On Tue, Aug 02, 2016 at 12:04:34PM -0700, Kees Cook wrote: > Now, obviously, these API have huge value, otherwise they wouldn't > exist in the first place, and they wouldn't be built into end-user > kernels if they were universally undesirable. But that's not the > situation: the APIs are needed, but they lack the appropriate knobs to > control their availability. So far so good, but I take exception with the suggestion that the proposed knob is appropriate. > And this isn't just about Android: regular > distro kernels (like Debian, who also uses this patch) tend to build > in everything so people can use whatever they want. But for admins > that want to reduce their systems' attack surface, there needs to be > ways to disable things like this. And here I think you're overestimating the knowledge of most admins. > > So the problem I have with this is that it will completely inhibit > > development of things like JITs that self-profile to re-compile > > frequently used code. > > This is a good example of a use-case where this knob would be turned > down. But for many many other use-cases, when presented with a > pre-built kernel, there isn't a way to remove the attack surface. No, quite the opposite. Having this knob will completely inhibit development of such applications. Worse it will probably render perf dead for quite a large body of developers. The moment you frame it like: perf or sekjurity, and even default to no-perf-because-sekjurity, a whole bunch of corporate IT departments will not enable this, even for their developers. Have you never had to 'root' your work machine to get work done? I have. Luckily this was pre-secure-boot times so it was trivial since I had physical access to the machine. But it still sucked I had to fight IT over mostly 'trivial' crap. > > I would much rather have an LSM hook where the security stuff can do > > more fine grained control of things. Allowing some apps perf usage while > > denying others. > > I'm not against an LSM, but I think it's needless complexity when > there is already a knob for this but it just doesn't go "high" enough. > :) So what will you to the moment the Google Dalvik guys come to you and say: "Hey, we want to do active profiling to do better on-line code generation?". I see 0 up-sides of this approach and, as per the above, a whole bunch of very serious downsides. A global (esp. default inhibited) knob is too coarse and limiting. -- To unsubscribe from this list: send the line "unsubscribe linux-doc" in the body of a message to majordomo@xxxxxxxxxxxxxxx More majordomo info at http://vger.kernel.org/majordomo-info.html
