On Thu, Sep 23, 2021 at 06:34:08PM -0700, Vito Caputo wrote: > On Thu, Sep 23, 2021 at 06:16:16PM -0700, Kees Cook wrote: > > On Thu, Sep 23, 2021 at 05:22:30PM -0700, Vito Caputo wrote: > > > Instead of unwinding stacks maybe the kernel should be sticking an > > > entrypoint address in the current task struct for get_wchan() to > > > access, whenever userspace enters the kernel? > > > > wchan is supposed to show where the kernel is at the instant the > > get_wchan() happens. (i.e. recording it at syscall entry would just > > always show syscall entry.) > > > > And you have the syscall # onhand when performing the syscall entry, > no? > > The point is, if the alternative is to always get 0 from > /proc/PID/wchan when a process is sitting in ioctl(), I'd be perfectly > happy to get back sys_ioctl. I'm under the impression there's quite a > bit of vendor-specific flexibility here in terms of how precise WCHAN > is. Oh, yeah, if you're happy with syscall-level granularity, that'd be totally fine by me too. > If it's possible to preserve the old WCHAN precision I'm all for it. > But if we've become so paranoid about leaking anything about the > kernel to userspace that this is untenable, even if it just spits out > the syscall being performed that has value. I'd like to find a middle ground -- wchan has always seemed like a info leak, even with only symbols. And it doesn't help that walking the stack from outside the current task is difficult. :) -Kees -- Kees Cook
