Re: [PATCH] prctl,x86 Add PR_[GET|SET]_CPUID for controlling the CPUID instruction.

[Jann Horn]

On Mon, Sep 12, 2016 at 09:56:11AM -0700, Andy Lutomirski wrote:
> On Sep 11, 2016 5:29 PM, "Kyle Huey" <me@xxxxxxxxxxxx> wrote:
> >
> > rr (http://rr-project.org/), a userspace record-and-replay reverse-
> > execution debugger, would like to trap and emulate the CPUID instruction.
> > This would allow us to a) mask away certain hardware features that rr does
> > not support (e.g. RDRAND) and b) enable trace portability across machines
> > by providing constant results.
> >
> > Intel supports faulting on the CPUID instruction in newer processors. Bit
> > 31 of MSR_PLATFORM_INFO advertises support for this feature. It is
> > documented in detail in Section 2.3.2 of
> > http://www.intel.com/content/dam/www/public/us/en/documents/application-notes/virtualization-technology-flexmigration-application-note.pdf.
[...]
> If this bit is preserved on fork(), then no_new_privs must be checked
> (or it must be cleared on "unsafe" exec, but that's nasty).

I think you mean "preserved on execve()"?