On Mon, Mar 25, 2024 at 03:32:12PM -0400, Kent Overstreet wrote: > On Mon, Mar 25, 2024 at 10:03:23AM +0100, Vlastimil Babka wrote: > > 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. > > There shouldn't be any need to convert users to this interface - just > leverage the alloc_hooks() macro. I expect to do both -- using the alloc_hooks() macro to do per-call-site-allocation caches will certainly have a non-trivial amount of memory usage overhead, and not all systems will want it. We can have a boot param to choose between per-site and normal, though normal can include a handful of these manually identified places. -- Kees Cook
