Received-SPF: pass (google.com: domain of linux-kernel-owner@vger.kernel.org designates 23.128.96.18 as permitted sender) client-ip=23.128.96.18;
MIME-Version: 1.0
References: <20201029131649.182037-1-elver@google.com> <20201029131649.182037-5-elver@google.com>
In-Reply-To: <20201029131649.182037-5-elver@google.com>
From:   Jann Horn <jannh@google.com>
Date:   Fri, 30 Oct 2020 03:49:31 +0100
Message-ID: <CAG48ez1DxttDs6vj61c0jSGSbhoUmAW9_OSBSENrC-=hz-d+HA@mail.gmail.com>
Subject: Re: [PATCH v6 4/9] mm, kfence: insert KFENCE hooks for SLAB
To:     Marco Elver <elver@google.com>
Cc:     Andrew Morton <akpm@linux-foundation.org>,
        Alexander Potapenko <glider@google.com>,
        "H . Peter Anvin" <hpa@zytor.com>,
        "Paul E . McKenney" <paulmck@kernel.org>,
        Andrey Konovalov <andreyknvl@google.com>,
        Andrey Ryabinin <aryabinin@virtuozzo.com>,
        Andy Lutomirski <luto@kernel.org>,
        Borislav Petkov <bp@alien8.de>,
        Catalin Marinas <catalin.marinas@arm.com>,
        Christoph Lameter <cl@linux.com>,
        Dave Hansen <dave.hansen@linux.intel.com>,
        David Rientjes <rientjes@google.com>,
        Dmitry Vyukov <dvyukov@google.com>,
        Eric Dumazet <edumazet@google.com>,
        Greg Kroah-Hartman <gregkh@linuxfoundation.org>,
        Hillf Danton <hdanton@sina.com>,
        Ingo Molnar <mingo@redhat.com>,
        Jonathan Cameron <Jonathan.Cameron@huawei.com>,
        Jonathan Corbet <corbet@lwn.net>,
        Joonsoo Kim <iamjoonsoo.kim@lge.com>, joern@purestorage.com,
        Kees Cook <keescook@chromium.org>,
        Mark Rutland <mark.rutland@arm.com>,
        Pekka Enberg <penberg@kernel.org>,
        Peter Zijlstra <peterz@infradead.org>,
        SeongJae Park <sjpark@amazon.com>,
        Thomas Gleixner <tglx@linutronix.de>,
        Vlastimil Babka <vbabka@suse.cz>,
        Will Deacon <will@kernel.org>,
        "the arch/x86 maintainers" <x86@kernel.org>,
        "open list:DOCUMENTATION" <linux-doc@vger.kernel.org>,
        kernel list <linux-kernel@vger.kernel.org>,
        kasan-dev <kasan-dev@googlegroups.com>,
        Linux ARM <linux-arm-kernel@lists.infradead.org>,
        Linux-MM <linux-mm@kvack.org>
Content-Type: text/plain; charset="UTF-8"
Precedence: bulk

On Thu, Oct 29, 2020 at 2:17 PM Marco Elver <elver@google.com> wrote:
> Inserts KFENCE hooks into the SLAB allocator.
[...]
> diff --git a/mm/slab.c b/mm/slab.c
[...]
> @@ -3416,6 +3427,11 @@ static void cache_flusharray(struct kmem_cache *cachep, struct array_cache *ac)
>  static __always_inline void __cache_free(struct kmem_cache *cachep, void *objp,
>                                          unsigned long caller)
>  {
> +       if (kfence_free(objp)) {
> +               kmemleak_free_recursive(objp, cachep->flags);
> +               return;
> +       }

This looks dodgy. Normally kmemleak is told that an object is being
freed *before* the object is actually released. I think that if this
races really badly, we'll make kmemleak stumble over this bit in
create_object():

kmemleak_stop("Cannot insert 0x%lx into the object search tree
(overlaps existing)\n",
      ptr);


> +
>         /* Put the object into the quarantine, don't touch it for now. */
>         if (kasan_slab_free(cachep, objp, _RET_IP_))
>                 return;