linux-kernel - Re: [PATCH v7 02/15] kasan: arm64: x86: Make special tags arch specific

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Message-ID: <aWEDDjQms8zbMgsB@wieczorr-mobl1.localdomain>
Date: Fri, 09 Jan 2026 13:37:49 +0000
From: Maciej Wieczor-Retman <m.wieczorretman@...me>
To: Will Deacon <will@...nel.org>
Cc: Andrey Ryabinin <ryabinin.a.a@...il.com>, Alexander Potapenko <glider@...gle.com>, Andrey Konovalov <andreyknvl@...il.com>, Dmitry Vyukov <dvyukov@...gle.com>, Vincenzo Frascino <vincenzo.frascino@....com>, Catalin Marinas <catalin.marinas@....com>, Thomas Gleixner <tglx@...utronix.de>, Ingo Molnar <mingo@...hat.com>, Borislav Petkov <bp@...en8.de>, Dave Hansen <dave.hansen@...ux.intel.com>, x86@...nel.org, "H. Peter Anvin" <hpa@...or.com>, Andrew Morton <akpm@...ux-foundation.org>, David Hildenbrand <david@...hat.com>, Lorenzo Stoakes <lorenzo.stoakes@...cle.com>, "Liam R. Howlett" <Liam.Howlett@...cle.com>, Vlastimil Babka <vbabka@...e.cz>, Mike Rapoport <rppt@...nel.org>, Suren Baghdasaryan <surenb@...gle.com>, Michal Hocko <mhocko@...e.com>, Samuel Holland <samuel.holland@...ive.com>, Maciej Wieczor-Retman <maciej.wieczor-retman@...el.com>, linux-kernel@...r.kernel.org, kasan-dev@...glegroups.com, linux-arm-kernel@...ts.infradead.org, linux-mm@...ck.org
Subject: Re: [PATCH v7 02/15] kasan: arm64: x86: Make special tags arch specific

Hi, and thanks for looking at the patches!

On 2026-01-08 at 17:56:39 +0000, Will Deacon wrote:
>On Wed, Dec 10, 2025 at 05:28:43PM +0000, Maciej Wieczor-Retman wrote:
>> From: Samuel Holland <samuel.holland@...ive.com>
...
>> +#ifdef CONFIG_KASAN_HW_TAGS
>> +#define KASAN_TAG_MIN		0xF0 /* minimum value for random tags */
>> +#define KASAN_TAG_WIDTH		4
>> +#else
>> +#define KASAN_TAG_WIDTH		8
>> +#endif
>
>Shouldn't this be 0 when KASAN is not in use at all?
>
>Will

This file (as well as the x86 version) gets included in
include/linux/kasan-tags.h:

	#if defined(CONFIG_KASAN_SW_TAGS) || defined(CONFIG_KASAN_HW_TAGS)
	#include <asm/kasan-tags.h>
	#endif

	#ifndef KASAN_TAG_WIDTH
	#define KASAN_TAG_WIDTH		0
	#endif

So the 8 or 4 value is only assigned if SW_TAGS or HW_TAGS are enabled.
Otherwise it's set to zero.

-- 
Kind regards
Maciej Wieczór-Retman