Re: [PATCH v3 1/1] kasan: Add memzero init for unaligned size under SLUB debug

On Wed, Jun 30, 2021 at 10:13 PM Marco Elver [off-list ref] wrote:

quoted

+     if (IS_ENABLED(CONFIG_SLUB_DEBUG) && init && ((unsigned long)size & KASAN_GRANULE_MASK)) {
+             init = false;
+             memzero_explicit((void *)addr, size);
+     }
      size = round_up(size, KASAN_GRANULE_SIZE);

      hw_set_mem_tag_range((void *)addr, size, tag, init);

I think this solution might be fine for now, as I don't see an easy way
to do this without some major refactor to use kmem_cache_debug_flags().

However, I think there's an intermediate solution where we only check
the static-key 'slub_debug_enabled' though. Because I've checked, and
various major distros _do_ enabled CONFIG_SLUB_DEBUG. But the static
branch just makes sure there's no performance overhead.

Checking the static branch requires including mm/slab.h into
mm/kasan/kasan.h, which we currently don't do and perhaps wanted to
avoid. Although I don't see a reason there, because there's no circular
dependency even if we did.

Most likely this won't be a problem. We already include ../slab.h into
many mm/kasan/*.c files.

Andrey, any opinion?

I like this approach. Easy to implement and is better than checking
only CONFIG_SLUB_DEBUG.

Thanks, Marco!

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