Re: [PATCH v11 25/25] x86/cet/shstk: Add arch_prctl functions for shadow stack

[Yu, Yu-cheng]

On 8/27/2020 7:08 AM, H.J. Lu wrote:
> On Thu, Aug 27, 2020 at 7:07 AM H.J. Lu <hjl.tools@xxxxxxxxx> wrote:
> > On Thu, Aug 27, 2020 at 6:36 AM Florian Weimer <fweimer@xxxxxxxxxx> wrote:
> > > * H. J. Lu:
> > >
> > > > On Thu, Aug 27, 2020 at 6:19 AM Florian Weimer <fweimer@xxxxxxxxxx> wrote:
> > > > > * Dave Martin:
> > > > >
> > > > > > You're right that this has implications: for i386, libc probably pulls
> > > > > > more arguments off the stack than are really there in some situations.
> > > > > > This isn't a new problem though.  There are already generic prctls with
> > > > > > fewer than 4 args that are used on x86.
> > > > >
> > > > > As originally posted, glibc prctl would have to know that it has to pull
> > > > > an u64 argument off the argument list for ARCH_X86_CET_DISABLE.  But
> > > > > then the u64 argument is a problem for arch_prctl as well.
> > > >
> > > > Argument of ARCH_X86_CET_DISABLE is int and passed in register.
> > >
> > > The commit message and the C source say otherwise, I think (not sure
> > > about the C source, not a kernel hacker).
> >
> > It should read:
> >
> > arch_prctl(ARCH_X86_CET_DISABLE, unsigned long features)
>
> Or
>
> arch_prctl(ARCH_X86_CET_DISABLE, unsigned int features)

Like other arch_prctl()'s, this parameter was 'unsigned long' earlier. 
The idea was, since this arch_prctl is only implemented for the 64-bit 
kernel, we wanted it to look as 64-bit only.  I will change it back to 
'unsigned long'.

Yu-cheng