On Thu, Dec 01, 2016 at 05:51:52PM +0100, Dmitry Vyukov wrote: > On Thu, Dec 1, 2016 at 5:45 PM, Josh Poimboeuf <jpoim...@redhat.com> wrote: > > On Thu, Dec 01, 2016 at 08:58:21AM -0600, Josh Poimboeuf wrote: > >> 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.ba...@intel.com> > >> > > Tested-by: Scott Bauer <scott.ba...@intel.com> > >> > > Signed-off-by: Josh Poimboeuf <jpoim...@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. > > > > So I tried calling kasan_unpoison_task_stack_below() from > > do_suspend_lowlevel(), but it hung on the resume. Presumably because > > restore_processor_state() does some important setup which would be > > needed before calling into kasan_unpoison_task_stack_below(). For > > example, setting up the gs register. So it's a bit of a catch-22. > > > > It could probably be fixed properly by rewriting do_suspend_lowlevel() > > to call restore_processor_state() with the temporary stack before > > switching to the original stack and doing the unpoison. > > > > (And there are some other issues with do_suspend_lowlevel() and I'd love > > to try taking a scalpel to it. But I have too many knives in the air > > already to want to try to attempt that right now...) > > > > Unless somebody else wants to take a stab at it, my original patch is > > probably good enough for now, since restore_processor_state() doesn't > > seem to be triggering any KASAN warnings. > > restore_processor_state/__restore_processor_state does not seem to > have any local variables, so KASAN does not do any stack checks there.
Actually, looking at the object code, it uses a lot of stack space and has several calls to __asan_report_load*() functions. Probably due to inlining of other functions which have stack variables. > We could disable KASAN instrumentation of the file, or of particular > functions. I don't think that would be sufficient unless it were disabled for __restore_processor_state() and all the functions it calls (and the functions they call, etc), which wouldn't necessarily be straightforward. > Or we could call kasan_unpoison_shadow() on the stack range > before switching to it. I tried that already, but it hung because restore_processor_state() hadn't been called yet (the catch-22 I mentioned aboved). -- Josh