> On Feb 15, 2019, at 4:19 PM, Steven Rostedt <rostedt@xxxxxxxxxxx> wrote: > > On Fri, 15 Feb 2019 15:49:35 -0800 > Andy Lutomirski <luto@xxxxxxxxxxxxxx> 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? > I think “kernel address” is right. It’s illegal to access anything that isn’t known to be a valid kernel address while in KERNEL_DS. The old __copy seems likely to have always been a bit bogus. BTW, what is this probe_mem_read() thing? Some minimal inspection suggests it’s a buggy reimplementation of probe_kernel_read(). Can you delete it and just use probe_kernel_read() directly? > For reference: > > http://lkml.kernel.org/r/20190215174945.557218316@xxxxxxxxxxx > http://lkml.kernel.org/r/20190215142015.860423791@xxxxxxxxxxx > > -- Steve
