From mboxrd@z Thu Jan 1 00:00:00 1970 Return-Path: X-Spam-Checker-Version: SpamAssassin 3.4.0 (2014-02-07) on aws-us-west-2-korg-lkml-1.web.codeaurora.org Received: from vger.kernel.org (vger.kernel.org [23.128.96.18]) by smtp.lore.kernel.org (Postfix) with ESMTP id D53ABC433EF for ; Thu, 17 Mar 2022 07:12:22 +0000 (UTC) Received: (majordomo@vger.kernel.org) by vger.kernel.org via listexpand id S230168AbiCQHNh (ORCPT ); Thu, 17 Mar 2022 03:13:37 -0400 Received: from lindbergh.monkeyblade.net ([23.128.96.19]:50556 "EHLO lindbergh.monkeyblade.net" rhost-flags-OK-OK-OK-OK) by vger.kernel.org with ESMTP id S230031AbiCQHNf (ORCPT ); Thu, 17 Mar 2022 03:13:35 -0400 Received: from dfw.source.kernel.org (dfw.source.kernel.org [IPv6:2604:1380:4641:c500::1]) by lindbergh.monkeyblade.net (Postfix) with ESMTPS id C7FE716A6A7; Thu, 17 Mar 2022 00:12:19 -0700 (PDT) Received: from smtp.kernel.org (relay.kernel.org [52.25.139.140]) (using TLSv1.2 with cipher ECDHE-RSA-AES256-GCM-SHA384 (256/256 bits)) (No client certificate requested) by dfw.source.kernel.org (Postfix) with ESMTPS id 57D73612FC; Thu, 17 Mar 2022 07:12:19 +0000 (UTC) Received: by smtp.kernel.org (Postfix) with ESMTPSA id 37790C340E9; Thu, 17 Mar 2022 07:12:18 +0000 (UTC) DKIM-Signature: v=1; a=rsa-sha256; c=relaxed/simple; d=kernel.org; s=k20201202; t=1647501138; bh=KgNHp5UtA+XTjbpsJS9b38tGdPvseTfHTAntYwQVbQ8=; h=Date:From:To:Cc:Subject:References:In-Reply-To:From; b=QX4Usa9E6tfR7ySnyycPJNu2ur3MT8VOvJeJOx2OwZ+HcPug0zl2wREFI7hHwTu5V AzL9WrmnaMHqmTOhVxRLHngfh/TbYs2Yt/tmolOnGyDfLPChPfzE9BWU3eNmQbOqba pRtLR+CyuZiwLIbU+h1gMy8+C41+kqvLH1SeJrwOCyChtDjAC8dZhTnMtnmJXydNaH XtaCX4q2RCuAGrfDQxAVJ4Jxa0NfWu9iiGqBDDbY7WJIjFOPxK+oh72H6gC+4+H+py odvdpZ5XhXYlfzZEyqwCZGFk+4FJHncfC9QYss70oow/mZJ4Q0iQLJ1tZTPspo9oCl thp18aown5SXQ== Date: Thu, 17 Mar 2022 09:11:28 +0200 From: Jarkko Sakkinen To: Haitao Huang Cc: Reinette Chatre , "Dhanraj, Vijay" , "dave.hansen@linux.intel.com" , "tglx@linutronix.de" , "bp@alien8.de" , "Lutomirski, Andy" , "mingo@redhat.com" , "linux-sgx@vger.kernel.org" , "x86@kernel.org" , "Christopherson,, Sean" , "Huang, Kai" , "Zhang, Cathy" , "Xing, Cedric" , "Huang, Haitao" , "Shanahan, Mark" , "hpa@zytor.com" , "linux-kernel@vger.kernel.org" , nathaniel@profian.com Subject: Re: [PATCH V2 16/32] x86/sgx: Support restricting of enclave page permissions Message-ID: References: <97565fed-dc67-bab1-28d4-c40201c9f055@intel.com> MIME-Version: 1.0 Content-Type: text/plain; charset=us-ascii Content-Disposition: inline In-Reply-To: Precedence: bulk List-ID: X-Mailing-List: linux-kernel@vger.kernel.org On Thu, Mar 17, 2022 at 09:01:07AM +0200, Jarkko Sakkinen wrote: > On Mon, Mar 14, 2022 at 10:39:36AM -0500, Haitao Huang wrote: > > Hi Jarkko > > > > On Sun, 13 Mar 2022 21:58:51 -0500, Jarkko Sakkinen > > wrote: > > > > > On Mon, Mar 14, 2022 at 04:50:56AM +0200, Jarkko Sakkinen wrote: > > > > On Mon, Mar 14, 2022 at 04:49:37AM +0200, Jarkko Sakkinen wrote: > > > > > On Fri, Mar 11, 2022 at 09:53:29AM -0800, Reinette Chatre wrote: > > > > > > > > > > > I saw Haitao's note that EMODPE requires "Read access permitted > > > > by enclave". > > > > > > This motivates that EMODPR->PROT_NONE should not be allowed > > > > since it would > > > > > > not be possible to relax permissions (run EMODPE) after that. > > > > Even so, I > > > > > > also found in the SDM that EACCEPT has the note "Read access > > > > permitted > > > > > > by enclave". That seems to indicate that EMODPR->PROT_NONE is > > > > not practical > > > > > > from that perspective either since the enclave will not be able to > > > > > > EACCEPT the change. Does that match your understanding? > > > > > > > > > > Yes, PROT_NONE should not be allowed. > > > > > > > > > > This is however the real problem. > > > > > > > > > > The current kernel patch set has inconsistent API and EMODPR ioctl is > > > > > simply unacceptable. It also requires more concurrency management > > > > from > > > > > user space run-time, which would be heck a lot easier to do in the > > > > kernel. > > > > > > > > > > If you really want EMODPR as ioctl, then for consistencys sake, > > > > then EAUG > > > > > should be too. Like this when things go opposite directions, this > > > > patch set > > > > > plain and simply will not work out. > > > > > > > > > > I would pick EAUG's strategy from these two as it requires half > > > > the back > > > > > calls to host from an enclave. I.e. please combine mprotect() and > > > > EMODPR, > > > > > either in the #PF handler or as part of mprotect(), which ever > > > > suits you > > > > > best. > > > > > > > > > > I'll try demonstrate this with two examples. > > > > > > > > > > mmap() could go something like this() (simplified): > > > > > 1. Execution #UD's to SYSCALL. > > > > > 2. Host calls enclave's mmap() handler with mmap() parameters. > > > > > 3. Enclave up-calls host's mmap(). > > > > > 4. Loops the range with EACCEPTCOPY. > > > > > > > > > > mprotect() has to be done like this: > > > > > 1. Execution #UD's to SYSCALL. > > > > > 2. Host calls enclave's mprotect() handler. > > > > > 3. Enclave up-calls host's mprotect(). > > > > > 4. Enclave up-calls host's ioctl() to SGX_IOC_ENCLAVE_PERMISSIONS. > > > > I assume up-calls here are ocalls as we call them in our implementation, > > which are the calls enclave make to untrusted side via EEXIT. > > > > If so, can your implementation combine this two up-calls into one, then host > > side just do ioctl() and mprotect to kernel? If so, would that address your > > concern about extra up-calls? > > > > > > > > > 3. Loops the range with EACCEPT. > > > > ~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~ > > > > 5. Loops the range with EACCEPT + EMODPE. > > > > > > > > > This is just terrible IMHO. I hope these examples bring some insight. > > > > > > E.g. in Enarx we have to add a special up-call (so called enarxcall in > > > intermediate that we call sallyport, which provides shared buffer to > > > communicate with the enclave) just for reseting the range with PROT_READ. > > > Feel very redundant, adds ugly cruft and is completely opposite strategy > > > to > > > what you've chosen to do with EAUG, which is I think correct choice as > > > far > > > as API is concerned. > > > > The problem with EMODPR on #PF is that kernel needs to know what permissions > > requested from enclave at the time of #PF. So enclave has to make at least > > one call to kernel (again via ocall in our case, I assume up-call in your > > case) to make the change. > > The #PF handler should do unconditionally EMODPR with PROT_READ. Or mprotect(), as long as secinfo contains PROT_READ. I don't care about this detail hugely anymore because it does not affect uapi. Using EMODPR as a permission control mechanism is a ridiculous idea, and I cannot commit to maintain a broken uapi. BR, Jarkko