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

[Andrey Ryabinin <aryabinin@virtuozzo.com>]

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.