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X-OriginatorOrg: arm.com X-MS-Exchange-CrossTenant-OriginalArrivalTime: 19 Aug 2025 15:15:59.0649 (UTC) X-MS-Exchange-CrossTenant-Network-Message-Id: 6a3a1757-0bcf-4349-ce77-08dddf334d6b X-MS-Exchange-CrossTenant-Id: f34e5979-57d9-4aaa-ad4d-b122a662184d X-MS-Exchange-CrossTenant-OriginalAttributedTenantConnectingIp: TenantId=f34e5979-57d9-4aaa-ad4d-b122a662184d;Ip=[4.158.2.129];Helo=[outbound-uk1.az.dlp.m.darktrace.com] X-MS-Exchange-CrossTenant-AuthSource: DB5PEPF00014B8C.eurprd02.prod.outlook.com X-MS-Exchange-CrossTenant-AuthAs: Anonymous X-MS-Exchange-CrossTenant-FromEntityHeader: HybridOnPrem X-MS-Exchange-Transport-CrossTenantHeadersStamped: PAVPR08MB9506 X-CRM114-Version: 20100106-BlameMichelson ( TRE 0.8.0 (BSD) ) MR-646709E3 X-CRM114-CacheID: sfid-20250819_081607_929870_96032679 X-CRM114-Status: GOOD ( 20.15 ) 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: , Sender: "linux-arm-kernel" Errors-To: linux-arm-kernel-bounces+linux-arm-kernel=archiver.kernel.org@lists.infradead.org > > > > > > why we need to care about the different settings for tag checking when > > > > > > we use uaccess_disable_privileged()? > > > [...] > > > > > > But, although tag check fault happens in kernel side, > > > > > > It seems to be handled by fixup code if user address is wrong. > > > > > > > > > > The user may know it is wrong and not care (e.g. one wants to keep using > > > > > a buggy application). > > > > > > > > Then Does this example -- ignoring wrong and keep using a buggy > > > > application shows us that we need to enable TCO when > > > > we runs the LSUI instruction? > > > > > > > > AFAIK, LSUI instruction also check memory tag -- i.e) ldtadd. > > > > if passed user address which has unmatched tag and if user isn't > > > > interested in tah check, It can meet the unexpected report from KASAN. > > > > > > That's a valid point w.r.t. PSTATE.TCO that applies to copy_to/from_user > > > as well. I don't think we documented it but we don't expect the user > > > PSTATE.TCO state to be taken into account while doing uaccess from the > > > kernel. We do, however, expect SCTLR_EL1.TCF0 to be honoured and that's > > > what the user normally tweaks via a prctl(). The TCO is meant to > > > disable tag checking briefly when TCF enabled the tag check faults. > > > > So, IMHO, as copy_to/from_user (ldt/sttr) enable tco before it operates, > > They don't enable TCO. Ah right. I've confused. Thanks for answer! > > -- > Catalin -- Sincerely, Yeoreum Yun