linux-kernel - Re: [PATCH v2 04/10] mm, kfence: insert KFENCE hooks for SLAB

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Message-ID: <CAG_fn=XMc8NPZPFtUE=rdoR=XJH4F+TxZs-w5n4VuaWKTjcasw@mail.gmail.com>
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

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