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A Discussion of Software Security

September 4, 2018

Containers or virtual machines--which provides greater security? IBM Research attempted to answer this question, as explained in this recent article:

Are virtual machines (VM) more secure than containers? You may think you know the answer, but IBM Research has found containers can be as secure, or more secure, than VMs.

James Bottomley, an IBM Research Distinguished Engineer and top Linux kernel developer, writes:

"One of the biggest problems with the current debate about Container vs Hypervisor security is that no one has actually developed a way of measuring security, so the debate is all in qualitative terms (hypervisors 'feel' more secure than containers because of the interface breadth) but no one actually has done a quantitative comparison."

To meet this need, Bottomley created Horizontal Attack Profile (HAP), designed to describe system security in a way that it can be objectively measured. Bottomley has discovered that "a Docker container with a well crafted seccomp profile (which blocks unexpected system calls) provides roughly equivalent security to a hypervisor."

He performed these tests with Docker, Google's gVisor, a container runtime sandbox; gVisor-kvm, the same container sandbox using the KVM, Linux's built-in VM hypervisor; Kata Containers, an open-source lightweight VM; and Nabla, IBM's just released container type, which is designed for strong server isolation.

Bottomley's work is only the start. He's shown it's possible to objectively measure an application's security. As he said, "I don't expect this will be the final word in the debate, but by describing how we did it I hope others can develop quantitative measurements as well.

I would need more details, but the article makes it sound like this work was done on x86 with x86 hypervisors. I wonder if the results would be different if the containers ran in Linux on Power with the PowerVM hypervisor:

The PowerVM and Power hardware teams always put security at the center of our designs. Protection of client data is one of the key values of a PowerVM solution. If you ever wondered if your hardware or software are exposed to a security issue, the USA National Institute of Standards and Technology (NIST) maintains a searchable DB of all known vulnerability. Searching for PowerVM or PowerVM Hypervisor will display "There are 0 matching records." This is because the PowerVM Hypervisor have yet to have a security vulnerability. Searching for other virtualization solutions will list all their known vulnerabilities which you should be sure to address to protect your confidential information. The following blog contains details about how PowerVM provides data isolation between partitions to maintain our perfect security record.

PowerVM takes advantage of the Power hardware to provide high levels of security. The hardware is designed with three different protections domains, Hypervisor domain, Kernel domain and application domain. The hardware limits the instructions that can be executed based on the current protection domain and the hardware provides very specific entry points to transition between domains. If a lower priority domain attempts to issue an instruction reserved for a higher priority domain, the instruction will generate an instruction interrupt within the current domain. The most privileged level is the hypervisor domain which is where the PowerVM security takes place. For example, instructions that change the mapping of partition addresses to physical real addresses, instructions that modify specific hardware registers are restricted such that they are only allowed in hypervisor mode.

The way the hardware has been designed, only the hypervisor is able to access memory via a physical real address. Code running in partitions accesses memory through a layer of indirection where the partitions addresses are actually aliases to the physical real memory. This support is not only leveraged for partition isolation but is leveraged by other virtualization functions on the server.

If we're talking about IBM Power Systems servers, I would still argue that an LPAR is more secure. What do you think?

Posted September 4, 2018| Permalink