The issue seems to be present in Xen, Windows, and Linuxes -- this suggests that, regardless of technicalities, Intel did something unwise. (Or at least didn't communicate effectively with software vendors)
"Linux actually fixed the bug in 2006, with CVE-2006-0744. [ http://cve.mitre.org/cgi-bin/cvename.cgi?name=CVE-2006-0744 ] But the description says “Linux kernel before 2.6.16.5 does not properly handle uncanonical return addresses on Intel EM64T CPUs…”, which makes it sound like something Linux-specific. It’s therefore not surprising that it attracted little notice from other operating systems."
"Linux actually fixed the bug in 2006, with CVE-2006-0744. [ http://cve.mitre.org/cgi-bin/cvename.cgi?name=CVE-2006-0744 ] But the description says “Linux kernel before 2.6.16.5 does not properly handle uncanonical return addresses on Intel EM64T CPUs…”, which makes it sound like something Linux-specific. It’s therefore not surprising that it attracted little notice from other operating systems."