linux-hardening - Re: [PATCH] mm: reduce lock contention of pcp buffer refill

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Date:   Tue, 14 Feb 2023 09:27:52 -0800
From:   Kees Cook <keescook@...omium.org>
To:     Vlastimil Babka <vbabka@...e.cz>
Cc:     Andrew Morton <akpm@...ux-foundation.org>,
        Alexander Halbuer <halbuer@....uni-hannover.de>,
        "linux-hardening@...r.kernel.org" <linux-hardening@...r.kernel.org>,
        linux-mm@...ck.org, linux-kernel@...r.kernel.org,
        Mel Gorman <mgorman@...hsingularity.net>
Subject: Re: [PATCH] mm: reduce lock contention of pcp buffer refill

On Wed, Feb 08, 2023 at 11:45:14AM +0100, Vlastimil Babka wrote:
> But I wonder also what kernel hardening folks think here - are the hardened
> kernels usually built with DEBUG_VM or debug_pagealloc enabled, or would you
> like to hook some other kernel option for keeping the checks on page/alloc
> free active? And should those checks be done on every alloc/free, including
> pcplist cached allocations?

What we're depending on for heap-related (i.e. both page allocator and
slab) hardening currently is:

- CONFIG_SLAB_FREELIST_HARDENED
	- pointer obfuscation (SLUB) -- freelist_ptr(), set_freepointer()
	- pool membership verification (SLUB and SLAB) -- cache_from_obj()
	- consecutive double free detection (SLUB and SLAB) -- __free_one()
- allocation order randomization
	- CONFIG_SLAB_FREELIST_RANDOM (SLUB and SLAB)
	- CONFIG_SHUFFLE_PAGE_ALLOCATOR (page allocator)
- memory wiping (both slab and page allocator)
	- init_on_alloc / CONFIG_INIT_ON_ALLOC_DEFAULT_ON
	- init_on_free / CONFIG_INIT_ON_FREE_DEFAULT_ON

I'd be nice to gain slab redzone verification, but that seems expensive
enough that anyone interested in that level of hardening has likely
turned on full KASAN.

-- 
Kees Cook