On Thu, Mar 18, 2021 at 11:50 AM Nick Desaulniers <ndesaulniers@xxxxxxxxxx> wrote: > > On Thu, Mar 18, 2021 at 10:11 AM Sami Tolvanen <samitolvanen@xxxxxxxxxx> wrote: > > > > With CONFIG_CFI_CLANG, a callback function passed to > > __queue_delayed_work from a module points to a jump table entry > > defined in the module instead of the one used in the core kernel, > > which breaks function address equality in this check: > > > > WARN_ON_ONCE(timer->function != delayed_work_timer_fn); > > > > Use WARN_ON_FUNCTION_MISMATCH() instead to disable the warning > > when CFI and modules are both enabled. > > Does __cficanonical help with such comparisons? Or would that be a > very invasive change, if the concern was to try to keep these checks > in place for CONFIG_CFI_CLANG? The last time I checked, Clang ignored the __cficanonical attribute in header files, which means it would still generate a local jump table entry in each module for such functions, and the comparison here would fail. We could avoid the issue by using __cficanonical for the callback function *and* using __va_function() when we take the function address in modules, but that feels way too invasive for this particular use case. Sami
