From: Andrew Morton <akpm@linux-foundation.org>
To: Muhammad Usama Anjum <usama.anjum@arm.com>
Cc: Arnd Bergmann <arnd@arndb.de>, Ingo Molnar <mingo@redhat.com>,
Peter Zijlstra <peterz@infradead.org>,
Juri Lelli <juri.lelli@redhat.com>,
Vincent Guittot <vincent.guittot@linaro.org>,
Dietmar Eggemann <dietmar.eggemann@arm.com>,
Steven Rostedt <rostedt@goodmis.org>,
Ben Segall <bsegall@google.com>, Mel Gorman <mgorman@suse.de>,
Valentin Schneider <vschneid@redhat.com>,
Kees Cook <kees@kernel.org>, David Hildenbrand <david@kernel.org>,
Lorenzo Stoakes <ljs@kernel.org>,
"Liam R. Howlett" <Liam.Howlett@oracle.com>,
Vlastimil Babka <vbabka@kernel.org>,
Mike Rapoport <rppt@kernel.org>,
Suren Baghdasaryan <surenb@google.com>,
Michal Hocko <mhocko@suse.com>,
Uladzislau Rezki <urezki@gmail.com>,
linux-arch@vger.kernel.org, linux-kernel@vger.kernel.org,
linux-mm@kvack.org, Andrey Konovalov <andreyknvl@gmail.com>,
Marco Elver <elver@google.com>,
Vincenzo Frascino <vincenzo.frascino@arm.com>,
Peter Collingbourne <pcc@google.com>,
Catalin Marinas <catalin.marinas@arm.com>,
Will Deacon <will@kernel.org>,
Ryan.Roberts@arm.com, david.hildenbrand@arm.com
Subject: Re: [PATCH 0/3] KASAN: HW_TAGS: Disable tagging for stack and page-tables
Date: Thu, 19 Mar 2026 20:10:57 -0700 [thread overview]
Message-ID: <20260319201057.05d57006408a2f77342eedc2@linux-foundation.org> (raw)
In-Reply-To: <20260319114952.3241359-1-usama.anjum@arm.com>
On Thu, 19 Mar 2026 11:49:43 +0000 Muhammad Usama Anjum <usama.anjum@arm.com> wrote:
> Stacks and page tables are always accessed with the match‑all tag,
> so assigning a new random tag every time at allocation and setting
> invalid tag at deallocation time, just adds overhead without improving
> the detection.
>
> With __GFP_SKIP_KASAN the page keeps its poison tag and KASAN_TAG_KERNEL
> (match-all tag) is stored in the page flags while keeping the poison tag
> in the hardware. The benefit of it is that 256 tag setting instruction
> per 4 kB page aren't needed at allocation and deallocation time.
>
> Thus match‑all pointers still work, while non‑match tags (other than
> poison tag) still fault.
>
> __GFP_SKIP_KASAN only skips for KASAN_HW_TAGS mode, so coverage is
> unchanged.
>
Some questions from Sashiko:
https://sashiko.dev/#/patchset/20260319114952.3241359-1-usama.anjum%40arm.com
next prev parent reply other threads:[~2026-03-20 3:11 UTC|newest]
Thread overview: 14+ messages / expand[flat|nested] mbox.gz Atom feed top
2026-03-19 11:49 [PATCH 0/3] KASAN: HW_TAGS: Disable tagging for stack and page-tables Muhammad Usama Anjum
2026-03-19 11:49 ` [PATCH 1/3] vmalloc: add __GFP_SKIP_KASAN support Muhammad Usama Anjum
2026-03-19 12:22 ` Ryan Roberts
2026-03-19 12:57 ` Muhammad Usama Anjum
2026-03-19 11:49 ` [PATCH 2/3] fork: skip MTE tagging for kernel stacks Muhammad Usama Anjum
2026-03-19 12:09 ` Ryan Roberts
2026-03-19 12:29 ` Muhammad Usama Anjum
2026-03-19 11:49 ` [PATCH 3/3] mm: SKIP KASAN for page table allocations Muhammad Usama Anjum
2026-03-19 12:09 ` Ryan Roberts
2026-03-20 3:10 ` Andrew Morton [this message]
2026-03-23 14:53 ` [PATCH 0/3] KASAN: HW_TAGS: Disable tagging for stack and page-tables Muhammad Usama Anjum
2026-03-20 8:53 ` David Hildenbrand (Arm)
2026-03-23 15:06 ` Muhammad Usama Anjum
2026-03-26 13:40 ` David Hildenbrand (Arm)
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