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 +e94K5kd 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 X-Bogosity: Ham, tests=bogofilter, spamicity=0.000000, version=1.2.4 Sender: owner-linux-mm@kvack.org Precedence: bulk X-Loop: owner-majordomo@kvack.org List-ID: List-Subscribe: List-Unsubscribe: On Wed, Oct 29, 2025 at 03:36:28PM +0100, Andrey Ryabinin wrote: > > > On 10/27/25 1:00 PM, Harry Yoo wrote: > > When the SLAB_STORE_USER debug flag is used, any metadata placed after > > the original kmalloc request size (orig_size) is not properly aligned > > on 64-bit architectures because its type is unsigned int. When both KASAN > > and SLAB_STORE_USER are enabled, kasan_alloc_meta is misaligned. > > > > kasan_alloc_meta is properly aligned. It consists of 4 32-bit words, > so the proper alignment is 32bit regardless of architecture bitness. Right. > kasan_free_meta however requires 'unsigned long' alignment > and could be misaligned if placed at 32-bit boundary on 64-bit arch Right. > > Note that 64-bit architectures without HAVE_EFFICIENT_UNALIGNED_ACCESS > > are assumed to require 64-bit accesses to be 64-bit aligned. > > See HAVE_64BIT_ALIGNED_ACCESS and commit adab66b71abf ("Revert: > > "ring-buffer: Remove HAVE_64BIT_ALIGNED_ACCESS"") for more details. > > > > Because not all architectures support unaligned memory accesses, > > ensure that all metadata (track, orig_size, kasan_{alloc,free}_meta) > > in a slab object are word-aligned. struct track, kasan_{alloc,free}_meta > > are aligned by adding __aligned(__alignof__(unsigned long)). > > > > __aligned() attribute ensures nothing. It tells compiler what alignment to expect > and affects compiler controlled placement of struct in memory (e.g. stack/.bss/.data) > But it can't enforce placement in dynamic memory. Right. > Also for struct kasan_free_meta, struct track alignof(unsigned long) already dictated > by C standard, so adding this __aligned() have zero effect. Right. > And there is no reason to increase alignment requirement for kasan_alloc_meta struct. Right. > > For orig_size, use ALIGN(sizeof(unsigned int), sizeof(unsigned long)) to > > make clear that its size remains unsigned int but it must be aligned to > > a word boundary. On 64-bit architectures, this reserves 8 bytes for > > orig_size, which is acceptable since kmalloc's original request size > > tracking is intended for debugging rather than production use. > > I would suggest to use 'unsigned long' for orig_size. It changes nothing for 32-bit, > and it shouldn't increase memory usage for 64-bit since we currently wasting it anyway > to align next object to ARCH_KMALLOC_MINALIGN. Sounds fair! Patch soon. Thanks. -- Cheers, Harry / Hyeonggon