Date: Fri, 25 Aug 2023 23:22:03 +0200 From: Jann Horn <jannh@...gle.com> To: Kernel Hardening <kernel-hardening@...ts.openwall.com> Cc: Christoph Lameter <cl@...ux.com>, Pekka Enberg <penberg@...nel.org>, David Rientjes <rientjes@...gle.com>, Joonsoo Kim <iamjoonsoo.kim@....com>, Andrew Morton <akpm@...ux-foundation.org>, Linux-MM <linux-mm@...ck.org>, Andrey Konovalov <andreyknvl@...gle.com>, Dmitry Vyukov <dvyukov@...gle.com>, Will Deacon <will@...nel.org>, kasan-dev <kasan-dev@...glegroups.com>, Kees Cook <keescook@...gle.com>, Alexander Potapenko <glider@...gle.com>, Marco Elver <elver@...gle.com> Subject: Re: Kernel hardening project suggestion: Normalizing ->ctor slabs and TYPESAFE_BY_RCU slabs On Tue, Jun 23, 2020 at 8:26 AM Jann Horn <jannh@...gle.com> wrote: > Here's a project idea for the kernel-hardening folks: > > The slab allocator interface has two features that are problematic for > security testing and/or hardening: > > - constructor slabs: These things come with an object constructor > that doesn't run when an object is allocated, but instead when the > slab allocator grabs a new page from the page allocator. This is > problematic for use-after-free detection mechanisms such as HWASAN and > Memory Tagging, which can only do their job properly if the address of > an object is allowed to change every time the object is > freed/reallocated. (You can't change the address of an object without > reinitializing the entire object because e.g. an empty list_head > points to itself.) > > - RCU slabs: These things basically permit use-after-frees by design, > and stuff like ASAN/HWASAN/Memory Tagging essentially doesn't work on > them. > > > It would be nice to have a config flag or so that changes the SLUB > allocator's behavior such that these slabs can be instrumented > properly. Something like: > > - Let calculate_sizes() reserve space for an rcu_head on each object > in TYPESAFE_BY_RCU slabs, make kmem_cache_free() redirect to > call_rcu() for these slabs, and remove most of the other > special-casing, so that KASAN can instrument these slabs. I've implemented this first part now and sent it out for review: https://email@example.com/T/ > - For all constructor slabs, let slab_post_alloc_hook() call the > ->ctor() function on each allocated object, so that Memory Tagging and > HWASAN will work on them.
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