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Date:   Thu, 23 Nov 2017 11:47:52 +0100
From:   Pavel Machek <>
To:     Dave Hansen <>
Subject: Re: [PATCH 00/23] KAISER: unmap most of the kernel from userspace
 page tables

On Wed 2017-11-22 17:19:07, Pavel Machek wrote:
> 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?

Issues with AnC attacks are tracked via several CVE identifiers.

CVE-2017-5925 is assigned to track the developments for Intel processors
CVE-2017-5926 is assigned to track the developments for AMD processors


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