| With the progress of chip industry and the development of information technology,the information security of modern society is paid more and more attention.In the PC platform,server platform and mobile platform,all the programs and information will run in their memory,which will lead to the existence of security problems.The safe memory running relationship is the problem of whether the platform can run normally.Since the proposal of Rowhammer problem in 2014,researchers have found that there is a design defect in dynamic random access memory(SDRAM),which is called Rowhammer.The main performance of this vulnerability is: when the attacker repeatedly hammers(activate –>Precharge)an address,the two adjacent addresses will be affected,resulting in a flip,which will change the data in memory.This will enable malicious attacks to obtain special permissions,which will greatly threaten the information security of the system.The main reason for this vulnerability is the design defects of SDRAM memory.As the feature size of SDRAM becomes smaller and smaller,this vulnerability will be exposed and become more and more serious.Since the proposal of the Rowhammer problem in 2014,foreign experts and scholars have conducted in-depth research on the vulnerability,and put forward a lot of original opinions and attack and defense solutions,but the domestic research on the vulnerability is still relatively rare.Based on the above problems and facts,and with the country’s attention to the chip industry,this paper will propose a new defense circuit for the Rowhammer vulnerability attack in SDRAM,which can alleviate the Rowhammer problem in SDRAM.And build Verilog environment for a large number of simulation to verify the reliability and functionality of this circuit.Specifically,this paper mainly completes the following work(1)Analyze and summarize the attack defense methods of SDRAM,and summarize the attack methods,and use Verilog language to simulate its attack methods,and use this simulation to verify the defense ability of the defense circuit in this paper;(2)Because this defense circuit combines the probabilistic refresh mode,a new way of generating random number is proposed,that is,using the temperature sensor inside SDRAM to generate random number,so as to increase the security and unpredictability of the Rowahmmer defense circuit in SDRAM.The random number generated by this way is unpredictable and almost impossible to be reversed The problems solved by the project;(3)In this paper,a new Rowhammer defense scheme is proposed by combining the random probability refresh scheme and the counter scheme,that is,the probabilistic scheme and the deterministic scheme,and the random simulation verification is carried out according to the attack mode in 1,so as to determine its defense capability.Based on the above work and research,a new Rowhammer defense circuit for DDR4-SDRAM was finally designed.This circuit can effectively target the row hammer attack from the outside.Because the external attack will consider the relationship between attack time and efficiency,the attack on 10 different addresses at the same time will be regarded as the dividing line,and more than 10 attack addresses will be considered The attack time is too long to be practical.This defense circuit has a good defense mechanism against attacks on 8or less different addresses at the same time,with a defense probability of 100%;attacks on8-10 addresses have a great probability of refreshing them,and the defense probability is99.5%-99.7% Between;it can also defend against the situation with more than 10 addresses,but as the number of addresses increases,the probability of defense will gradually decrease.In the case of 15 addresses,the probability is 99%.To sum up,the new defense scheme of Rowhammer based on ddr4 SDRAM proposed in this paper is an excellent scheme which can effectively protect the internal information security of SDRAM and is difficult to be attacked by reverse engineering,and has good theoretical and practical significance. |
