[Update: SMM driver dev advice for this from issue is here:
Bruno of Sogeti ESEC Lab has published an interesting paper with an SMM exploit, well-written with lots of background on UEFI and SMM exploits, lots of images/figures and links, definately worth reading:
SMM unchecked pointer vulnerability
Mon 30 May 2016 by Bruno
This article explains the exploitation of an SMM unchecked pointer vulnerability present in several firmwares. As this vulnerability is a memory corruption, it only applies to firmwares including the unpatched vulnerable DXE driver. It first explains the SMM mode and some of its mechanisms, then the reversing of the UEFI driver in which the vulnerability is present, then the exploitation of the vulnerability in it-self and finally a little conclusion about the impact of the vulnerability. […]
This vulnerability was initially found on two different firmwares of different OEM, both of them seem to have a lot in common. Their firmware were based on one version of the EDK implementation by Intel with several new features added. After some research it appears that both were using code provided by American Megatrends Inc. (AMI) . We contacted AMI and the OEM and got quick responses from them. We would like to thank them for working with us, especially Lenovo for coordinating with us. […]
This vulnerability allows to gain code execution in SMM. In the case of both studied firmwares the flash was not protected by the Protected Range (PR) registers, code execution in SMM allows rewriting the flash and potentially the setup of a persistent bootkit.
On January 2016 VirusTotal (VT) began to provide information on firmware images as described in their blog post . We used this for finding firmware which includes the SMIFlash driver. In total we found approximately 900 different firmwares (type:rom) which contains it, 468 of those had different versions, however it is likely that a lot of these firmwares are just different versions of one another. We have gathered the Vendor identification provided by VT for each of those firmware and got approximately 10 different constructors however 84% of the firmwares have AMI as vendor. […]