linux-kernel - Re: [PATCH v2 03/25] x86/sgx: Wipe out EREMOVE from sgx_free_epc

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Date:   Wed, 10 Mar 2021 22:35:10 +1300
From:   Kai Huang <kai.huang@...el.com>
To:     Kai Huang <kai.huang@...el.com>
Cc:     <kvm@...r.kernel.org>, <x86@...nel.org>,
        <linux-sgx@...r.kernel.org>, <linux-kernel@...r.kernel.org>,
        <seanjc@...gle.com>, <jarkko@...nel.org>, <luto@...nel.org>,
        <dave.hansen@...el.com>, <rick.p.edgecombe@...el.com>,
        <haitao.huang@...el.com>, <pbonzini@...hat.com>, <bp@...en8.de>,
        <tglx@...utronix.de>, <mingo@...hat.com>, <hpa@...or.com>
Subject: Re: [PATCH v2 03/25] x86/sgx: Wipe out EREMOVE from
 sgx_free_epc_page()

On Tue, 9 Mar 2021 14:39:01 +1300 Kai Huang wrote:
> From: Jarkko Sakkinen <jarkko@...nel.org>
> 
> EREMOVE takes a page and removes any association between that page and
> an enclave.  It must be run on a page before it can be added into
> another enclave.  Currently, EREMOVE is run as part of pages being freed
> into the SGX page allocator.  It is not expected to fail.
> 
> KVM does not track how guest pages are used, which means that SGX
> virtualization use of EREMOVE might fail.
> 
> Break out the EREMOVE call from the SGX page allocator.  This will allow
> the SGX virtualization code to use the allocator directly.  (SGX/KVM
> will also introduce a more permissive EREMOVE helper).
> 
> Implement original sgx_free_epc_page() as sgx_encl_free_epc_page() to be
> more specific that it is used to free EPC page assigned to one enclave.
> Print an error message when EREMOVE fails to explicitly call out EPC
> page is leaked, and requires machine reboot to get leaked pages back.
> 
> Signed-off-by: Jarkko Sakkinen <jarkko@...nel.org>
> Co-developed-by: Kai Huang <kai.huang@...el.com>
> Signed-off-by: Kai Huang <kai.huang@...el.com>
> ---
> v1->v2:
> 
>  - Merge original WARN() and pr_err_once() into one single WARN(), suggested
>    by Sean.
> 
> ---
>  arch/x86/kernel/cpu/sgx/encl.c | 27 ++++++++++++++++++++++++---
>  arch/x86/kernel/cpu/sgx/main.c | 12 ++++--------
>  2 files changed, 28 insertions(+), 11 deletions(-)
> 
> diff --git a/arch/x86/kernel/cpu/sgx/encl.c b/arch/x86/kernel/cpu/sgx/encl.c
> index 7449ef33f081..dcbcf840c522 100644
> --- a/arch/x86/kernel/cpu/sgx/encl.c
> +++ b/arch/x86/kernel/cpu/sgx/encl.c
> @@ -381,6 +381,27 @@ const struct vm_operations_struct sgx_vm_ops = {
>  	.access = sgx_vma_access,
>  };
>  
> +static void sgx_encl_free_epc_page(struct sgx_epc_page *epc_page)
> +{
> +	int ret;
> +
> +	WARN_ON_ONCE(epc_page->flags & SGX_EPC_PAGE_RECLAIMER_TRACKED);
> +
> +	/*
> +	 * Give a message to remind EPC page is leaked when EREMOVE fails,
> +	 * and requires machine reboot to get leaked pages back. This can
> +	 * be improved in future by adding stats of leaked pages, etc.
> +	 */
> +#define EREMOVE_ERROR_MESSAGE \
> +	"EREMOVE returned %d (0x%x).  EPC page leaked.  Reboot required to retrieve leaked pages."
> +	ret = __eremove(sgx_get_epc_virt_addr(epc_page));
> +	if (WARN_ONCE(ret, EREMOVE_ERROR_MESSAGE, ret, ret))
> +		return;
> +#undef EREMOVE_ERROR_MESSAGE
> +
> +	sgx_free_epc_page(epc_page);
> +}
> +
>  /**
>   * sgx_encl_release - Destroy an enclave instance
>   * @kref:	address of a kref inside &sgx_encl
> @@ -404,7 +425,7 @@ void sgx_encl_release(struct kref *ref)
>  			if (sgx_unmark_page_reclaimable(entry->epc_page))
>  				continue;
>  
> -			sgx_free_epc_page(entry->epc_page);
> +			sgx_encl_free_epc_page(entry->epc_page);
>  			encl->secs_child_cnt--;
>  			entry->epc_page = NULL;
>  		}
> @@ -415,7 +436,7 @@ void sgx_encl_release(struct kref *ref)
>  	xa_destroy(&encl->page_array);
>  
>  	if (!encl->secs_child_cnt && encl->secs.epc_page) {
> -		sgx_free_epc_page(encl->secs.epc_page);
> +		sgx_encl_free_epc_page(entry->epc_page);

Sorry. A mistake during copy/paste. Will fix.

>  		encl->secs.epc_page = NULL;
>  	}
>  
> @@ -423,7 +444,7 @@ 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_encl_free_epc_page(entry->epc_page);

Sorry. A mistake during copy/paste. Will fix.

>  		kfree(va_page);
>  	}
>  
> diff --git a/arch/x86/kernel/cpu/sgx/main.c b/arch/x86/kernel/cpu/sgx/main.c
> index 8df81a3ed945..44fe91a5bfb3 100644
> --- a/arch/x86/kernel/cpu/sgx/main.c
> +++ b/arch/x86/kernel/cpu/sgx/main.c
> @@ -598,18 +598,14 @@ 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 caller's
> + * 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;
> -
> -	WARN_ON_ONCE(page->flags & SGX_EPC_PAGE_RECLAIMER_TRACKED);
> -
> -	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
>