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Thu, 24 Sep 2020 14:50:18 +0000 (UTC) IronPort-SDR: se4tpvvb8IDtpOOjsrn3jwQFwwKGEquMzPeSC13vrnFNCtoCbDrJTEAYxK7a2I/vidqoyVXomN hQnTBhHn9rnA== X-IronPort-AV: E=McAfee;i="6000,8403,9753"; a="148870490" X-IronPort-AV: E=Sophos;i="5.77,298,1596524400"; d="scan'208";a="148870490" X-Amp-Result: SKIPPED(no attachment in message) X-Amp-File-Uploaded: False Received: from fmsmga004.fm.intel.com ([10.253.24.48]) by orsmga101.jf.intel.com with ESMTP/TLS/ECDHE-RSA-AES256-GCM-SHA384; 24 Sep 2020 07:50:17 -0700 IronPort-SDR: uUNvx1tK2mR+DKUhznuzf+/VyzSw/BnL1LH6WFmk3ktTAgPcO0Dqvld7revry+oMEFvQWR9NnQ L2Unf7IyfyVg== X-IronPort-AV: E=Sophos;i="5.77,298,1596524400"; d="scan'208";a="336007847" Received: from rechen-mobl.amr.corp.intel.com (HELO [10.212.182.18]) ([10.212.182.18]) by fmsmga004-auth.fm.intel.com with ESMTP/TLS/ECDHE-RSA-AES256-GCM-SHA384; 24 Sep 2020 07:50:16 -0700 Subject: Re: [PATCH v38 10/24] mm: Add vm_ops->mprotect() To: Jarkko Sakkinen Cc: Andy Lutomirski , Sean Christopherson , 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, "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 References: <20200918235337.GA21189@sjchrist-ice> <1B23E216-0229-4BDD-8B09-807256A54AF5@amacapital.net> <20200922125801.GA133710@linux.intel.com> <25d46fdc-1c19-2de8-2ce8-1033a0027ecf@intel.com> <20200923143305.GE5160@linux.intel.com> From: Dave Hansen Autocrypt: addr=dave.hansen@intel.com; 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Linux x86_64; rv:68.0) Gecko/20100101 Thunderbird/68.10.0 MIME-Version: 1.0 In-Reply-To: <20200923143305.GE5160@linux.intel.com> Content-Type: text/plain; charset=utf-8 Content-Language: en-US Content-Transfer-Encoding: quoted-printable 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 9/23/20 7:33 AM, Jarkko Sakkinen wrote: > The consequence is that enclaves are best created with an ioctl API and= the > access control can be based only to the origin of the source file for t= he > enclave data, i.e. on VMA file pointer and page permissions. For exampl= e, > this could be done with LSM hooks that are triggered in the appropriate > ioctl's and they could make the access control decision based on this > information. >=20 > Unfortunately, there is ENCLS[EMODPE] that a running enclave can use to > upgrade its permissions. If we do not limit mmap() and mprotect(), encl= ave > could upgrade its permissions by using EMODPE followed by an appropriat= e > mprotect() call. This would be completely hidden from the kernel. >=20 > Add 'mprotect' hook to vm_ops, so that a callback can be implemeted for= SGX > that will ensure that {mmap, mprotect}() permissions do not surpass any= of > the original page permissions. This feature allows to maintain and refi= ne > sane access control for enclaves. Maybe I'm just being dense, but I still don't have a clear idea what function this hook serves. I understand that SGX has an orthogonal set of page permissions to the normal x86 page tables. It needs these so that the OS can't play nasty tricks on the enclave, like removing read-only protections that provide hardening. But, I still don't get the connection to mprotect() and the x86 paging permissions. If the enclave's permissions are orthogonal, then why bother with this hook? Why does the OS view of the enclave's memory matt= er?