Re: [PATCH v26 22/30] x86/cet/shstk: Add user-mode shadow stack support

[Borislav Petkov]

On Wed, Apr 28, 2021 at 11:39:00AM -0700, Yu, Yu-cheng wrote:
> Sorry about that.  After that email thread, we went ahead to separate shadow
> stack and ibt into different files.  I thought about the struct, the file
> names cet.h, etc.  The struct still needs to include ibt status, and if it
> is shstk_desc, the name is not entirely true.  One possible approach is, we
> don't make it a struct here, and put every item directly in thread_struct.
> However, the benefit of putting all in a struct is understandable (you might
> argue the opposite :-)).  Please make the call, and I will do the change.

/me looks forward into the patchset...

So this looks like the final version of it:

@@ -15,6 +15,7 @@ struct cet_status {
 	unsigned long	shstk_base;
 	unsigned long	shstk_size;
 	unsigned int	locked:1;
+	unsigned int	ibt_enabled:1;
 };

If so, that thing should be simply:

	struct cet {
		unsigned long shstk_base;
		unsigned long shstk_size;
		unsigned int shstk_lock : 1,
			     ibt	: 1;
	}

Is that ibt flag per thread or why is it here? I guess I'll find out.

/me greps...

ah yes, it is.

> Yes, the comments are in patch #23: Handle thread shadow stack.  I wanted to
> add that in the patch that takes the path.

That comes next, I'll look there.

> > vm_munmap() can return other negative error values, where are you
> > handling those?
> > 
> 
> For other error values, the loop stops.

And then what happens?

> > > +	cet->shstk_base = 0;
> > > +	cet->shstk_size = 0;

You clear those here without even checking whether unmap failed somehow.
And then stuff leaks but we don't care, right?

Someone else's problem, I'm sure.

-- 
Regards/Gruss,
    Boris.

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