Re: [PATCH 1/2] mm/slub: remove redundant kasan_reset_tag() from freelist_ptr calculations

[Kees Cook]

On Tue, Jul 11, 2023 at 03:46:24PM +0200, Vlastimil Babka wrote:
> Commit d36a63a943e3 ("kasan, slub: fix more conflicts with
> CONFIG_SLAB_FREELIST_HARDENED") has introduced kasan_reset_tags() to
> freelist_ptr() encoding/decoding when CONFIG_SLAB_FREELIST_HARDENED is
> enabled to resolve issues when passing tagged or untagged pointers
> inconsistently would lead to incorrect calculations.
> 
> Later, commit aa1ef4d7b3f6 ("kasan, mm: reset tags when accessing
> metadata") made sure all pointers have tags reset regardless of
> CONFIG_SLAB_FREELIST_HARDENED, because there was no other way to access
> the freepointer metadata safely with hw tag-based KASAN.
> 
> Therefore the kasan_reset_tag() usage in freelist_ptr_encode()/decode()
> is now redundant, as all callers use kasan_reset_tag() unconditionally
> when constructing ptr_addr. Remove the redundant calls and simplify the
> code and remove obsolete comments.
> 
> Also in freelist_ptr_encode() introduce an 'encoded' variable to make
> the lines shorter and make it similar to the _decode() one.
> 
> Signed-off-by: Vlastimil Babka <vbabka@xxxxxxx>

Thanks, this is much more readable!

Acked-by: Kees Cook <keescook@xxxxxxxxxxxx>

-- 
Kees Cook