linux-kernel - Re: [RFC PATCH V2 00/11] Intel EPT-Based Sub-page Protection Support

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Date:   Mon, 03 Dec 2018 05:56:13 +0200
From:   Mihai Donțu <mdontu@...defender.com>
To:     Paolo Bonzini <pbonzini@...hat.com>
Cc:     rkrcmar@...hat.com, linux-kernel@...r.kernel.org,
        kvm@...r.kernel.org, Nicusor CITU <ncitu@...defender.com>,
        Zhang Yi <yi.z.zhang@...ux.intel.com>,
        Adalbert Lazăr <alazar@...defender.com>
Subject: Re: [RFC PATCH V2 00/11] Intel EPT-Based Sub-page Protection Support

Hi Paolo,

On Fri, 2018-11-30 at 11:07 +0100, Paolo Bonzini wrote:
> On 30/11/18 08:52, Zhang Yi wrote:
> > Here is a patch-series which adding EPT-Based Sub-page Write Protection Support.
> > 
> > Introduction:
> > 
> > EPT-Based Sub-page Write Protection referred to as SPP, it is a capability which
> > allow Virtual Machine Monitors(VMM) to specify write-permission for guest
> > physical memory at a sub-page(128 byte) granularity.  When this capability is
> > utilized, the CPU enforces write-access permissions for sub-page regions of 4K
> > pages as specified by the VMM. EPT-based sub-page permissions is intended to
> > enable fine-grained memory write enforcement by a VMM for security(guest OS
> > monitoring) and usages such as device virtualization and memory check-point.
> > 
> > SPPT is active when the "sub-page write protection" VM-execution control is 1.
> > SPPT looks up the guest physical addresses to derive a 64 bit "sub-page
> > permission" value containing sub-page write permissions. The lookup from
> > guest-physical addresses to the sub-page region permissions is determined by a
> > set of SPPT paging structures.
> > 
> > When the "sub-page write protection" VM-execution control is 1, the SPPT is used
> > to lookup write permission bits for the 128 byte sub-page regions containing in
> > the 4KB guest physical page. EPT specifies the 4KB page level privileges that
> > software is allowed when accessing the guest physical address, whereas SPPT
> > defines the write permissions for software at the 128 byte granularity regions
> > within a 4KB page. Write accesses prevented due to sub-page permissions looked
> > up via SPPT are reported as EPT violation VM exits. Similar to EPT, a logical
> > processor uses SPPT to lookup sub-page region write permissions for
> > guest-physical addresses only when those addresses are used to access memory.
> 
> Hi,
> 
> I think the right thing to do here would be to first get VM
> introspection in KVM, as SPP is mostly an introspection feature and it
> should be controller by the introspector rather than the KVM userspace.
> 
> Mihai, if you resubmit, I promise that I will look at it promptly.

I'm currently traveling until Wednesday, but when I'll get into the
office I will see about preparing a new patch set and send it to the
list before Christmas.

Regards,

-- 
Mihai Donțu