On Thu, 23 Feb 2017 19:30:02 +0100 Peter Zijlstra <[email protected]> wrote:
> Hi Masami, > > I just wondered what would happen if I put a probe on an instruction > that was listed in __ex_table[] or __bug_table[]. Ah, thanks for reporting, I know __ex_table issue and fixed, but I didn't care about __bug_table. > And it looks like it will happily do that. It will then run the > instruction out-of-line, and when said instruction traps, the > instruction address will not match the one listed in either __ex_table[] > or __bug_table[] and badness will happen. For the __ex_table[], at least on x86, kprobes already handles it in kprobe_fault_handler, which restore regs->ip to original place when a pagefault happens on singlestepping. > If kprobes does indeed not check this, we should probably fix it, if it > does do check this, could you point me to it? Yeah, for BUG() case, as far as I can see, there is no check about that. So, there are 2 ways to fix it up, one is to just reject to put kprobes on UD2, another is fixup trap address as we did for exceptions_table. I think latter is better because if there is a divide error happening on single-step, anyway we should fixup the address... Thank you, -- Masami Hiramatsu <[email protected]>
