KASAN issues with idle / hotplug area

On Thu, Feb 18, 2016 at 11:22:24AM +0300, Andrey Ryabinin wrote:

On 02/17/2016 10:16 PM, Mark Rutland wrote:

quoted

Looking at the assembly, functions seem to get instrumented regardless
of the __no_sanitize_address annotation. The assembly of
__invoke_psci_fn_{smc,hvc} look identical, even if one has the
annotation and one does not.

In the case below, it looks like __invoke_psci_fn_hvc is storing to the
shadow area even though it's anotated with __no_sanitize_address.  Note
that the adrp symbol resolution is bogus; psci_to_linux_errno happens to
be at offset 0 in the as-yet unlinked psci.o object.

...

quoted

I also tried using __attribute__((no_sanitize_address)) directly, in
case there was some header issue, but that doesn't seem to be the case.

I'm using the Linaro 15.08 AArch64 GCC 5.1. Is anyone else able to
confirm whether they see the same? Does the same happen for x86?

Confirming, this happens on every GCC I have (including x86).
It seems that 'no_sanitize_address' in gcc removes only memory access checks
but it doesn't remove stack redzones.
I think this is wrong, e.g. clang removes instrumentation completely. I'll submit a bug.

Ok.

Unless there's some clever trickery that we can employ, the above
renders the Linux __no_sanitize_address annotation useless for this
style of code.

We should certianly call that out in the commentary in
include/linux/compiler-gcc.h.

But we need fix this in kernel.
I see two options here:
 * completely disable instrumentation for drivers/firmware/psci.c

This is somewhat overkill, and we'd also have to disable instrumentation
for arch/arm64/kernel/psci.c (for psci_suspend_finisher).

I would like to have instrumentation for everything we can safely
instrument.

This is probably the least worst option, though.

 * get back to assembly implementation

We'd also have to convert psci_suspend_finisher and psci_cpu_suspend,
the latter being generic code. That goes against the consolidation we
were aiming for.

Mark.