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Tue, 22 Sep 2020 05:35:26 +0000 (UTC) IronPort-SDR: 5Hy62Gt2FbKzM/D5UFNKWqZGYrKQ+yB2zPO7uvWLt4S6+i4eV4MSDo44BX5DTATsdHdJGIWcLk zYqvJMmudABA== X-IronPort-AV: E=McAfee;i="6000,8403,9751"; a="159821331" X-IronPort-AV: E=Sophos;i="5.77,289,1596524400"; d="scan'208";a="159821331" X-Amp-Result: SKIPPED(no attachment in message) X-Amp-File-Uploaded: False Received: from orsmga005.jf.intel.com ([10.7.209.41]) by fmsmga103.fm.intel.com with ESMTP/TLS/ECDHE-RSA-AES256-GCM-SHA384; 21 Sep 2020 22:35:24 -0700 IronPort-SDR: IjY1VHA7Mdgzde0do2ORSGHmGVo2ohZ1JRxey/zoMcwFSBrtHYawzvuYSM4lFdjoJmMWwQhD11 zTSA1Lu+wg6g== X-IronPort-AV: E=Sophos;i="5.77,289,1596524400"; d="scan'208";a="485807667" Received: from krodolf-mobl1.ger.corp.intel.com (HELO localhost) ([10.252.49.25]) by orsmga005-auth.jf.intel.com with ESMTP/TLS/ECDHE-RSA-AES256-GCM-SHA384; 21 Sep 2020 22:35:17 -0700 Date: Tue, 22 Sep 2020 08:35:15 +0300 From: Jarkko Sakkinen To: Sean Christopherson Cc: Andy Lutomirski , X86 ML , linux-sgx@vger.kernel.org, LKML , Linux-MM , Andrew Morton , Matthew Wilcox , Jethro Beekman , Darren Kenny , Andy Shevchenko , asapek@google.com, Borislav Petkov , "Xing, Cedric" , chenalexchen@google.com, Conrad Parker , cyhanish@google.com, Dave Hansen , "Huang, Haitao" , Josh Triplett , "Huang, Kai" , "Svahn, Kai" , Keith Moyer , Christian Ludloff , Neil Horman , Nathaniel McCallum , Patrick Uiterwijk , David Rientjes , Thomas Gleixner , yaozhangx@google.com Subject: Re: [PATCH v38 10/24] mm: Add vm_ops->mprotect() Message-ID: <20200922053515.GA97687@linux.intel.com> References: <20200915112842.897265-1-jarkko.sakkinen@linux.intel.com> <20200915112842.897265-11-jarkko.sakkinen@linux.intel.com> <20200918235337.GA21189@sjchrist-ice> <20200921124946.GF6038@linux.intel.com> <20200921165758.GA24156@linux.intel.com> <20200921210736.GB58176@linux.intel.com> <20200921211849.GA25403@linux.intel.com> <20200922052957.GA97272@linux.intel.com> MIME-Version: 1.0 Content-Type: text/plain; charset=us-ascii Content-Disposition: inline In-Reply-To: <20200922052957.GA97272@linux.intel.com> Organization: Intel Finland Oy - BIC 0357606-4 - Westendinkatu 7, 02160 Espoo X-Bogosity: Ham, tests=bogofilter, spamicity=0.000000, version=1.2.4 Sender: owner-linux-mm@kvack.org Precedence: bulk X-Loop: owner-majordomo@kvack.org List-ID: On Tue, Sep 22, 2020 at 08:30:06AM +0300, Jarkko Sakkinen wrote: > On Mon, Sep 21, 2020 at 02:18:49PM -0700, Sean Christopherson wrote: > > On Tue, Sep 22, 2020 at 12:07:36AM +0300, Jarkko Sakkinen wrote: > > > On Mon, Sep 21, 2020 at 09:57:58AM -0700, Sean Christopherson wrote: > > > > On Mon, Sep 21, 2020 at 03:49:46PM +0300, Jarkko Sakkinen wrote: > > > > > On Fri, Sep 18, 2020 at 04:53:37PM -0700, Sean Christopherson wrote: > > > > > > a noexec filesystem by loading code into an enclave, and to give the kernel the > > > > > > option of adding enclave specific LSM policies in the future. > > > > > > > > > > > > The source file (if one exists) for the enclave is long gone when the enclave > > > > > > is actually mmap()'d and mprotect()'d. To enforce noexec, the requested > > > > > > permissions for a given page are snapshotted when the page is added to the > > > > > > enclave, i.e. when the enclave is built. Enclave pages that will be executable > > > > > > must originate from an a MAYEXEC VMA, e.g. the source page can't come from a > > > > > > noexec file system. > > > > > > > > > > noexec check is done in __sgx_encl_add_page(), not in this callback. > > > > > sgx_vma_mprotect() calls sgx_encl_may_map(), which iterates the > > > > > addresses, checks that permissions are not surpassed and there are > > > > > no holes. > > > > > > > > Yes, that's what I said. > > > > > > sgx_encl_add_page() will remove such page. The callback does not > > > interact with this process as such pages never get to the enclave. > > > > I think we're in violent agreement, mostly. > > > > Userspace can add the page without EXEC permissions in the EPCM, and thus > > avoid the noexec/VM_MAYEXEC check. The enclave can then do EMODPE to gain > > EXEC permissions in the EPMC. Without the ->mprotect() hook, we wouldn't > > be able to detect/prevent such shenanigans. > > Right, the VM_MAYEXEC in the code is nested under VM_EXEC check. > > I'm only wondering why not block noexec completely with any permissions, > i.e. why not just have unconditional VM_MAYEXEC check? I.e. why not this: static int __sgx_encl_add_page(struct sgx_encl *encl, struct sgx_encl_page *encl_page, struct sgx_epc_page *epc_page, struct sgx_secinfo *secinfo, unsigned long src) { struct sgx_pageinfo pginfo; struct vm_area_struct *vma; struct page *src_page; int ret; vma = find_vma(current->mm, src); if (!vma) return -EFAULT; if (!(vma->vm_flags & VM_MAYEXEC)) return -EACCES; I'm not seeing the reason for "partial support" for noexec partitions. If there is a good reason, fine, let's just then document it. /Jarkko