Re: [PATCH] x86/suspend: fix false positive KASAN warning on suspend/resume

[Josh Poimboeuf <jpoimboe@redhat.com>]

On Thu, Dec 01, 2016 at 12:05:34PM +0300, Andrey Ryabinin wrote:
> 
> 
> On 12/01/2016 02:10 AM, Josh Poimboeuf wrote:
> > Resuming from a suspend operation is showing a KASAN false positive
> > warning:
> > 
> 
> > KASAN instrumentation poisons the stack when entering a function and
> > unpoisons it when exiting the function.  However, in the suspend path,
> > some functions never return, so their stack never gets unpoisoned,
> > resulting in stale KASAN shadow data which can cause false positive
> > warnings like the one above.
> > 
> > Reported-by: Scott Bauer <scott.bauer@intel.com>
> > Tested-by: Scott Bauer <scott.bauer@intel.com>
> > Signed-off-by: Josh Poimboeuf <jpoimboe@redhat.com>
> > ---
> >  arch/x86/kernel/acpi/sleep.c | 3 +++
> >  include/linux/kasan.h        | 7 +++++++
> >  2 files changed, 10 insertions(+)
> > 
> > diff --git a/arch/x86/kernel/acpi/sleep.c b/arch/x86/kernel/acpi/sleep.c
> > index 4858733..62bd046 100644
> > --- a/arch/x86/kernel/acpi/sleep.c
> > +++ b/arch/x86/kernel/acpi/sleep.c
> > @@ -115,6 +115,9 @@ int x86_acpi_suspend_lowlevel(void)
> >  	pause_graph_tracing();
> >  	do_suspend_lowlevel();
> >  	unpause_graph_tracing();
> > +
> > +	kasan_unpoison_stack_below_sp();
> > +
> 
> I think this might be too late. We may hit stale poison in the first C function called
> after resume (restore_processor_state()). Thus the shadow must be unpoisoned prior such call,
> i.e. somewhere in do_suspend_lowlevel() after .Lresume_point.

Yeah, I think you're right.  Will spin a v2.

-- 
Josh