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Date:   Mon, 10 Jul 2023 11:53:40 +0200
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Subject: Re: [PATCH] kasan, slub: fix HW_TAGS zeroing with slub_debug
To:     andrey.konovalov@linux.dev, Marco Elver <elver@google.com>,
        Mark Rutland <mark.rutland@arm.com>
Cc:     Andrey Konovalov <andreyknvl@gmail.com>,
        Alexander Potapenko <glider@google.com>,
        Dmitry Vyukov <dvyukov@google.com>,
        Andrey Ryabinin <ryabinin.a.a@gmail.com>,
        Vincenzo Frascino <vincenzo.frascino@arm.com>,
        kasan-dev@googlegroups.com,
        Andrew Morton <akpm@linux-foundation.org>, linux-mm@kvack.org,
        Catalin Marinas <catalin.marinas@arm.com>,
        Peter Collingbourne <pcc@google.com>,
        Feng Tang <feng.tang@intel.com>, stable@vger.kernel.org,
        Christoph Lameter <cl@linux.com>,
        Pekka Enberg <penberg@kernel.org>,
        David Rientjes <rientjes@google.com>,
        Joonsoo Kim <iamjoonsoo.kim@lge.com>,
        Roman Gushchin <roman.gushchin@linux.dev>,
        Hyeonggon Yoo <42.hyeyoo@gmail.com>,
        linux-kernel@vger.kernel.org,
        Andrey Konovalov <andreyknvl@google.com>
References: <678ac92ab790dba9198f9ca14f405651b97c8502.1688561016.git.andreyknvl@google.com>
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From:   Vlastimil Babka <vbabka@suse.cz>
In-Reply-To: <678ac92ab790dba9198f9ca14f405651b97c8502.1688561016.git.andreyknvl@google.com>
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On 7/5/23 14:44, andrey.konovalov@linux.dev wrote:
> From: Andrey Konovalov <andreyknvl@google.com>
> 
> Commit 946fa0dbf2d8 ("mm/slub: extend redzone check to extra allocated
> kmalloc space than requested") added precise kmalloc redzone poisoning
> to the slub_debug functionality.
> 
> However, this commit didn't account for HW_TAGS KASAN fully initializing
> the object via its built-in memory initialization feature. Even though
> HW_TAGS KASAN memory initialization contains special memory initialization
> handling for when slub_debug is enabled, it does not account for in-object
> slub_debug redzones. As a result, HW_TAGS KASAN can overwrite these
> redzones and cause false-positive slub_debug reports.
> 
> To fix the issue, avoid HW_TAGS KASAN memory initialization when slub_debug
> is enabled altogether. Implement this by moving the __slub_debug_enabled
> check to slab_post_alloc_hook. Common slab code seems like a more
> appropriate place for a slub_debug check anyway.
> 
> Fixes: 946fa0dbf2d8 ("mm/slub: extend redzone check to extra allocated kmalloc space than requested")
> Cc: <stable@vger.kernel.org>
> Reported-by: Mark Rutland <mark.rutland@arm.com>
> Signed-off-by: Andrey Konovalov <andreyknvl@google.com>

Acked-by: Vlastimil Babka <vbabka@suse.cz>

Thanks!