It certainly isn't something you can just turn on. I don't know how hardened_malloc works, but one problem is that C malloc() doesn't know the type of memory it's allocating, which is naturally an issue when you need to… allocate typed memory.

You can fix this insofar as you control the compiler and calls to malloc(), which you don't, because third party code may have wrappers around it.

MTE is not about typed memory. It's for detecting invalid memory accesses outside of an object or outside of the lifetime of the object in general. hardened_malloc is the main place GrapheneOS implements MTE for userspace. In the kernel, it's implemented in various allocators and in Chromium in PartitionAlloc. The kernel and PartitionAlloc allocators have typed allocator designed unlike malloc. It's still possible to do partitioning for malloc via size classes and call locations.