On Fri, 15 Feb 2019 15:49:35 -0800 Andy Lutomirski <l...@amacapital.net> wrote:
> I’m missing most of the context here, but even probe_kernel_...() is > unwise for a totally untrustworthy address. It could be MMIO, for > example. True, but kprobes are used like modules, and only allowed by root. They are used to poke literally anywhere one wants. That's the entire purpose of kprobes. > > If needed, we could come up with a safe-ish helper for tracing. For > direct-map addresses, probe_kernel_...() is probably okay. Same for > the current stack. Otherwise we could walk the page tables and check > that the address is cacheable, I suppose, although this is slightly > dubious if we don’t also check MTRRs. We could also check that the PA > is in main memory, I suppose, although this may have unfortunate > interactions with the MCE code. I added you just because I wanted help getting the change log correct, as that's what Linus was complaining about. I kept using "kernel address" when the sample bug used for the patch was really a non-canonical address (as Linus said, it's just garbage. Neither kernel or user space). But I pointed out that this can also bug if the address is canonical and in the kernel address space. The old code didn't complain about non-canonical or kernel address faulting before commit 9da3f2b7405, which only talks about kernel address space faulting (which is why I only mentioned that in my messages). Would changing all the mention of "kernel address" to "non user space" be accurate? For reference: http://lkml.kernel.org/r/20190215174945.557218...@goodmis.org http://lkml.kernel.org/r/20190215142015.860423...@goodmis.org -- Steve
