Re: [PATCH 18/20] objtool: Add UACCESS validation

From: Peter Zijlstra
Date: Thu Mar 07 2019 - 13:48:32 EST

On Thu, Mar 07, 2019 at 09:54:14AM -0800, Linus Torvalds wrote:
> On Thu, Mar 7, 2019 at 9:41 AM Peter Zijlstra <peterz@xxxxxxxxxxxxx> wrote:
> > >
> > > What's the call site that made you go "just add __memset() to the list"?
> >
> > __asan_{,un}poinson_stack_memory()
> > kasan_{,un}poison_shadow()
> > __memset()
> Ugh. I think I almost just agree with your decision to just let that
> memset go unchecked.
> I'm not saying it's right, but it doesn't seem to be a fight worth fighting.

One think I could do; is add a filter to each function and only allow
__memset from the kasan code, and not from anywhere else.

Another thing I need to look at is why objtool only found memset_orig
(from __memset) but not memset_erms, which if I read the code right, is
a possible alternative there.

> Because AC vs KASAN in general ends up smelling like "not a fight
> worth fighting" to me. You've done a herculean job, but..

I know,.. I've been so close to doing that so many times, but it
seems like defeat, esp. since I'm so close now :-)