On Thu, 8 Nov 2018 08:44:37 -0600 Josh Poimboeuf <jpoimboe@xxxxxxxxxx> wrote: > On Thu, Nov 08, 2018 at 07:04:48PM +1100, Aleksa Sarai wrote: > > On 2018-11-08, Aleksa Sarai <cyphar@xxxxxxxxxx> 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. As I replied, If the stackdump is called from kretprobe event, regs->ip always points trampoline function. Otherwise (maybe from kprobe event, or panic, BUG etc.) it always be the address which the event occurs. So fixing regs->ip is correct. Thank you, -- Masami Hiramatsu <mhiramat@xxxxxxxxxx>
