linux-kernel - Re: [PATCH 00/23] KAISER: unmap most of the kernel from userspace page tables

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Message-ID: <20171122161907.GA12684@amd>
Date:   Wed, 22 Nov 2017 17:19:07 +0100
From:   Pavel Machek <pavel@....cz>
To:     Dave Hansen <dave.hansen@...ux.intel.com>
Cc:     linux-kernel@...r.kernel.org, linux-mm@...ck.org
Subject: Re: [PATCH 00/23] KAISER: unmap most of the kernel from userspace
 page tables

Hi!

> KAISER makes it harder to defeat KASLR, but makes syscalls and
> interrupts slower.  These patches are based on work from a team at
> Graz University of Technology posted here[1].  The major addition is
> support for Intel PCIDs which builds on top of Andy Lutomorski's PCID
> work merged for 4.14.  PCIDs make KAISER's overhead very reasonable
> for a wide variety of use cases.

Is it useful?

> Full Description:
> 
> KAISER is a countermeasure against attacks on kernel address
> information.  There are at least three existing, published,
> approaches using the shared user/kernel mapping and hardware features
> to defeat KASLR.  One approach referenced in the paper locates the
> kernel by observing differences in page fault timing between
> present-but-inaccessable kernel pages and non-present pages.

I mean... evil userspace will still be able to determine kernel's
location using cache aliasing effects, right?
									Pavel
-- 
(english) http://www.livejournal.com/~pavelmachek
(cesky, pictures) http://atrey.karlin.mff.cuni.cz/~pavel/picture/horses/blog.html

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