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SubjectRe: [ammarfaizi2-block:paulmck/linux-rcu/pmladek.2022.06.15a 133/140] vmlinux.o: warning: objtool: __ct_user_exit+0x41: call to __kasan_check_read() leaves .noinstr.text section
On Thu, Jun 16, 2022 at 07:32:14PM +0200, Marco Elver wrote:
> On Thu, 16 Jun 2022 at 18:44, Paul E. McKenney <paulmck@kernel.org> wrote:
> [...]
> > > > > > > >> vmlinux.o: warning: objtool: __ct_user_exit+0x41: call to __kasan_check_read() leaves .noinstr.text section
> > > > > > > >> vmlinux.o: warning: objtool: __ct_user_enter+0x7f: call to __kasan_check_read() leaves .noinstr.text section
> [...]
> > > > It's due to the atomic_read()s within the noinstr function. Within
> > > > noinstr you can use arch_atomic_read() to avoid the instrumentation.
> > >
> > > Thank you, will fix!
> >
> > And please see below for an alleged fix.
>
> Looks good, if this made the above warnings go away.

Here is hoping! I will see if I can reproduce locally. ;-)

> Btw, it's not just KASAN, but arch_atomic_read() also disables KCSAN
> checking. A similar warning would have been generated in a KCSAN
> config.

Good to know, thank you! Additional local-reproduce opportunities.

> Reviewed-by: Marco Elver <elver@google.com>

Applied, thank you!

Thanx, Paul

> > ------------------------------------------------------------------------
> >
> > commit 81e24ca26ee9933bcacf67a61e3f6ae41a025442
> > Author: Paul E. McKenney <paulmck@kernel.org>
> > Date: Thu Jun 16 09:30:37 2022 -0700
> >
> > context_tracking: Use arch_atomic_read() in __ct_state for KASAN
> >
> > Context tracking's __ct_state() function can be invoked from noinstr state
> > where RCU is not watching. This means that its use of atomic_read()
> > causes KASAN to invoke the non-noinstr __kasan_check_read() function
> > from the noinstr function __ct_state(). This is problematic because
> > someone tracing the __kasan_check_read() function could get a nasty
> > surprise because of RCU not watching.
> >
> > This commit therefore replaces the __ct_state() function's use of
> > atomic_read() with arch_atomic_read(), which KASAN does not attempt to
> > add instrumention to.
> >
> > Signed-off-by: Paul E. McKenney <paulmck@kernel.org>
> > Cc: Frederic Weisbecker <frederic@kernel.org>
> > Cc: Marco Elver <elver@google.com>
> >
> > diff --git a/include/linux/context_tracking_state.h b/include/linux/context_tracking_state.h
> > index 0aecc07fb4f50..81c51e5f03143 100644
> > --- a/include/linux/context_tracking_state.h
> > +++ b/include/linux/context_tracking_state.h
> > @@ -49,7 +49,7 @@ DECLARE_PER_CPU(struct context_tracking, context_tracking);
> >
> > static __always_inline int __ct_state(void)
> > {
> > - return atomic_read(this_cpu_ptr(&context_tracking.state)) & CT_STATE_MASK;
> > + return arch_atomic_read(this_cpu_ptr(&context_tracking.state)) & CT_STATE_MASK;
> > }
> > #endif
> >

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