On Tue, May 9, 2017 at 4:10 AM, Greg KH <greg@xxxxxxxxx> wrote: > On Tue, May 09, 2017 at 08:56:19AM +0200, Ingo Molnar wrote: >> >> * Kees Cook <keescook@xxxxxxxxxxxx> wrote: >> >> > > There's the option of using GCC plugins now that the infrastructure was >> > > upstreamed from grsecurity. It can be used as part of the regular build >> > > process and as long as the analysis is pretty simple it shouldn't hurt compile >> > > time much. >> > >> > Well, and that the situation may arise due to memory corruption, not from >> > poorly-matched set_fs() calls, which static analysis won't help solve. We need >> > to catch this bad kernel state because it is a very bad state to run in. >> >> If memory corruption corrupted the task state into having addr_limit set to >> KERNEL_DS then there's already a fair chance that it's game over: it could also >> have set *uid to 0, or changed a sensitive PF_ flag, or a number of other >> things... >> >> Furthermore, think about it: there's literally an infinite amount of corrupted >> task states that could be a security problem and that could be checked after every >> system call. Do we want to check every one of them? > > Ok, I'm all for not checking lots of stuff all the time, just to protect > from crappy drivers that. Especially as we _can_ audit and run checks > on the source code for them in the kernel tree. > > But, and here's the problem, outside of the desktop/enterprise world, > there are a ton of out-of-tree code that is crap. The number of > security/bug fixes and kernel crashes for out-of-tree code in systems > like Android phones is just so high it's laughable. > > When you have a device that is running 3.2 million lines of kernel code, > yet the diffstat of the tree compared to mainline adds 3 million lines > of code, there is bound to be a ton of issues/problems there. > > So this is an entirely different thing we need to try to protect > ourselves from. A long time ago I laughed when I saw that Microsoft had > to do lots of "hardening" of their kernel to protect themselves from > crappy drivers, as I knew we didn't have to do that because we had the > source for them and could fix the root issues. But that has changed and > now we don't all have that option. That code is out-of-tree because the > vendor doesn't care, and doesn't want to take any time at all to do > anything resembling a real code review[1]. That's a big part of why I thought would be useful. I am less worried about edge cases upstream right now than forks with custom codes not using set_fs correctly. > > So, how about options like the ones being proposed here, go behind a new > config option: > CONFIG_PROTECT_FROM_CRAPPY_DRIVERS > that device owners can enable if they do not trust their vendor-provided > code (hint, I sure don't.) That way the "normal" path that all of us > are used to running will be fine, but if you want to take the speed hit > to try to protect yourself, then you can do that as well. Maybe another name but why not. > > Anyway, just an idea... > > thanks, > > greg k-h > > [1] I am working really hard with lots of vendors to try to fix their > broken development model, but that is going to take years to resolve > as their device pipelines are years long, and changing their > mindsets takes a long time... -- Thomas -- To unsubscribe from this list: send the line "unsubscribe linux-s390" in the body of a message to majordomo@xxxxxxxxxxxxxxx More majordomo info at http://vger.kernel.org/majordomo-info.html
