Re: [PATCH v2 2/3] binder: do not initialize locals passed to copy_from_user()

[Alexander Potapenko]

On Mon, Mar 2, 2020 at 6:38 PM Greg KH <gregkh@xxxxxxxxxxxxxxxxxxx> wrote:
>
> On Mon, Mar 02, 2020 at 02:04:29PM +0100, glider@xxxxxxxxxx wrote:
> > Certain copy_from_user() invocations in binder.c are known to
> > unconditionally initialize locals before their first use, like e.g. in
> > the following case:
> >
> >       struct binder_transaction_data tr;
> >       if (copy_from_user(&tr, ptr, sizeof(tr)))
> >               return -EFAULT;
> >
> > In such cases enabling CONFIG_INIT_STACK_ALL leads to insertion of
> > redundant locals initialization that the compiler fails to remove.
> > To work around this problem till Clang can deal with it, we apply
> > __no_initialize to local Binder structures.
>
> I would like to see actual benchmark numbers showing this is
> needed/useful otherwise it's going to just be random people adding this
> marking to random places with no real reason.
This were lib[hw]binder_benchmarks.
I will update patch description with benchmark data.
> thanks,
>
> greg k-h



-- 
Alexander Potapenko
Software Engineer

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