Existing approaches to defending Use-After-Free (UAF) exploits are usually done using static or dynamic analysis. However, both static and dynamic analysis suffer from intrinsic deficiencies. The existing static analysis is limited in handling loops, optimization of memory representation. The existing dynamic analysis, which is characterized by lacking the maintenance of pointer information, may lead to flaws that the relationships between pointers and memory cannot be precisely identified. In this work, we propose a new method called UAF-GUARD without the above barriers, in the aim to defending against UAF exploits using fine-grained memory permission management. In particular, we design a key data structure to support the fine-grained memory permission management, which can maintain more information to capture the relationship between pointers and memory. Moreover, we design code instrumentation to enable UAF-GUARD to precisely locate the position of UAF vulnerabilities to further terminate malicious programs when anomalies are detected. We implement UAF-GUARD on a 64-bit Linux system. We carry out experiments to compare UAF-GUARD with the main existing approaches. The experimental results demonstrate that UAF-GUARD is able to effectively and efficiently defend against three types of UAF exploits with acceptable space overhead and time overhead.

Ultrathin two-dimensional (2D) materials have received much attention in the past years for a wide variety of photonic applications because of their pronounced room-temperature excitonic features, leading to unique properties in terms of light-matter interaction. However, only a few studies focus on light amplification and the complex photophysics at high excitation density. The beneficial nature of strong excitonic effects on optical gain remain hence unquantified, and despite the increased binding energies of the excitonic species, it remains unclear what the involvement of 2D excitons would be in optical gain. Here, we use colloidal CdSe nanoplatelets as a model system for colloidal 2D materials and show, using a quantitative and combinatory approach to ultrafast spectroscopy, that several excitation density-dependent optical gain regimes exist. At low density, optical gain originates from excitonic molecules delivering large material gains up to 20 000 cm ^-1 with an Auger limited lifetime of a few hundred picoseconds. At increasing pair density, we observe a persistence of this excitonic gain regime and the unexpected coexistence of blue-shifted and significantly enhanced optical gain up to 10 ⁵ cm ^-1 . We show that this peculiar situation originates from a carrier cooling bottleneck at high density that limits further exciton formation from unbound charge carriers. The insulating (multi-)exciton gas is found to coexist with the conductive phase, indicating the absence of a full Mott transition. Our results shed a new light on the photophysics of excitons in strongly excited 2D materials and pave the way for the development of more efficient (broadband) optical gain media and/or high exciton density applications.

Fiber-reinforced polymer (FRP) has been increasingly applied to steel structures for structural strengthening or crack repair, given its high strength-to-weight ratio and high stiffness-to-weight ratio. Cracks in steel structures are the dominant hidden threats to structural safety. However, it is difficult to monitor structural cracks under FRP coverage and there is little related research. In this paper, a crack monitoring method for an FRP-strengthened steel structure deploying a microstrip antenna sensor is presented. A theoretical model of the dual-substrate antenna sensor with FRP is established and the sensitivity of crack monitoring is studied. The effects of the weak conductivity of carbon fiber reinforced polymers (CFRPs) on the performance of crack monitoring are analyzed via contrast experiments. The effects of FRP thickness on the performance of the antenna sensor are studied. The influence of structural strain on crack detection coupling is studied through strain–crack coupling experiments. The results indicate that the antenna sensor can detect cracks in steel structures covered by FRP (including CFRP). FRP thickness affects the antenna sensor’s performance significantly, while the effects of strain can be ignored. The results provide a new approach for crack monitoring of FRP-strengthened steel structures with extensive application prospects.