Re: [PATCH RFC 0/2] Break heap spraying needed for exploiting use-after-free

[Kees Cook]

On Thu, Aug 13, 2020 at 06:19:20PM +0300, Alexander Popov wrote:
> I've found an easy way to break heap spraying for use-after-free
> exploitation. I simply extracted slab freelist quarantine from KASAN
> functionality and called it CONFIG_SLAB_QUARANTINE. Please see patch 1.

Ah yeah, good idea. :)

> [...]
> I did a brief performance evaluation of this feature.
> 
> 1. Memory consumption. KASAN quarantine uses 1/32 of the memory.
> CONFIG_SLAB_QUARANTINE disabled:
>   # free -m
>                 total        used        free      shared  buff/cache   available
>   Mem:           1987          39        1862          10          86        1907
>   Swap:             0           0           0
> CONFIG_SLAB_QUARANTINE enabled:
>   # free -m
>                 total        used        free      shared  buff/cache   available
>   Mem:           1987         140        1760          10          87        1805
>   Swap:             0           0           0

1/32 of memory doesn't seem too bad for someone interested in this defense.

> 2. Performance penalty. I used `hackbench -s 256 -l 200 -g 15 -f 25 -P`.
> CONFIG_SLAB_QUARANTINE disabled (x86_64, CONFIG_SLUB):
>   Times: 3.088, 3.103, 3.068, 3.103, 3.107
>   Mean: 3.0938
>   Standard deviation: 0.0144
> CONFIG_SLAB_QUARANTINE enabled (x86_64, CONFIG_SLUB):
>   Times: 3.303, 3.329, 3.356, 3.314, 3.292
>   Mean: 3.3188 (+7.3%)
>   Standard deviation: 0.0223

That's rather painful, but hackbench can produce some big deltas given
it can be an unrealistic workload for most systems. I'd be curious to
see the "building a kernel" timings, which tends to be much more
realistic for "busy system" without hammering one particular subsystem
(though it's a bit VFS heavy, obviously).

More notes in the patches...

-- 
Kees Cook