linux-hardening - Re: [PATCH v2 0/9] slab: Introduce dedicated bucket allocator

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Date: Wed, 6 Mar 2024 09:47:36 +0800
From: "GONG, Ruiqi" <gongruiqi@...weicloud.com>
To: Kees Cook <keescook@...omium.org>, Vlastimil Babka <vbabka@...e.cz>
Cc: Andrew Morton <akpm@...ux-foundation.org>,
 Christoph Lameter <cl@...ux.com>, Pekka Enberg <penberg@...nel.org>,
 David Rientjes <rientjes@...gle.com>, Joonsoo Kim <iamjoonsoo.kim@....com>,
 Roman Gushchin <roman.gushchin@...ux.dev>,
 Hyeonggon Yoo <42.hyeyoo@...il.com>, Xiu Jianfeng <xiujianfeng@...wei.com>,
 Suren Baghdasaryan <surenb@...gle.com>,
 Kent Overstreet <kent.overstreet@...ux.dev>, Jann Horn <jannh@...gle.com>,
 Matteo Rizzo <matteorizzo@...gle.com>, linux-kernel@...r.kernel.org,
 linux-mm@...ck.org, linux-hardening@...r.kernel.org
Subject: Re: [PATCH v2 0/9] slab: Introduce dedicated bucket allocator



On 2024/03/05 18:10, Kees Cook wrote:
> Hi,
> 
> Repeating the commit logs for patch 4 here:
> 
>     Dedicated caches are available For fixed size allocations via
>     kmem_cache_alloc(), but for dynamically sized allocations there is only
>     the global kmalloc API's set of buckets available. This means it isn't
>     possible to separate specific sets of dynamically sized allocations into
>     a separate collection of caches.
> 
>     This leads to a use-after-free exploitation weakness in the Linux
>     kernel since many heap memory spraying/grooming attacks depend on using
>     userspace-controllable dynamically sized allocations to collide with
>     fixed size allocations that end up in same cache.
> 
>     While CONFIG_RANDOM_KMALLOC_CACHES provides a probabilistic defense
>     against these kinds of "type confusion" attacks, including for fixed
>     same-size heap objects, we can create a complementary deterministic
>     defense for dynamically sized allocations.
> 
>     In order to isolate user-controllable sized allocations from system
>     allocations, introduce kmem_buckets_create(), which behaves like
>     kmem_cache_create(). (The next patch will introduce kmem_buckets_alloc(),
>     which behaves like kmem_cache_alloc().)

So can I say the vision here would be to make all the kernel interfaces
that handles user space input to use separated caches? Which looks like
creating a "grey zone" in the middle of kernel space (trusted) and user
space (untrusted) memory. I've also thought that maybe hardening on the
"border" could be more efficient and targeted than a mitigation that
affects globally, e.g. CONFIG_RANDOM_KMALLOC_CACHES.