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Peter Anvin" , Andrew Morton , David Hildenbrand , Lorenzo Stoakes , "Liam R. Howlett" , Vlastimil Babka , Mike Rapoport , Suren Baghdasaryan , Michal Hocko , Samuel Holland , Maciej Wieczor-Retman , linux-kernel@vger.kernel.org, kasan-dev@googlegroups.com, linux-arm-kernel@lists.infradead.org, linux-mm@kvack.org Subject: Re: [PATCH v12 02/15] kasan: arm64: x86: Make special tags arch specific Message-ID: References: <6080be7964fc726327186d5bf7979e16ddd282bb.1774872838.git.m.wieczorretman@pm.me> MIME-Version: 1.0 Content-Type: text/plain; charset=us-ascii Content-Disposition: inline In-Reply-To: <6080be7964fc726327186d5bf7979e16ddd282bb.1774872838.git.m.wieczorretman@pm.me> X-Stat-Signature: yyi4mw5ikodasjrq795e6xmb4yj54xur X-Rspamd-Queue-Id: 47DD4180005 X-Rspam-User: X-Rspamd-Server: rspam10 X-HE-Tag: 1779820205-690643 X-HE-Meta: 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 rin+3ZBz qWQXDLOy9KabtWsWve4kdMX/BlviZlPUsXyEEEBvbP7UZy0lH5dfqk5h2J4zR44tw0TYNr7oyokGPQQ+WiS3Ea3YoV5omO1D91Nxw/g3EFJ+AmwChQcA/CE3Mq/VobKmpslsZpQ27mz4R3FKpQH73BxjsJ29oVOovPVG9HYLACwKcqXDdh9UD6tIQJsFXok/6kz/owpW/m81m17INOBxm4l7IZ5unIAMrEAlxsg+Goc5r2vyHkgFLlg2Hxu2SooSGEun28hLVHlzm6UDCldQTLV1p+yzMQQITM+rlBCiGLGHua8mnh6tLHCTrxCDpEaS8TVP0W1cpSvrXaNNLbe7Ho4thOW7aoA4SPb0E7xzbTyEtuXnIbySZsZab7vNqIrS5S2ebuS/y1W1hk1m7PYY3D9Ngklx6s7pLAlPpbAi0MerQ8DO8Y2kQaUQup/y5DX7cy4Mv/Q2ORunQiX5Mfg+liqFLHGLcowY1DDqaAgoPn4Zuw3Y= Sender: owner-linux-mm@kvack.org Precedence: bulk X-Loop: owner-majordomo@kvack.org List-ID: List-Subscribe: List-Unsubscribe: On Mon, Mar 30, 2026 at 02:33:16PM +0000, Maciej Wieczor-Retman wrote: > From: Samuel Holland > > KASAN's tag-based mode defines multiple special tag values. They're > reserved for: > - Native kernel value. On arm64 it's 0xFF and it causes an early return > in the tag checking function. > - Invalid value. 0xFE marks an area as freed / unallocated. It's also > the value that is used to initialize regions of shadow memory. > - Min and max values. 0xFD is the highest value that can be randomly > generated for a new tag. 0 is the minimal value with the exception of > arm64's hardware mode where it is equal to 0xF0. > > Metadata macro is also defined: > - Tag width equal to 8. > > Tag-based mode on x86 is going to use 4 bit wide tags so all the above > values need to be changed accordingly. > > Make tag width and native kernel tag arch specific for x86 and arm64. > > Base the invalid tag value and the max value on the native kernel tag > since they follow the same pattern on both mentioned architectures. > > Also generalize KASAN_SHADOW_INIT and 0xff used in various > page_kasan_tag* helpers. > > Give KASAN_TAG_MIN the default value of zero, and move the special value > for hw_tags arm64 to its arch specific kasan-tags.h. > > Signed-off-by: Samuel Holland > Co-developed-by: Maciej Wieczor-Retman > Signed-off-by: Maciej Wieczor-Retman > Acked-by: Will Deacon (for the arm part) > Reviewed-by: Andrey Konovalov > Reviewed-by: Andrey Ryabinin Acked-by: Catalin Marinas