On Thu, Nov 18, 2021 at 10:30:32AM -0800, Casey Schaufler wrote: > On 11/18/2021 9:32 AM, Kees Cook wrote: > > On Tue, Nov 16, 2021 at 11:00:23AM -0800, Casey Schaufler wrote: > > > On 11/16/2021 10:41 AM, Kees Cook wrote: > > > > On Tue, Nov 16, 2021 at 12:12:16PM +0300, Alexander Popov wrote: > > > > > What if the Linux kernel had a LSM module responsible for error handling policy? > > > > > That would require adding LSM hooks to BUG*(), WARN*(), KERN_EMERG, etc. > > > > > In such LSM policy we can decide immediately how to react on the kernel error. > > > > > We can even decide depending on the subsystem and things like that. > > > > That would solve the "atomicity" issue the WARN tracepoint solution has, > > > > and it would allow for very flexible userspace policy. > > > > > > > > I actually wonder if the existing panic_on_* sites should serve as a > > > > guide for where to put the hooks. The current sysctls could be replaced > > > > by the hooks and a simple LSM. > > > Do you really want to make error handling a "security" issue? > > > If you add security_bug(), security_warn_on() and the like > > > you're begging that they be included in SELinux (AppArmor) policy. > > > BPF, too, come to think of it. Is that what you want? > > Yeah, that is what I was thinking. This would give the LSM a view into > > kernel state, which seems a reasonable thing to do. If system integrity > > is compromised, an LSM may want to stop trusting things. > > How are you planning to communicate the security relevance of the > warning to the LSM? I don't think that __FILE__, __LINE__ or __func__ > is great information to base security policy on. Nor is a backtrace. I think that would be part of the design proposal. Initially, the known parts are "warn or bug" and "pid". > > A dedicated error-handling LSM could be added for those hooks that > > implemented the existing default panic_on_* sysctls, and could expand on > > that logic for other actions. > > I can see having an interface like LSM for choosing a bug/warn policy. > I worry about expanding the LSM hook list for a case where I would > hope no existing LSM would use them, and the new LSM doesn't use any > of the existing hooks. Yeah, I can see that, though we've got a history of the "specialized" hooks getting used by other LSMs. (e.g. loadpin's stuff got hooked up to other LSMs, etc.) -- Kees Cook
