On Fri, Apr 19, 2024 at 10:03 AM Mike Rapoport [off-list ref] wrote:
[...]

quoted

quoted

[1] https://lore.kernel.org/all/20240411160526.2093408-1-rppt@kernel.org (local)

For the ROX to work, we need different users (module text, kprobe, etc.) to have
the same execmem_range. From [1]:

static void *execmem_cache_alloc(struct execmem_range *range, size_t size)
{
...
       p = __execmem_cache_alloc(size);
       if (p)
               return p;
      err = execmem_cache_populate(range, size);
...
}

We are calling __execmem_cache_alloc() without range. For this to work,
we can only call execmem_cache_alloc() with one execmem_range.

Actually, on x86 this will "just work" because everything shares the same
address space :)

The 2M pages in the cache will be in the modules space, so
__execmem_cache_alloc() will always return memory from that address space.

For other architectures this indeed needs to be fixed with passing the
range to __execmem_cache_alloc() and limiting search in the cache for that
range.

I think we at least need the "map to" concept (initially proposed by Thomas)
to get this work. For example, EXECMEM_BPF and EXECMEM_KPROBE
maps to EXECMEM_MODULE_TEXT, so that all these actually share
the same range.

Does this make sense?

Song