From: Sean Christopherson <sean.j.christopherson@intel.com>
To: Alexander Graf <agraf@csgraf.de>
Cc: "Mihai Donțu" <mdontu@bitdefender.com>,
"Paolo Bonzini" <pbonzini@redhat.com>,
kvm@vger.kernel.org, "KarimAllah Ahmed" <karahmed@amazon.de>
Subject: Re: #VE support for VMI
Date: Mon, 20 May 2019 11:33:31 -0700 [thread overview]
Message-ID: <20190520183331.GD28482@linux.intel.com> (raw)
In-Reply-To: <80e0baaf-150b-0966-6920-b36d23a6cdef@csgraf.de>
On Mon, May 20, 2019 at 11:10:51AM -0700, Alexander Graf wrote:
> On 20.05.19 08:48, Mihai Donțu wrote:
> > Hi Paolo,
> >
> > We are looking at adding #VE support to the VMI subsystem we are
> > working on. Its purpose is to suppress VMEXIT-s caused by the page
> > table walker when the guest page tables are write-protected. A very
> > small in-guest agent (protected by the hypervisor) will receive the EPT
> > violation events, handle PT-walk writes and turn the rest into VMCALL-
> > s.
> >
> > A brief presentation of similar work on Xen can be found here:
> > https://www.slideshare.net/xen_com_mgr/xpdss17-hypervisorbased-security-bringing-virtualized-exceptions-into-the-game-mihai-dontu-bitdefender
> >
> > There is a bit of an issue with using #VE on KVM, though: because the
> > EPT is built on-the-fly (as the guest runs), when we enable #VE in
> > VMCS, all EPT violations become virtualized, because all EPTE-s have
> > bit 63 zero (0: convert to #VE, 1: generate VMEXIT). At the moment, I
>
> Are you 100% sure? Last time I played with #VE, it only triggered on
> misconfigurations/permission checks (lack of R/W/X, but P=1), not on P=0
> pages.
#VEs trigger on RWX=0, but not misconfigurations, i.e. any and all
EPT_VIOLATION exits (reason 48) are convertible, and EPT_MISCONFIG exits
(reason 49) are never convertible. The reasoning behind the logic is
that an EPT_MISCONFIG is the result of a VMM bug (or in KVM's case, MMIO
trickery), whereas a RWX=0 EPT_VIOLATION could be a malicious entity in
the guest probing non-existent pages or pages it doesn't have access to.
next prev parent reply other threads:[~2019-05-20 18:33 UTC|newest]
Thread overview: 6+ messages / expand[flat|nested] mbox.gz Atom feed top
2019-05-20 15:48 #VE support for VMI Mihai Donțu
2019-05-20 18:10 ` Alexander Graf
2019-05-20 18:33 ` Sean Christopherson [this message]
2019-05-20 20:49 ` Alexander Graf
2019-05-20 18:22 ` Sean Christopherson
2019-05-20 19:55 ` Mihai Donțu
Reply instructions:
You may reply publicly to this message via plain-text email
using any one of the following methods:
* Save the following mbox file, import it into your mail client,
and reply-to-all from there: mbox
Avoid top-posting and favor interleaved quoting:
https://en.wikipedia.org/wiki/Posting_style#Interleaved_style
* Reply using the --to, --cc, and --in-reply-to
switches of git-send-email(1):
git send-email \
--in-reply-to=20190520183331.GD28482@linux.intel.com \
--to=sean.j.christopherson@intel.com \
--cc=agraf@csgraf.de \
--cc=karahmed@amazon.de \
--cc=kvm@vger.kernel.org \
--cc=mdontu@bitdefender.com \
--cc=pbonzini@redhat.com \
/path/to/YOUR_REPLY
https://kernel.org/pub/software/scm/git/docs/git-send-email.html
* If your mail client supports setting the In-Reply-To header
via mailto: links, try the mailto: link
Be sure your reply has a Subject: header at the top and a blank line
before the message body.
This is an external index of several public inboxes,
see mirroring instructions on how to clone and mirror
all data and code used by this external index.