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Fri, 16 Jan 2026 05:33:35 -0800 (PST) Message-ID: Date: Fri, 16 Jan 2026 14:32:49 +0100 MIME-Version: 1.0 User-Agent: Mozilla Thunderbird Subject: Re: [PATCH v8 02/14] kasan: arm64: x86: Make special tags arch specific To: Maciej Wieczor-Retman , Alexander Potapenko , Andrey Konovalov , Dmitry Vyukov , Vincenzo Frascino , Catalin Marinas , Will Deacon , Thomas Gleixner , Ingo Molnar , Borislav Petkov , Dave Hansen , x86@kernel.org, "H. Peter Anvin" , Andrew Morton , David Hildenbrand , Lorenzo Stoakes , "Liam R. Howlett" , Vlastimil Babka , Mike Rapoport , Suren Baghdasaryan , Michal Hocko Cc: Samuel Holland , Maciej Wieczor-Retman , linux-kernel@vger.kernel.org, kasan-dev@googlegroups.com, linux-arm-kernel@lists.infradead.org, linux-mm@kvack.org References: Content-Language: en-US From: Andrey Ryabinin In-Reply-To: Content-Type: text/plain; charset=UTF-8 Content-Transfer-Encoding: 7bit X-Stat-Signature: ng1haxp8sf6e743x18exzb61jjjampj1 X-Rspamd-Queue-Id: 4922516000E X-Rspam-User: X-Rspamd-Server: rspam02 X-HE-Tag: 1768570418-812620 X-HE-Meta: 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 CiI9k/pa 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 X-Bogosity: Ham, tests=bogofilter, spamicity=0.000000, version=1.2.4 Sender: owner-linux-mm@kvack.org Precedence: bulk X-Loop: owner-majordomo@kvack.org List-ID: List-Subscribe: List-Unsubscribe: On 1/12/26 6:27 PM, 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 Ryabinin