| Message ID | 20210318171111.706303-6-samitolvanen@google.com (mailing list archive) |
|---|---|
| State | New, archived |
| Headers | show |
| Series | Add support for Clang CFI | expand |
On Thu, Mar 18, 2021 at 10:11 AM Sami Tolvanen <samitolvanen@google.com> 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? > > Signed-off-by: Sami Tolvanen <samitolvanen@google.com> > --- > kernel/workqueue.c | 2 +- > 1 file changed, 1 insertion(+), 1 deletion(-) > > diff --git a/kernel/workqueue.c b/kernel/workqueue.c > index 0d150da252e8..03fe07d2f39f 100644 > --- a/kernel/workqueue.c > +++ b/kernel/workqueue.c > @@ -1630,7 +1630,7 @@ static void __queue_delayed_work(int cpu, struct workqueue_struct *wq, > struct work_struct *work = &dwork->work; > > WARN_ON_ONCE(!wq); > - WARN_ON_ONCE(timer->function != delayed_work_timer_fn); > + WARN_ON_FUNCTION_MISMATCH(timer->function, delayed_work_timer_fn); > WARN_ON_ONCE(timer_pending(timer)); > WARN_ON_ONCE(!list_empty(&work->entry)); > > -- > 2.31.0.291.g576ba9dcdaf-goog > -- Thanks, ~Nick Desaulniers
On Thu, Mar 18, 2021 at 11:50 AM Nick Desaulniers <ndesaulniers@google.com> wrote: > > On Thu, Mar 18, 2021 at 10:11 AM Sami Tolvanen <samitolvanen@google.com> 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
diff --git a/kernel/workqueue.c b/kernel/workqueue.c index 0d150da252e8..03fe07d2f39f 100644 --- a/kernel/workqueue.c +++ b/kernel/workqueue.c @@ -1630,7 +1630,7 @@ static void __queue_delayed_work(int cpu, struct workqueue_struct *wq, struct work_struct *work = &dwork->work; WARN_ON_ONCE(!wq); - WARN_ON_ONCE(timer->function != delayed_work_timer_fn); + WARN_ON_FUNCTION_MISMATCH(timer->function, delayed_work_timer_fn); WARN_ON_ONCE(timer_pending(timer)); WARN_ON_ONCE(!list_empty(&work->entry));
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. Signed-off-by: Sami Tolvanen <samitolvanen@google.com> --- kernel/workqueue.c | 2 +- 1 file changed, 1 insertion(+), 1 deletion(-)