| Message ID | 20210312004919.669614-7-samitolvanen@google.com (mailing list archive) |
|---|---|
| State | Superseded |
| Headers | show |
| Series | Add support for Clang CFI | expand |
On Thu, Mar 11, 2021 at 04:49:08PM -0800, Sami Tolvanen wrote: > With CONFIG_CFI_CLANG, a callback function passed to > __kthread_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 != kthread_delayed_work_timer_fn); > > Disable the warning when CFI and modules are enabled. > > Signed-off-by: Sami Tolvanen <samitolvanen@google.com> Reviewed-by: Kees Cook <keescook@chromium.org>
On Thu, Mar 11, 2021 at 04:49:08PM -0800, Sami Tolvanen wrote: > With CONFIG_CFI_CLANG, a callback function passed to > __kthread_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 != kthread_delayed_work_timer_fn); > > Disable the warning when CFI and modules are enabled. > > Signed-off-by: Sami Tolvanen <samitolvanen@google.com> > --- > kernel/kthread.c | 8 +++++++- > 1 file changed, 7 insertions(+), 1 deletion(-) > > diff --git a/kernel/kthread.c b/kernel/kthread.c > index 1578973c5740..af5fee350586 100644 > --- a/kernel/kthread.c > +++ b/kernel/kthread.c > @@ -963,7 +963,13 @@ static void __kthread_queue_delayed_work(struct kthread_worker *worker, > struct timer_list *timer = &dwork->timer; > struct kthread_work *work = &dwork->work; > > - WARN_ON_ONCE(timer->function != kthread_delayed_work_timer_fn); > + /* > + * With CFI, timer->function can point to a jump table entry in a module, you keep spewing this comment line that has exactly 81 characters and thus badly messes up read it with a normal termina everywhere. Maybe instead of fixing that in ever duplication hide the whole check in a well documented helper (which would have to be a macro due to the typing involved).
On Thu, Mar 11, 2021 at 10:13 PM Christoph Hellwig <hch@infradead.org> wrote: > > On Thu, Mar 11, 2021 at 04:49:08PM -0800, Sami Tolvanen wrote: > > With CONFIG_CFI_CLANG, a callback function passed to > > __kthread_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 != kthread_delayed_work_timer_fn); > > > > Disable the warning when CFI and modules are enabled. > > > > Signed-off-by: Sami Tolvanen <samitolvanen@google.com> > > --- > > kernel/kthread.c | 8 +++++++- > > 1 file changed, 7 insertions(+), 1 deletion(-) > > > > diff --git a/kernel/kthread.c b/kernel/kthread.c > > index 1578973c5740..af5fee350586 100644 > > --- a/kernel/kthread.c > > +++ b/kernel/kthread.c > > @@ -963,7 +963,13 @@ static void __kthread_queue_delayed_work(struct kthread_worker *worker, > > struct timer_list *timer = &dwork->timer; > > struct kthread_work *work = &dwork->work; > > > > - WARN_ON_ONCE(timer->function != kthread_delayed_work_timer_fn); > > + /* > > + * With CFI, timer->function can point to a jump table entry in a module, > > you keep spewing this comment line that has exactly 81 characters and > thus badly messes up read it with a normal termina everywhere. > > Maybe instead of fixing that in ever duplication hide the whole check in > a well documented helper (which would have to be a macro due to the > typing involved). Sure, that sounds cleaner. I'll add a helper macro in v2. Sami
diff --git a/kernel/kthread.c b/kernel/kthread.c index 1578973c5740..af5fee350586 100644 --- a/kernel/kthread.c +++ b/kernel/kthread.c @@ -963,7 +963,13 @@ static void __kthread_queue_delayed_work(struct kthread_worker *worker, struct timer_list *timer = &dwork->timer; struct kthread_work *work = &dwork->work; - WARN_ON_ONCE(timer->function != kthread_delayed_work_timer_fn); + /* + * With CFI, timer->function can point to a jump table entry in a module, + * which fails the comparison. Disable the warning if CFI and modules are + * both enabled. + */ + if (!IS_ENABLED(CONFIG_CFI_CLANG) || !IS_ENABLED(CONFIG_MODULES)) + WARN_ON_ONCE(timer->function != kthread_delayed_work_timer_fn); /* * If @delay is 0, queue @dwork->work immediately. This is for
With CONFIG_CFI_CLANG, a callback function passed to __kthread_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 != kthread_delayed_work_timer_fn); Disable the warning when CFI and modules are enabled. Signed-off-by: Sami Tolvanen <samitolvanen@google.com> --- kernel/kthread.c | 8 +++++++- 1 file changed, 7 insertions(+), 1 deletion(-)