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X-OriginatorOrg: arm.com X-MS-Exchange-CrossTenant-OriginalArrivalTime: 06 May 2025 14:34:25.3081 (UTC) X-MS-Exchange-CrossTenant-Network-Message-Id: 894db330-e52b-46ea-c211-08dd8cab19a5 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: DB1PEPF000509E2.eurprd03.prod.outlook.com X-MS-Exchange-CrossTenant-AuthAs: Anonymous X-MS-Exchange-CrossTenant-FromEntityHeader: HybridOnPrem X-MS-Exchange-Transport-CrossTenantHeadersStamped: PAWPR08MB9495 Hi Peter, > On Fri, May 2, 2025 at 10:08 AM Catalin Marinas wrote: > > > > + Peter Collingbourne as he added the SA_EXPOSE_TAGBITS flag. > > > > On Thu, Apr 10, 2025 at 08:47:20AM +0100, Yeoreum Yun wrote: > > > Use the original FAR_EL1 value when an MTE tag check fault occurs, > > > if ARM64_MTE_FAR is supported. > > > This allows reports to include not only the logical tag (memory tag) > > > but also the address tag information. > > > > > > Applications that require this information should install a signal handler with > > > the SA_EXPOSE_TAGBITS flag. > > > While this introduces a minor ABI change, > > > most applications do not set this flag and therefore will not be affected. > > > > It is indeed a minor ABI in that a tag check fault resulting in a > > signal will report the bits 63:60 as well, not just 59:56 of the address > > (if the signal handler was registered with SA_EXPOSE_TAGBITS). > > > > I don't think user-space would notice but asking Peter. > > On Android we don't set bits 63:60 on heap addresses when MTE is > enabled (and userspace programs aren't allowed to modify them in > addresses they get back from the heap allocator either) so the fault > handler should continue to see them as 0. Of course, a userspace > program could be breaking the rules and setting those bits anyway, but > in that case it looks like the only consequence would be that the > error reports from the heap allocator would sometimes be missing some > information (and this could already happen if the access results in a > non-MTE fault) which I think is acceptable. > > Peter Thanks for your confirmation :) -- Sincerely, Yeoreum Yun