x86/arch_prctl: Add ARCH_[GET|SET]_CPUID

Intel supports faulting on the CPUID instruction beginning with Ivy Bridge.
When enabled, the processor will fault on attempts to execute the CPUID
instruction with CPL>0. Exposing this feature to userspace will allow a
ptracer to trap and emulate the CPUID instruction.

When supported, this feature is controlled by toggling bit 0 of
MSR_MISC_FEATURES_ENABLES. It is documented in detail in Section 2.3.2 of
https://bugzilla.kernel.org/attachment.cgi?id=243991

Implement a new pair of arch_prctls, available on both x86-32 and x86-64.

ARCH_GET_CPUID: Returns the current CPUID state, either 0 if CPUID faulting
    is enabled (and thus the CPUID instruction is not available) or 1 if
    CPUID faulting is not enabled.

ARCH_SET_CPUID: Set the CPUID state to the second argument. If
    cpuid_enabled is 0 CPUID faulting will be activated, otherwise it will
    be deactivated. Returns ENODEV if CPUID faulting is not supported on
    this system.

The state of the CPUID faulting flag is propagated across forks, but reset
upon exec.

Signed-off-by: Kyle Huey <[email protected]>
Cc: Grzegorz Andrejczuk <[email protected]>
Cc: [email protected]
Cc: Radim Krčmář <[email protected]>
Cc: Peter Zijlstra <[email protected]>
Cc: Dave Hansen <[email protected]>
Cc: Andi Kleen <[email protected]>
Cc: [email protected]
Cc: Nadav Amit <[email protected]>
Cc: Robert O'Callahan <[email protected]>
Cc: Richard Weinberger <[email protected]>
Cc: "Rafael J. Wysocki" <[email protected]>
Cc: Borislav Petkov <[email protected]>
Cc: Andy Lutomirski <[email protected]>
Cc: Len Brown <[email protected]>
Cc: Shuah Khan <[email protected]>
Cc: [email protected]
Cc: Jeff Dike <[email protected]>
Cc: Alexander Viro <[email protected]>
Cc: [email protected]
Cc: David Matlack <[email protected]>
Cc: Boris Ostrovsky <[email protected]>
Cc: Dmitry Safonov <[email protected]>
Cc: [email protected]
Cc: Paolo Bonzini <[email protected]>
Link: http://lkml.kernel.org/r/[email protected]
Signed-off-by: Thomas Gleixner <[email protected]>

fs/exec.c

@@ -1320,6 +1320,7 @@ void setup_new_exec(struct linux_binprm * bprm)
 	else
 		set_dumpable(current->mm, suid_dumpable);
 
+	arch_setup_new_exec();
 	perf_event_exec();
 	__set_task_comm(current, kbasename(bprm->filename), true);