Re: [PATCH v26 24/30] x86/cet/shstk: Introduce shadow stack token setup/verify routines

[Yu, Yu-cheng]

On 5/17/2021 5:14 PM, Eugene Syromiatnikov wrote:
> On Mon, May 17, 2021 at 01:55:01PM -0700, Yu, Yu-cheng wrote:
> > On 5/17/2021 12:45 AM, Borislav Petkov wrote:
> > > On Tue, Apr 27, 2021 at 01:43:09PM -0700, Yu-cheng Yu wrote:
> > > > +static inline int write_user_shstk_32(u32 __user *addr, u32 val)
> > > > +{
> > > > +	WARN_ONCE(1, "%s used but not supported.\n", __func__);
> > > > +	return -EFAULT;
> > > > +}
> > > > +#endif
> > >
> > > What is that supposed to catch? Any concrete (mis-)use cases?
> >
> > If 32-bit apps are not supported, there should be no need of 32-bit shadow
> > stack write, otherwise there is a bug.
>
> Speaking of which, I wonder what would happen if a 64-bit process makes
> a 32-bit system call (using int 0x80, for example), and gets a signal.

Yes, that's right.  Thanks!  I should have said, if neither IA32 nor X32 
is supported.

Yu-cheng