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Howlett" , Vlastimil Babka , Mike Rapoport , Suren Baghdasaryan , Michal Hocko , Uladzislau Rezki , linux-arch@vger.kernel.org, linux-kernel@vger.kernel.org, linux-mm@kvack.org, Andrey Konovalov , Marco Elver , Vincenzo Frascino , Peter Collingbourne , Will Deacon , Ryan.Roberts@arm.com, david.hildenbrand@arm.com Subject: Re: [PATCH v2 2/3] kasan: skip HW tagging for all kernel thread stacks Message-ID: References: <20260324132631.482520-1-usama.anjum@arm.com> <20260324132631.482520-3-usama.anjum@arm.com> MIME-Version: 1.0 Content-Type: text/plain; charset=us-ascii Content-Disposition: inline In-Reply-To: X-Rspamd-Queue-Id: C6F0040003 X-Rspamd-Server: rspam07 X-Stat-Signature: ppn71wz1wcmkmtonwh7ntjmpidnyiykb X-Rspam-User: X-HE-Tag: 1776414679-755626 X-HE-Meta: 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 CzZgh6MR 1aKfFZ4qFXfdyZwWomuYWJQCKqxGZDThiiIk80wQ2QJ1uRFTkFmrUifwolnP5lkAPX584l13q/uqUgvC5JhSIwc1U5gAoylz1xNjwoEsx7sQPwA5N3Tl5y53Su9eycs/FBlj6/X1WXa24W8P3C5ycEBQitGnXDLsOs5WozrMEW/7WxB5tdlRdvMGUsaxcg8NqEDgEOvcr8Lw6WaT0wXnhVM8dQFmtvUSECwTHCvGT0fY2YBs= Sender: owner-linux-mm@kvack.org Precedence: bulk X-Loop: owner-majordomo@kvack.org List-ID: List-Subscribe: List-Unsubscribe: On Thu, Apr 16, 2026 at 11:03:46AM +0200, David Hildenbrand wrote: > On 4/10/26 20:36, Catalin Marinas wrote: > > On Fri, Apr 10, 2026 at 07:32:23PM +0100, Catalin Marinas wrote: > >> What the original approach might help with is use-after-realloc in case > >> we had a tagged pointer in a past life of a page and it still works now. > >> Oh well, that's I guess for other types of hardening to address like > >> delayed reallocation. > > > > Another thought (for a separate series) - we could try to map the stack > > as Untagged (unless stack tagging is enabled; needs compiler > > instrumentation) and enable canonical tag checking (newer addition to > > MTE). This way, any stray tagged pointer won't work on the stack since > > it needs a 0xf tag (canonical). > > Do you mean mapping it as Untagged in the vmap for CONFIG_VMAP_STACK or > also as Untagged in the directmap? > > The latter brings in the set of problems with direct map fragmentation. Just the vmap, there are a lot more problems with the direct map. Not sure how much it does in terms of security, maybe marginally. A match-all tag (0xf) would still be able to access the canonically tagged memory. -- Catalin