Bug 218321

Summary:	KASAN (tags): skip poisoning new slabs
Product:	Memory Management	Reporter:	Andrey Konovalov (andreyknvl)
Component:	Sanitizers	Assignee:	MM/Sanitizers virtual assignee (mm_sanitizers)
Status:	NEW ---
Severity:	normal	CC:	kasan-dev
Priority:	P3
Hardware:	All
OS:	Linux
Kernel Version:		Subsystem:
Regression:	No	Bisected commit-id:

Description Andrey Konovalov 2023-12-25 23:51:01 UTC

Currently, all KASAN modes poison newly allocated slabs via kasan_poison_slab. While doing this makes sense for the Generic mode to poison the redzones within the slab, the tag-based modes have no redzones.

We should skip poisoning of new slabs for the tag-based modes. The objects get unpoisoned/poisoned on alloc/free anyway.

For this, we need to:

1. Stop poisoning slab memory via kasan_poison in kasan_poison_slab;

2. Skip unpoisoning of the page allocation for the slab via the __GFP_SKIP_KASAN flag. The flag is only functional for the Hardware Tag-Based mode right now, but we can extend it to the Software one too.

Once both are implemented, we can drop page_kasan_tag_reset from kasan_poison_slab, and we can thus make kasan_poison_slab no-op for the tag-based modes.