On Mon, Aug 25, 2025 at 10:29 PM Maciej Wieczor-Retman <maciej.wieczor-retman@xxxxxxxxx> wrote: > > 8 byte minimal SLAB alignment interferes with KASAN's granularity of 16 > bytes. It causes a lot of out-of-bounds errors for unaligned 8 byte > allocations. > > Compared to a kernel with KASAN disabled, the memory footprint increases > because all kmalloc-8 allocations now are realized as kmalloc-16, which > has twice the object size. But more meaningfully, when compared to a > kernel with generic KASAN enabled, there is no difference. Because of > redzones in generic KASAN, kmalloc-8' and kmalloc-16' object size is the > same (48 bytes). So changing the minimal SLAB alignment of the tag-based > mode doesn't have any negative impact when compared to the other > software KASAN mode. > > Adjust x86 minimal SLAB alignment to match KASAN granularity size. > > Signed-off-by: Maciej Wieczor-Retman <maciej.wieczor-retman@xxxxxxxxx> > --- > Changelog v4: > - Extend the patch message with some more context and impact > information. > > Changelog v3: > - Fix typo in patch message 4 -> 16. > - Change define location to arch/x86/include/asm/cache.c. > > arch/x86/include/asm/cache.h | 4 ++++ > 1 file changed, 4 insertions(+) > > diff --git a/arch/x86/include/asm/cache.h b/arch/x86/include/asm/cache.h > index 69404eae9983..3232583b5487 100644 > --- a/arch/x86/include/asm/cache.h > +++ b/arch/x86/include/asm/cache.h > @@ -21,4 +21,8 @@ > #endif > #endif > > +#ifdef CONFIG_KASAN_SW_TAGS > +#define ARCH_SLAB_MINALIGN (1ULL << KASAN_SHADOW_SCALE_SHIFT) > +#endif > + > #endif /* _ASM_X86_CACHE_H */ > -- > 2.50.1 > Reviewed-by: Andrey Konovalov <andreyknvl@xxxxxxxxx>
