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Date: Thu, 17 Sep 2020 11:47:59 +0200 From: Alexander Potapenko <glider@...gle.com> To: Christopher Lameter <cl@...ux.com> Cc: Marco Elver <elver@...gle.com>, Andrew Morton <akpm@...ux-foundation.org>, "H. Peter Anvin" <hpa@...or.com>, "Paul E. McKenney" <paulmck@...nel.org>, Andrey Konovalov <andreyknvl@...gle.com>, Andrey Ryabinin <aryabinin@...tuozzo.com>, Andy Lutomirski <luto@...nel.org>, Borislav Petkov <bp@...en8.de>, Catalin Marinas <catalin.marinas@....com>, Dave Hansen <dave.hansen@...ux.intel.com>, David Rientjes <rientjes@...gle.com>, Dmitriy Vyukov <dvyukov@...gle.com>, Eric Dumazet <edumazet@...gle.com>, Greg Kroah-Hartman <gregkh@...uxfoundation.org>, Ingo Molnar <mingo@...hat.com>, Jann Horn <jannh@...gle.com>, Jonathan.Cameron@...wei.com, Jonathan Corbet <corbet@....net>, Joonsoo Kim <iamjoonsoo.kim@....com>, Kees Cook <keescook@...omium.org>, Mark Rutland <mark.rutland@....com>, Pekka Enberg <penberg@...nel.org>, Peter Zijlstra <peterz@...radead.org>, Qian Cai <cai@....pw>, Thomas Gleixner <tglx@...utronix.de>, Vlastimil Babka <vbabka@...e.cz>, Will Deacon <will@...nel.org>, "the arch/x86 maintainers" <x86@...nel.org>, "open list:DOCUMENTATION" <linux-doc@...r.kernel.org>, LKML <linux-kernel@...r.kernel.org>, kasan-dev <kasan-dev@...glegroups.com>, Linux ARM <linux-arm-kernel@...ts.infradead.org>, Linux Memory Management List <linux-mm@...ck.org> Subject: Re: [PATCH v2 04/10] mm, kfence: insert KFENCE hooks for SLAB > > static __always_inline void * > > -slab_alloc_node(struct kmem_cache *cachep, gfp_t flags, int nodeid, > > +slab_alloc_node(struct kmem_cache *cachep, gfp_t flags, int nodeid, size_t orig_size, > > unsigned long caller) > > { > > The size of the object is available via a field in kmem_cache. And a > pointer to the current kmem_cache is already passed to the function. Why > is there a need to add an additional parameter? That's because we want to do our best detecting bugs on kmalloc-allocated objects. kmalloc is using size classes, so e.g. when allocating 272 bytes the object will be padded to 512. As a result, placing that object at the end of the page won't really help to detect out-of-bound accesses that are off by less than 270 bytes. We probably need to better clarify this in the patch description. -- Alexander Potapenko Software Engineer Google Germany GmbH Erika-Mann-Straße, 33 80636 München Geschäftsführer: Paul Manicle, Halimah DeLaine Prado Registergericht und -nummer: Hamburg, HRB 86891 Sitz der Gesellschaft: Hamburg
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