FPGAs are newly added to the cloud to offer energy-efficient acceleration. Multi-tenancy is an emerging phenomenon in cloud FPGAs to enable resource efficiency. In a multi-tenant scenario, multiple users can share the same FPGA fabric either spatially (i.e., tenants share different resources at the same time) or temporally (tenants share the same resources in different time slots). Undesired access or manipulation of other tenant's data can cause security and safety issues. Although safety/security concepts in access control policies have been thoroughly studied in conventional cloud systems, they are relatively unknown for cloud FPGAs. Moreover, these concepts may not trivially extend to cloud FPGAs due to their different nature. This paper proposes an improved access control mechanism for multi-tenant cloud FPGAs. Compared to existing commercial tools, our solution allows dynamic configuration of access control privileges. Compared to earlier academic proposals with dynamic configuration, the results show that our proposal has three advantages: (i) enabling secure resource sharing of on-chip BRAMs to tenants, (ii) enabling safe sharing by resolving deadlocks and faulty access requests, and (iii) improvement in latency and throughput.