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Archived-At: List-Archive: List-Help: List-Post: List-Subscribe: List-Unsubscribe: Content-Type: text/plain; charset="us-ascii" Content-Transfer-Encoding: 7bit On Tue, 2020-09-29 at 16:06 +0300, Mike Rapoport wrote: > 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. I was more concerned that it could cause kernel instabilities. I see, so it should not be accessed even at the userspace address? I wonder if it should be prevented somehow then. At least get_user_pages() should be prevented I think. Blocking copy_*_user() access might not be simple. I'm also not so sure that a user would never have any possible reason to copy data from this memory into the kernel, even if it's just convenience. In which case a user setup could break if a specific kernel implementation switched to get_user_pages()/kmap() from using copy_*_user(). So seems maybe a bit thorny without fully blocking access from the kernel, or deprecating that pattern. You should probably call out these "no passing data to/from the kernel" expectations, unless I missed them somewhere. _______________________________________________ Linux-nvdimm mailing list -- linux-nvdimm@lists.01.org To unsubscribe send an email to linux-nvdimm-leave@lists.01.org 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=-3.8 required=3.0 tests=BAYES_00,DKIM_SIGNED, DKIM_VALID,HEADER_FROM_DIFFERENT_DOMAINS,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 BBBE7C4727F for ; Tue, 29 Sep 2020 20:06:09 +0000 (UTC) Received: from vger.kernel.org (vger.kernel.org [23.128.96.18]) by mail.kernel.org (Postfix) with ESMTP id 3B1042076A for ; Tue, 29 Sep 2020 20:06:09 +0000 (UTC) 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"shuah@kernel.org" , "arnd@arndb.de" , "tglx@linutronix.de" , "linux-nvdimm@lists.01.org" , "x86@kernel.org" , "linux-riscv@lists.infradead.org" , "linux-arm-kernel@lists.infradead.org" , "Reshetova, Elena" , "palmer@dabbelt.com" , "linux-fsdevel@vger.kernel.org" , "mingo@redhat.com" , "mtk.manpages@gmail.com" , "tycho@tycho.ws" , "linux-api@vger.kernel.org" , "linux-kernel@vger.kernel.org" , "paul.walmsley@sifive.com" , "jejb@linux.ibm.com" Subject: Re: [PATCH v6 3/6] mm: introduce memfd_secret system call to create "secret" memory areas Thread-Topic: [PATCH v6 3/6] mm: introduce memfd_secret system call to create "secret" memory areas Thread-Index: AQHWlh00WOVRjW6Kw0OmwswTJieWmql/llUAgAB1WIA= Date: Tue, 29 Sep 2020 20:06:03 +0000 Message-ID: <839fbb26254dc9932dcff3c48a3a4ab038c016ea.camel@intel.com> References: <20200924132904.1391-1-rppt@kernel.org> <20200924132904.1391-4-rppt@kernel.org> <20200929130602.GF2142832@kernel.org> In-Reply-To: <20200929130602.GF2142832@kernel.org> 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X-MS-Exchange-CrossTenant-originalarrivaltime: 29 Sep 2020 20:06:03.2431 (UTC) X-MS-Exchange-CrossTenant-fromentityheader: Hosted X-MS-Exchange-CrossTenant-id: 46c98d88-e344-4ed4-8496-4ed7712e255d X-MS-Exchange-CrossTenant-mailboxtype: HOSTED X-MS-Exchange-CrossTenant-userprincipalname: qerPx6uvSfiDlNkAn28LFar8dqkVT0D7PYtTQX37E+jOeHFUu4i91ljcPYyoeqKxGuWJQtakG92lFFpNSzrUBDA8Y8loSYskpx9SPDS4p1I= X-MS-Exchange-Transport-CrossTenantHeadersStamped: SA0PR11MB4557 X-OriginatorOrg: intel.com X-CRM114-Version: 20100106-BlameMichelson ( TRE 0.8.0 (BSD) ) MR-646709E3 X-CRM114-CacheID: sfid-20200929_160608_772675_F02A9DC4 X-CRM114-Status: GOOD ( 31.95 ) X-BeenThere: linux-riscv@lists.infradead.org X-Mailman-Version: 2.1.29 Precedence: list List-Id: List-Unsubscribe: , List-Archive: List-Post: List-Help: List-Subscribe: , Cc: "mark.rutland@arm.com" , "david@redhat.com" , "peterz@infradead.org" , "catalin.marinas@arm.com" , "dave.hansen@linux.intel.com" , "linux-mm@kvack.org" , "linux-kselftest@vger.kernel.org" , "hpa@zytor.com" , "cl@linux.com" , "shuah@kernel.org" , "tglx@linutronix.de" , "Reshetova, Elena" , "linux-arch@vger.kernel.org" , "tycho@tycho.ws" , "arnd@arndb.de" , "linux-nvdimm@lists.01.org" , "idan.yaniv@ibm.com" , "x86@kernel.org" , "willy@infradead.org" , "rppt@linux.ibm.com" , "mingo@redhat.com" , "mtk.manpages@gmail.com" , "will@kernel.org" , "jejb@linux.ibm.com" , "bp@alien8.de" , "viro@zeniv.linux.org.uk" , "luto@kernel.org" , "paul.walmsley@sifive.com" , "kirill@shutemov.name" , "Williams, Dan J" , "linux-arm-kernel@lists.infradead.org" , "linux-api@vger.kernel.org" , "linux-kernel@vger.kernel.org" , "linux-riscv@lists.infradead.org" , "palmer@dabbelt.com" , "linux-fsdevel@vger.kernel.org" , "akpm@linux-foundation.org" Content-Type: text/plain; charset="us-ascii" Content-Transfer-Encoding: 7bit Sender: "linux-riscv" Errors-To: linux-riscv-bounces+linux-riscv=archiver.kernel.org@lists.infradead.org On Tue, 2020-09-29 at 16:06 +0300, Mike Rapoport wrote: > 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. I was more concerned that it could cause kernel instabilities. I see, so it should not be accessed even at the userspace address? I wonder if it should be prevented somehow then. At least get_user_pages() should be prevented I think. Blocking copy_*_user() access might not be simple. I'm also not so sure that a user would never have any possible reason to copy data from this memory into the kernel, even if it's just convenience. In which case a user setup could break if a specific kernel implementation switched to get_user_pages()/kmap() from using copy_*_user(). So seems maybe a bit thorny without fully blocking access from the kernel, or deprecating that pattern. You should probably call out these "no passing data to/from the kernel" expectations, unless I missed them somewhere. _______________________________________________ linux-riscv mailing list linux-riscv@lists.infradead.org http://lists.infradead.org/mailman/listinfo/linux-riscv 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=-3.8 required=3.0 tests=BAYES_00,DKIM_SIGNED, DKIM_VALID,HEADER_FROM_DIFFERENT_DOMAINS,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 BB3B6C47426 for ; Tue, 29 Sep 2020 20:06:12 +0000 (UTC) Received: from kanga.kvack.org (kanga.kvack.org [205.233.56.17]) by mail.kernel.org (Postfix) with ESMTP id 01D8820848 for ; Tue, 29 Sep 2020 20:06:11 +0000 (UTC) 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"shuah@kernel.org" , "arnd@arndb.de" , "tglx@linutronix.de" , "linux-nvdimm@lists.01.org" , "x86@kernel.org" , "linux-riscv@lists.infradead.org" , "linux-arm-kernel@lists.infradead.org" , "Reshetova, Elena" , "palmer@dabbelt.com" , "linux-fsdevel@vger.kernel.org" , "mingo@redhat.com" , "mtk.manpages@gmail.com" , "tycho@tycho.ws" , "linux-api@vger.kernel.org" , "linux-kernel@vger.kernel.org" , "paul.walmsley@sifive.com" , "jejb@linux.ibm.com" Subject: Re: [PATCH v6 3/6] mm: introduce memfd_secret system call to create "secret" memory areas Thread-Topic: [PATCH v6 3/6] mm: introduce memfd_secret system call to create "secret" memory areas Thread-Index: AQHWlh00WOVRjW6Kw0OmwswTJieWmql/llUAgAB1WIA= Date: Tue, 29 Sep 2020 20:06:03 +0000 Message-ID: <839fbb26254dc9932dcff3c48a3a4ab038c016ea.camel@intel.com> References: <20200924132904.1391-1-rppt@kernel.org> <20200924132904.1391-4-rppt@kernel.org> <20200929130602.GF2142832@kernel.org> In-Reply-To: <20200929130602.GF2142832@kernel.org> 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X-MS-Exchange-CrossTenant-originalarrivaltime: 29 Sep 2020 20:06:03.2431 (UTC) X-MS-Exchange-CrossTenant-fromentityheader: Hosted X-MS-Exchange-CrossTenant-id: 46c98d88-e344-4ed4-8496-4ed7712e255d X-MS-Exchange-CrossTenant-mailboxtype: HOSTED X-MS-Exchange-CrossTenant-userprincipalname: qerPx6uvSfiDlNkAn28LFar8dqkVT0D7PYtTQX37E+jOeHFUu4i91ljcPYyoeqKxGuWJQtakG92lFFpNSzrUBDA8Y8loSYskpx9SPDS4p1I= X-MS-Exchange-Transport-CrossTenantHeadersStamped: SA0PR11MB4557 X-OriginatorOrg: intel.com X-CRM114-Version: 20100106-BlameMichelson ( TRE 0.8.0 (BSD) ) MR-646709E3 X-CRM114-CacheID: sfid-20200929_160608_772675_F02A9DC4 X-CRM114-Status: GOOD ( 31.95 ) X-BeenThere: linux-arm-kernel@lists.infradead.org X-Mailman-Version: 2.1.29 Precedence: list List-Id: List-Unsubscribe: , List-Archive: List-Post: List-Help: List-Subscribe: , Cc: "mark.rutland@arm.com" , "david@redhat.com" , "peterz@infradead.org" , "catalin.marinas@arm.com" , "dave.hansen@linux.intel.com" , "linux-mm@kvack.org" , "linux-kselftest@vger.kernel.org" , "hpa@zytor.com" , "cl@linux.com" , "shuah@kernel.org" , "tglx@linutronix.de" , "Reshetova, Elena" , "linux-arch@vger.kernel.org" , "tycho@tycho.ws" , "arnd@arndb.de" , "linux-nvdimm@lists.01.org" , "idan.yaniv@ibm.com" , "x86@kernel.org" , "willy@infradead.org" , "rppt@linux.ibm.com" , "mingo@redhat.com" , "mtk.manpages@gmail.com" , "will@kernel.org" , "jejb@linux.ibm.com" , "bp@alien8.de" , "viro@zeniv.linux.org.uk" , "luto@kernel.org" , "paul.walmsley@sifive.com" , "kirill@shutemov.name" , "Williams, Dan J" , "linux-arm-kernel@lists.infradead.org" , "linux-api@vger.kernel.org" , "linux-kernel@vger.kernel.org" , "linux-riscv@lists.infradead.org" , "palmer@dabbelt.com" , "linux-fsdevel@vger.kernel.org" , "akpm@linux-foundation.org" Content-Type: text/plain; charset="us-ascii" Content-Transfer-Encoding: 7bit Sender: "linux-arm-kernel" Errors-To: linux-arm-kernel-bounces+linux-arm-kernel=archiver.kernel.org@lists.infradead.org On Tue, 2020-09-29 at 16:06 +0300, Mike Rapoport wrote: > 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. I was more concerned that it could cause kernel instabilities. I see, so it should not be accessed even at the userspace address? I wonder if it should be prevented somehow then. At least get_user_pages() should be prevented I think. Blocking copy_*_user() access might not be simple. I'm also not so sure that a user would never have any possible reason to copy data from this memory into the kernel, even if it's just convenience. In which case a user setup could break if a specific kernel implementation switched to get_user_pages()/kmap() from using copy_*_user(). So seems maybe a bit thorny without fully blocking access from the kernel, or deprecating that pattern. You should probably call out these "no passing data to/from the kernel" expectations, unless I missed them somewhere. _______________________________________________ linux-arm-kernel mailing list linux-arm-kernel@lists.infradead.org http://lists.infradead.org/mailman/listinfo/linux-arm-kernel