Bug 209821

Summary:	KASAN: improve x2 memory overhead for kmalloc objects
Product:	Memory Management	Reporter:	Andrey Konovalov (andreyknvl)
Component:	Sanitizers	Assignee:	MM/Sanitizers virtual assignee (mm_sanitizers)
Status:	RESOLVED CODE_FIX
Severity:	normal	CC:	kasan-dev
Priority:	P1
Hardware:	All
OS:	Linux
Kernel Version:	upstream	Subsystem:
Regression:	No	Bisected commit-id:

Description Andrey Konovalov 2020-10-22 21:29:43 UTC

As of [1] kmalloc return value is aligned to the size of the allocation for power-of-two kmalloc caches. As KASAN adds just a few bytes of metadata after each object, this results in x2 memory usage increase for such kmalloc caches.

[1] https://git.kernel.org/pub/scm/linux/kernel/git/torvalds/linux.git/commit/?id=59bb47985c1db229ccff8c5deebecd54fc77d2a9

Comment 1 Andrey Konovalov 2022-10-18 18:57:26 UTC

This has been resolved for the Software and Hardware Tag-Based modes by moving stack trace handles from per-object metadata to the stack ring [1].

For Generic KASAN, the additional memory usage caused by the over-alignment of kmalloc objects is not that critical, as it introduces a significant memory overhead anyway.

Thus, this issue is considered resolved.

[1] https://git.kernel.org/pub/scm/linux/kernel/git/torvalds/linux.git/commit/?id=ca77f290cff1dfa095d71ae16cc7cda8ee6df495