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    SubjectRe: [PATCH 06/17] kthread: cfi: disable callback pointer check with modules
    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

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