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 X-Spam-Level: X-Spam-Status: No, score=-4.8 required=3.0 tests=BAYES_00,DKIMWL_WL_HIGH, DKIM_SIGNED,DKIM_VALID,DKIM_VALID_AU,MAILING_LIST_MULTI,SPF_HELO_NONE, SPF_PASS autolearn=no autolearn_force=no version=3.4.0 Received: from mail.kernel.org (mail.kernel.org [198.145.29.99]) by smtp.lore.kernel.org (Postfix) with ESMTP id 753ECC4727C for ; Tue, 29 Sep 2020 13:06:29 +0000 (UTC) Received: from vger.kernel.org (vger.kernel.org [23.128.96.18]) by mail.kernel.org (Postfix) with ESMTP id DBF52208FE for ; Tue, 29 Sep 2020 13:06:28 +0000 (UTC) DKIM-Signature: v=1; a=rsa-sha256; c=relaxed/simple; d=kernel.org; s=default; t=1601384789; bh=dKs40EB0zUNqF3k8hOXDHChpW1qE+Tc5ZCaCj+fNcAI=; h=Date:From:To:Cc:Subject:References:In-Reply-To:List-ID:From; b=1avJB8xQj9AQ9aHMAJMgTS6bsNiUTlOmhX69T4cKyZtR8Owbb1r/r2ZP09t1H+WaL 4k2hNadYEtM1EGTha1A5G1J8Wf/lb14C0YEr8EJ3xCgpm378IPiRqUFemlsC1DxY57 VO/sjjH7BfYUOa12B0Kfsco41ZaPB7e5qUzJJJxU= Received: (majordomo@vger.kernel.org) by vger.kernel.org via listexpand id S1728506AbgI2NGZ (ORCPT ); Tue, 29 Sep 2020 09:06:25 -0400 Received: from mail.kernel.org ([198.145.29.99]:48202 "EHLO mail.kernel.org" rhost-flags-OK-OK-OK-OK) by vger.kernel.org with ESMTP id S1728253AbgI2NGY (ORCPT ); Tue, 29 Sep 2020 09:06:24 -0400 Received: from kernel.org (unknown [87.71.73.56]) (using TLSv1.2 with cipher ECDHE-RSA-AES256-GCM-SHA384 (256/256 bits)) (No client certificate requested) by mail.kernel.org (Postfix) with ESMTPSA id 6DAC8207F7; Tue, 29 Sep 2020 13:06:08 +0000 (UTC) DKIM-Signature: v=1; a=rsa-sha256; c=relaxed/simple; d=kernel.org; s=default; t=1601384783; bh=dKs40EB0zUNqF3k8hOXDHChpW1qE+Tc5ZCaCj+fNcAI=; h=Date:From:To:Cc:Subject:References:In-Reply-To:From; b=kkoEdNeBwGUh5IVOWlI3TdmyaJCGl1uUtrsv4V7euPJfzeGsgVr9508rpCKlka84A TsDcDOdrDS9A4AaYCoyZ7lmCOsiredZMHpJsZ/ljNuc5atPQsZJCW42/ujWY54vc/A xHI6TcUVFoTK32LTlL0E1IvYKnm9SRUNQXn1aIps= Date: Tue, 29 Sep 2020 16:06:02 +0300 From: Mike Rapoport To: "Edgecombe, Rick P" Cc: "akpm@linux-foundation.org" , "tycho@tycho.ws" , "david@redhat.com" , "cl@linux.com" , "hpa@zytor.com" , "peterz@infradead.org" , "catalin.marinas@arm.com" , "linux-kselftest@vger.kernel.org" , "dave.hansen@linux.intel.com" , "will@kernel.org" , "linux-mm@kvack.org" , "idan.yaniv@ibm.com" , "kirill@shutemov.name" , "viro@zeniv.linux.org.uk" , "rppt@linux.ibm.com" , "linux-arch@vger.kernel.org" , "Williams, Dan J" , "bp@alien8.de" , "willy@infradead.org" , "luto@kernel.org" , "arnd@arndb.de" , "shuah@kernel.org" , "tglx@linutronix.de" , "linux-nvdimm@lists.01.org" , "linux-riscv@lists.infradead.org" , "x86@kernel.org" , "linux-arm-kernel@lists.infradead.org" , "linux-fsdevel@vger.kernel.org" , "Reshetova, Elena" , "palmer@dabbelt.com" , "mingo@redhat.com" , "mtk.manpages@gmail.com" , "linux-kernel@vger.kernel.org" , "linux-api@vger.kernel.org" , "jejb@linux.ibm.com" , "paul.walmsley@sifive.com" , "mark.rutland@arm.com" Subject: Re: [PATCH v6 3/6] mm: introduce memfd_secret system call to create "secret" memory areas Message-ID: <20200929130602.GF2142832@kernel.org> References: <20200924132904.1391-1-rppt@kernel.org> <20200924132904.1391-4-rppt@kernel.org> 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-api@vger.kernel.org On Tue, Sep 29, 2020 at 04:58:44AM +0000, Edgecombe, Rick P wrote: > On Thu, 2020-09-24 at 16:29 +0300, Mike Rapoport wrote: > > Introduce "memfd_secret" system call with the ability to create > > memory > > areas visible only in the context of the owning process and not > > mapped not > > only to other processes but in the kernel page tables as well. > > > > The user will create a file descriptor using the memfd_secret() > > system call > > where flags supplied as a parameter to this system call will define > > the > > desired protection mode for the memory associated with that file > > descriptor. > > > > Currently there are two protection modes: > > > > * exclusive - the memory area is unmapped from the kernel direct map > > and it > > is present only in the page tables of the owning mm. > > Seems like there were some concerns raised around direct map > efficiency, but in case you are going to rework this...how does this > memory work for the existing kernel functionality that does things like > this? > > get_user_pages(, &page); > ptr = kmap(page); > foo = *ptr; > > Not sure if I'm missing something, but I think apps could cause the > kernel to access a not-present page and oops. The idea is that this memory should not be accessible by the kernel, so the sequence you describe should indeed fail. Probably oops would be to noisy and in this case the report needs to be less verbose. -- Sincerely yours, Mike.