Consider the ring protection scheme in MULTICS.If we were to implement the system calls of a typical operating system and store them in a segment associated with ring 0,what should be the values stored in the ring field of the segment descriptor? What happens during a system call when a process executing in a higher-numbered ring invokes a procedure in ring 0?
问题信息
-
扫描二维码，关注牛客网
- 意见反馈
-
下载牛客APP，随时随地刷题
扫一扫，把题目装进口袋
- 求职之前，先上牛客
-
扫描二维码，进入QQ群
扫描二维码，关注牛客公众号
- 公司地址：北京市朝阳区北苑路北美国际商务中心K2座一层-北京牛客科技有限公司
- 联系方式：010-60728802 投诉举报电话：010-57596212（朝阳人力社保局）
- 牛客科技© All rights reserved admin@nowcoder.com
- 京ICP备14055008号-4 增值电信业务经营许可证 营业执照 人力资源服务许可证
-
京公网安备
11010502036488号
The ring should be associated with an access bracket (b1,b2),a limit value b3,and a set of designated entry points.The processes that are allowed to invoke any code stored in segment 0 in an unconstrained manner are those processes that arecurrently executing in ring i where b1≤i ≤b2 .Any other process executing within ring b2 < i≤b3 is allowed to invoke only those functions that are designated entry points.This implies that we should have b1= 0 and set b2 to be the highest ring number that comprises of system code that is allowed to invoke the code in segment 0 in an unconstrained fashion.We should also store only the system call functions as designated entry points and we should set b3 to be the ring number associated with user code so that user code can invoke the system calls.