From nobody Sun Apr 5 16:31:09 2026 Received: from foss.arm.com (foss.arm.com [217.140.110.172]) by smtp.subspace.kernel.org (Postfix) with ESMTP id C2AED3F99C9; Tue, 24 Mar 2026 13:26:58 +0000 (UTC) Authentication-Results: smtp.subspace.kernel.org; arc=none smtp.client-ip=217.140.110.172 ARC-Seal: i=1; a=rsa-sha256; d=subspace.kernel.org; s=arc-20240116; t=1774358821; cv=none; b=RQt8HHglZXw5wPSYYHfdrN/1eVUr+JnE+pkzLNttO4ncbtKpcGhHqI4juX02F+NEC7psB1DyCeGQA0VCF14Vw9BwZzDqgbBGfLUxXK6PDoD/v0gsaEzVcp0tqqTXoZj7B7E/5vq57W3jlUa4YyrCPhU4KcX7yk5IP+AygdNWiEA= ARC-Message-Signature: i=1; a=rsa-sha256; d=subspace.kernel.org; s=arc-20240116; t=1774358821; c=relaxed/simple; bh=VhBd0SXQdStB06Ok11/K+KdOFOf0X6cWYTl++e9UdAc=; h=From:To:Cc:Subject:Date:Message-ID:In-Reply-To:References: MIME-Version; b=AQhHHTwiBOBsb7/JRAjA2LQazKwUKrguP9PaqTCZe8An/rt517uC2ckMiBkm1nGxhJFL8Zn+Ec52kqYJBLaU0ao871tXkG9mq2Spd4oHjFElFt4oSmNYfhtcjnNb0X962MR40EHf7foB7PT6IRNiGH9dXsWEsOcX+MZgacNrpWg= ARC-Authentication-Results: i=1; smtp.subspace.kernel.org; dmarc=pass (p=none dis=none) header.from=arm.com; spf=pass smtp.mailfrom=arm.com; dkim=pass (1024-bit key) header.d=arm.com header.i=@arm.com header.b=Lay9mLSy; arc=none smtp.client-ip=217.140.110.172 Authentication-Results: smtp.subspace.kernel.org; dmarc=pass (p=none dis=none) header.from=arm.com Authentication-Results: smtp.subspace.kernel.org; spf=pass smtp.mailfrom=arm.com Authentication-Results: smtp.subspace.kernel.org; dkim=pass (1024-bit key) header.d=arm.com header.i=@arm.com header.b="Lay9mLSy" Received: from usa-sjc-imap-foss1.foss.arm.com (unknown [10.121.207.14]) by usa-sjc-mx-foss1.foss.arm.com (Postfix) with ESMTP id 10331153B; Tue, 24 Mar 2026 06:26:52 -0700 (PDT) Received: from e142334-100.cambridge.arm.com (e142334-100.cambridge.arm.com [10.1.194.63]) by usa-sjc-imap-foss1.foss.arm.com (Postfix) with ESMTPA id BD88D3FAF5; Tue, 24 Mar 2026 06:26:53 -0700 (PDT) DKIM-Signature: v=1; a=rsa-sha256; c=simple/simple; d=arm.com; s=foss; t=1774358818; bh=VhBd0SXQdStB06Ok11/K+KdOFOf0X6cWYTl++e9UdAc=; h=From:To:Cc:Subject:Date:In-Reply-To:References:From; b=Lay9mLSy/mKrnA78g3qAMj48V6DZbVTZSKlQxfMcJT4P58/f6HDrxW5nnkZWA7i8v N4bdPcm3lyqUJky+4QOxQgv/m7/DvVhfe7M0UEBh86twBM/C8F7Ld4W4yjKhXniipe nOYfehEH0YKbdvhLs6jdw2/ti3BtLFWLvp1/FCCE= From: Muhammad Usama Anjum To: Arnd Bergmann , Ingo Molnar , Peter Zijlstra , Juri Lelli , Vincent Guittot , Dietmar Eggemann , Steven Rostedt , Ben Segall , Mel Gorman , Valentin Schneider , Kees Cook , Andrew Morton , David Hildenbrand , Lorenzo Stoakes , "Liam R. 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 , Catalin Marinas , Will Deacon , Ryan.Roberts@arm.com, david.hildenbrand@arm.com Cc: Muhammad Usama Anjum Subject: [PATCH v2 2/3] kasan: skip HW tagging for all kernel thread stacks Date: Tue, 24 Mar 2026 13:26:28 +0000 Message-ID: <20260324132631.482520-3-usama.anjum@arm.com> X-Mailer: git-send-email 2.47.3 In-Reply-To: <20260324132631.482520-1-usama.anjum@arm.com> References: <20260324132631.482520-1-usama.anjum@arm.com> Precedence: bulk X-Mailing-List: linux-kernel@vger.kernel.org List-Id: List-Subscribe: List-Unsubscribe: MIME-Version: 1.0 Content-Transfer-Encoding: quoted-printable Content-Type: text/plain; charset="utf-8" HW-tag KASAN never checks kernel stacks because stack pointers carry the match-all tag, so setting/poisoning tags is pure overhead. - Add __GFP_SKIP_KASAN to THREADINFO_GFP so every stack allocator that uses it skips tagging (fork path plus arch users) - Add __GFP_SKIP_KASAN to GFP_VMAP_STACK for the fork-specific vmap stacks. - When reusing cached vmap stacks, skip kasan_unpoison_range() if HW tags are enabled. Software KASAN is unchanged; this only affects tag-based KASAN. Signed-off-by: Muhammad Usama Anjum --- Changes since v1: - Specify _GFP_SKIP_KASAN in THREADINFO_GFP and GFP_VMAP_STACK to use it everywhere and cover the missed locations - Update description --- include/linux/thread_info.h | 2 +- kernel/fork.c | 5 +++-- 2 files changed, 4 insertions(+), 3 deletions(-) diff --git a/include/linux/thread_info.h b/include/linux/thread_info.h index 051e429026904..307b8390fc670 100644 --- a/include/linux/thread_info.h +++ b/include/linux/thread_info.h @@ -92,7 +92,7 @@ static inline long set_restart_fn(struct restart_block *r= estart, #define THREAD_ALIGN THREAD_SIZE #endif =20 -#define THREADINFO_GFP (GFP_KERNEL_ACCOUNT | __GFP_ZERO) +#define THREADINFO_GFP (GFP_KERNEL_ACCOUNT | __GFP_ZERO | __GFP_SKIP_KASA= N) =20 /* * flag set/clear/test wrappers diff --git a/kernel/fork.c b/kernel/fork.c index bb0c2613a5604..4bc7a03662109 100644 --- a/kernel/fork.c +++ b/kernel/fork.c @@ -207,7 +207,7 @@ static DEFINE_PER_CPU(struct vm_struct *, cached_stacks= [NR_CACHED_STACKS]); * accounting is performed by the code assigning/releasing stacks to tasks. * We need a zeroed memory without __GFP_ACCOUNT. */ -#define GFP_VMAP_STACK (GFP_KERNEL | __GFP_ZERO) +#define GFP_VMAP_STACK (GFP_KERNEL | __GFP_ZERO | __GFP_SKIP_KASAN) =20 struct vm_stack { struct rcu_head rcu; @@ -345,7 +345,8 @@ static int alloc_thread_stack_node(struct task_struct *= tsk, int node) } =20 /* Reset stack metadata. */ - kasan_unpoison_range(vm_area->addr, THREAD_SIZE); + if (!kasan_hw_tags_enabled()) + kasan_unpoison_range(vm_area->addr, THREAD_SIZE); =20 stack =3D kasan_reset_tag(vm_area->addr); =20 --=20 2.47.3