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

[Vlastimil Babka]

On 3/5/24 11:10 AM, 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().)
> 
>     Allows for confining allocations to a dedicated set of sized caches
>     (which have the same layout as the kmalloc caches).
> 
>     This can also be used in the future once codetag allocation annotations
>     exist to implement per-caller allocation cache isolation[0] even for
>     dynamic allocations.
> 
>     Link: https://lore.kernel.org/lkml/202402211449.401382D2AF@keescook [0]
> 
> After the implemetation are 2 example patches of how this could be used
> for some repeat "offenders" that get used in exploits. There are more to
> be isolated beyond just these. Repeating the commit log for patch 8 here:
> 
>     The msg subsystem is a common target for exploiting[1][2][3][4][5][6]
>     use-after-free type confusion flaws in the kernel for both read and
>     write primitives. Avoid having a user-controlled size cache share the
>     global kmalloc allocator by using a separate set of kmalloc buckets.
> 
>     Link: https://blog.hacktivesecurity.com/index.php/2022/06/13/linux-kernel-exploit-development-1day-case-study/ [1]
>     Link: https://hardenedvault.net/blog/2022-11-13-msg_msg-recon-mitigation-ved/ [2]
>     Link: https://www.willsroot.io/2021/08/corctf-2021-fire-of-salvation-writeup.html [3]
>     Link: https://a13xp0p0v.github.io/2021/02/09/CVE-2021-26708.html [4]
>     Link: https://google.github.io/security-research/pocs/linux/cve-2021-22555/writeup.html [5]
>     Link: https://zplin.me/papers/ELOISE.pdf [6]

Hi Kees,

after reading [1] I think the points should be addressed, mainly about the
feasibility of converting users manually. On a related technical note I
worry what will become of /proc/slabinfo when we convert non-trivial amounts
of users.

Also would interested to hear Jann Horn et al.'s opinion, and whether the
SLAB_VIRTUAL effort will continue?

Thanks,
Vlastimil


[1]
https://dustri.org/b/notes-on-the-slab-introduce-dedicated-bucket-allocator-series.html

> -Kees
> 
>  v2: significant rewrite, generalized the buckets type, added kvmalloc style
>  v1: https://lore.kernel.org/lkml/20240304184252.work.496-kees@xxxxxxxxxx/
> 
> Kees Cook (9):
>   slab: Introduce kmem_buckets typedef
>   slub: Plumb kmem_buckets into __do_kmalloc_node()
>   util: Introduce __kvmalloc_node() that can take kmem_buckets argument
>   slab: Introduce kmem_buckets_create()
>   slab: Introduce kmem_buckets_alloc()
>   slub: Introduce kmem_buckets_alloc_track_caller()
>   slab: Introduce kmem_buckets_valloc()
>   ipc, msg: Use dedicated slab buckets for alloc_msg()
>   mm/util: Use dedicated slab buckets for memdup_user()
> 
>  include/linux/slab.h | 50 +++++++++++++++++++++-------
>  ipc/msgutil.c        | 13 +++++++-
>  lib/fortify_kunit.c  |  2 +-
>  mm/slab.h            |  6 ++--
>  mm/slab_common.c     | 77 ++++++++++++++++++++++++++++++++++++++++++--
>  mm/slub.c            | 14 ++++----
>  mm/util.c            | 23 +++++++++----
>  7 files changed, 154 insertions(+), 31 deletions(-)
>