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Thu, 11 Mar 2021 16:28:38 +0000 Received: from mail.kernel.org ([198.145.29.99]) by desiato.infradead.org with esmtps (Exim 4.94 #2 (Red Hat Linux)) id 1lKOAl-009Zby-Ss for linux-arm-kernel@lists.infradead.org; Thu, 11 Mar 2021 16:28:35 +0000 Received: by mail.kernel.org (Postfix) with ESMTPSA id B875A64F9A; Thu, 11 Mar 2021 16:28:23 +0000 (UTC) Date: Thu, 11 Mar 2021 16:28:21 +0000 From: Catalin Marinas To: Vincenzo Frascino Cc: linux-arm-kernel@lists.infradead.org, linux-kernel@vger.kernel.org, kasan-dev@googlegroups.com, Andrew Morton , Will Deacon , Dmitry Vyukov , Andrey Ryabinin , Alexander Potapenko , Marco Elver , Evgenii Stepanov , Branislav Rankov , Andrey Konovalov , Lorenzo Pieralisi Subject: Re: [PATCH v14 8/8] kselftest/arm64: Verify that TCO is enabled in load_unaligned_zeropad() Message-ID: <20210311162820.GE30821@arm.com> References: <20210308161434.33424-1-vincenzo.frascino@arm.com> <20210308161434.33424-9-vincenzo.frascino@arm.com> <20210311132509.GB30821@arm.com> MIME-Version: 1.0 Content-Disposition: inline In-Reply-To: User-Agent: Mutt/1.10.1 (2018-07-13) X-CRM114-Version: 20100106-BlameMichelson ( TRE 0.8.0 (BSD) ) MR-646709E3 X-CRM114-CacheID: sfid-20210311_162828_722292_67F28DBB X-CRM114-Status: GOOD ( 29.51 ) X-BeenThere: linux-arm-kernel@lists.infradead.org X-Mailman-Version: 2.1.34 Precedence: list List-Id: List-Unsubscribe: , List-Archive: List-Post: List-Help: List-Subscribe: , 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 Thu, Mar 11, 2021 at 03:00:26PM +0000, Vincenzo Frascino wrote: > On 3/11/21 1:25 PM, Catalin Marinas wrote: > > On Mon, Mar 08, 2021 at 04:14:34PM +0000, Vincenzo Frascino wrote: > >> load_unaligned_zeropad() and __get/put_kernel_nofault() functions can > >> read passed some buffer limits which may include some MTE granule with a > >> different tag. > >> > >> When MTE async mode is enable, the load operation crosses the boundaries > >> and the next granule has a different tag the PE sets the TFSR_EL1.TF1 > >> bit as if an asynchronous tag fault is happened: > >> > >> ================================================================== > >> BUG: KASAN: invalid-access > >> Asynchronous mode enabled: no access details available > >> > >> CPU: 0 PID: 1 Comm: init Not tainted 5.12.0-rc1-ge1045c86620d-dirty #8 > >> Hardware name: FVP Base RevC (DT) > >> Call trace: > >> dump_backtrace+0x0/0x1c0 > >> show_stack+0x18/0x24 > >> dump_stack+0xcc/0x14c > >> kasan_report_async+0x54/0x70 > >> mte_check_tfsr_el1+0x48/0x4c > >> exit_to_user_mode+0x18/0x38 > >> finish_ret_to_user+0x4/0x15c > >> ================================================================== > >> > >> Verify that Tag Check Override (TCO) is enabled in these functions before > >> the load and disable it afterwards to prevent this to happen. > >> > >> Note: The issue has been observed only with an MTE enabled userspace. > > > > The above bug is all about kernel buffers. While userspace can trigger > > the relevant code paths, it should not matter whether the user has MTE > > enabled or not. Can you please confirm that you can still triggered the > > fault with kernel-mode MTE but non-MTE user-space? If not, we may have a > > bug somewhere as the two are unrelated: load_unaligned_zeropad() only > > acts on kernel buffers and are subject to the kernel MTE tag check fault > > mode. > > I retried and you are right, it does not matter if it is a MTE or non-MTE > user-space. The issue seems to be that this test does not trigger the problem > all the times which probably lead me to the wrong conclusions. Keep the test around for some quick checks before you get the kasan test support. > > I don't think we should have a user-space selftest for this. The bug is > > not about a user-kernel interface, so an in-kernel test is more > > appropriate. Could we instead add this to the kasan tests and calling > > load_unaligned_zeropad() and other functions directly? > > I agree with you we should abandon this strategy of triggering the issue due to > my comment above. I will investigate the option of having a kasan test and try > to come up with one that calls the relevant functions directly. I would prefer > though, since the rest of the series is almost ready, to post it in a future > series. What do you think? That's fine by me. -- Catalin _______________________________________________ linux-arm-kernel mailing list linux-arm-kernel@lists.infradead.org http://lists.infradead.org/mailman/listinfo/linux-arm-kernel