On Thu, Nov 08, 2018 at 07:04:48PM +1100, Aleksa Sarai wrote: > On 2018-11-08, Aleksa Sarai <cyp...@cyphar.com> wrote: > > I will attach what I have at the moment to hopefully explain what the > > issue I've found is (re-using the kretprobe architecture but with the > > shadow-stack idea). > > Here is the patch I have at the moment (it works, except for the > question I have about how to handle the top-level pt_regs -- I've marked > that code with XXX). > > -- > Aleksa Sarai > Senior Software Engineer (Containers) > SUSE Linux GmbH > <https://www.cyphar.com/> > > --8<--------------------------------------------------------------------- > > Since the return address is modified by kretprobe, the various unwinders > can produce invalid and confusing stack traces. ftrace mostly solved > this problem by teaching each unwinder how to find the original return > address for stack trace purposes. This same technique can be applied to > kretprobes by simply adding a pointer to where the return address was > replaced in the stack, and then looking up the relevant > kretprobe_instance when a stack trace is requested. > > [WIP: This is currently broken because the *first entry* will not be > overwritten since it looks like the stack pointer is different > when we are provided pt_regs. All other addresses are correctly > handled.]
When you see this problem, what does regs->ip point to? If it's pointing to generated code, then we don't _currently_ have a way of dealing with that. If it's pointing to a real function, we can fix that with unwind hints. -- Josh
