epc_page));
> +	if (WARN_ONCE(ret, "EREMOVE returned %d (0x%x)", ret, ret))
> +		return;
> +}
> +
>  /**
>   * sgx_encl_release - Destroy an enclave instance
>   * @kref:	address of a kref inside &sgx_encl
> @@ -412,6 +422,7 @@ void sgx_encl_release(struct kref *ref)
>  			if (sgx_unmark_page_reclaimable(entry->epc_page))
>  				continue;
>  
> +			sgx_reset_epc_page(entry->epc_page);
>  			sgx_free_epc_page(entry->epc_page);
>  			encl->secs_child_cnt--;
>  			entry->epc_page = NULL;
> @@ -423,6 +434,7 @@ void sgx_encl_release(struct kref *ref)
>  	xa_destroy(&encl->page_array);
>  
>  	if (!encl->secs_child_cnt && encl->secs.epc_page) {
> +		sgx_reset_epc_page(encl->secs.epc_page);
>  		sgx_free_epc_page(encl->secs.epc_page);
>  		encl->secs.epc_page = NULL;
>  	}
> @@ -431,7 +443,8 @@ void sgx_encl_release(struct kref *ref)
>  		va_page = list_first_entry(&encl->va_pages, struct sgx_va_page,
>  					   list);
>  		list_del(&va_page->list);
> -		sgx_free_epc_page(va_page->epc_page);
> +		sgx_reset_epc_page(entry->epc_page);
> +		sgx_free_epc_page(entry->epc_page);

Reply so that Sean can see, since he just subscribed to linux-sgx list.

As Sean pointed out in KVM SGX virtualization thread, entry should be va_page.

>  		kfree(va_page);
>  	}
>  
> diff --git a/arch/x86/kernel/cpu/sgx/main.c b/arch/x86/kernel/cpu/sgx/main.c
> index b2996cb63a8a..89d52fb56d4b 100644
> --- a/arch/x86/kernel/cpu/sgx/main.c
> +++ b/arch/x86/kernel/cpu/sgx/main.c
> @@ -629,16 +629,14 @@ struct sgx_epc_page *sgx_alloc_epc_page(void *owner, bool reclaim)
>   * sgx_free_epc_page() - Free an EPC page
>   * @page:	an EPC page
>   *
> - * Call EREMOVE for an EPC page and insert it back to the list of free pages.
> + * Put the EPC page back to the list of free pages. It's the callers
> + * responsibility to make sure that the page is in uninitialized state In other
> + * words, do EREMOVE, EWB or whatever operation is necessary before calling
> + * this function.
>   */
>  void sgx_free_epc_page(struct sgx_epc_page *page)
>  {
>  	struct sgx_epc_section *section = &sgx_epc_sections[page->section];
> -	int ret;
> -
> -	ret = __eremove(sgx_get_epc_virt_addr(page));
> -	if (WARN_ONCE(ret, "EREMOVE returned %d (0x%x)", ret, ret))
> -		return;
>  
>  	spin_lock(&section->lock);
>  	list_add_tail(&page->list, &section->page_list);
> -- 
> 2.29.2
>