We’ve just released a rather interesting batch of Xen security advisories. This has given rise in some quarters to grumbling around Xen not taking security seriously.
I have a longstanding interest in computer security. Nowadays I am a member of the Xen Project Security Team (the team behind security@xenproject, which drafts the advisories and coordinates the response). But I’m going to put forward my personal opinions.
Of course Invisible Things are completely right that security isn’t taken seriously enough. The general state of computer security in almost all systems is very poor. The reason for this is quite simple: we all put up with it. We, collectively, choose convenience and functionality: both when we decide which software to run for ourselves, and when we decide what contributions to make to the projects we care about. For almost all software there is much stronger pressure (from all sides) to add features, than to improve security.
That’s not to say that many of us working on Xen aren’t working to improve matters. The first part of improving anything is to know what the real situation is. Unlike almost all corporations, and even most Free Software projects, the Xen Project properly discloses, via an advisory, every vulnerability discovered in supported configurations. We also often publish advisories about vulnerabilities in other relevant projects, such as Linux and QEMU.
Security bugs are bugs, and over the last few years the Xen Project’s code review process has become a lot more rigorous. As a result, the quality of code being newly introduced into Xen has improved a lot.
For researchers developing new analysis techniques, Xen is a prime target. A significant proportion of the reports to security@xenproject are the result of applying new scanning techniques to our codebase. So our existing code is being audited, with a focus on the areas and techniques likely to discover the most troublesome bugs.
As I say, the Xen Project is very transparent about disclosing security issues; much more so than other projects. This difference in approach to disclosure makes it difficult to compare the security bug density of competing systems. When I worked for a security hardware vendor I was constantly under pressure to explain why we needed to do a formal advisory for our bugs. That is what security-conscious users expect, but our competitors’ salesfolk would point to our advisories and say that our products were full of bugs. Their products had no publicly disclosed security bugs, so they would tell naive customers that their products had no bugs.
I do think Xen probably has fewer critical security bugs than other hypervisors (whether Free or proprietary). It’s the best available platform for building high security systems. The Xen Project’s transparency is very good for Xen’s users. But that doesn’t mean Xen is good enough.
Ultimately, of course, a Free Software project like Xen is what the whole community makes it. In the project as a whole we get a lot more submissions of new functionality than we get submissions aimed at improving the security.
So personally, I very much welcome the contributions made by security-focused contributors – even if that includes criticism.