Confidential computing with device memory isolation
A confidential computing (CC) apparatus includes a CPU and a peripheral device. The CPU is to run a hypervisor that hosts one or more Trusted Virtual Machines (TVMs). The peripheral device is coupled to the CPU and to an external memory. The CPU includes a TVM-Monitor (TVMM), to perform management operations on the one or more TVMs, to track memory space that is allocated by the hypervisor to the peripheral device in the external memory, to monitor memory-access requests issued by the hypervisor to the memory space allocated to the peripheral device in the external memory, and to permit or deny the memory-access requests, according to a criterion.
1. A confidential computing (CC) apparatus, comprising:
a CPU, to run a hypervisor that hosts one or more Trusted Virtual Machines (TVMs); and
a network device coupled to the CPU and to an external memory, for providing network communication to the CC apparatus,
wherein the CPU comprises a TVM-Monitor (TVMM) distinct from the hypervisor to:
perform management operations on the one or more TVMs;
track allocation messages of memory space that is allocated by the hypervisor in the external memory to the TVMs, to the network device and to the hypervisor;
monitor memory-access requests issued by the network device to the external memory;
check for each monitored memory-access request issued by the network device whether the monitored memory-access request is to a memory segment allocated to the network device issuing the request in the tracked allocation messages; and
deny: (i) memory-access requests issued by the TVMs to the memory space allocated to the network device or to the memory space allocated to the hypervisor, (ii) memory-access requests issued by the network device to the memory space allocated to the TVMS or to the memory space allocated to the hypervisor, and (iii) memory-access requests issued by the hypervisor to the memory space allocated to the TVMs or to the memory space allocated to the network device.
2. The CC apparatus according to claim 1 , wherein the memory-access requests comprise Direct Memory Access (DMA) accesses to the external memory.
3. The CC apparatus according to claim 1 , wherein the TVMM is to decide whether to permit or deny a memory-access request based on (i) an address in the external memory that is accessed by the memory-access request, and (ii) an identifier that is specified in the memory-access request and identifies a software that originated the memory-access request.
4. The CC apparatus according to claim 1 , wherein the TVMM additionally tracks deallocation messages.
5. The CC apparatus according to claim 1 , wherein the TVMM updates an allocation table responsive to the tracked allocation messages, and uses the allocation table to check whether requests are to a memory segment allocated to the TVMs issuing the requests.
6. The CC apparatus according to claim 1 , wherein the TVMM monitors memory-access requests on a system bus of the CC apparatus.
7. The CC apparatus according to claim 1 , wherein the TVMM checks whether the tracked allocations collide.
8. The CC apparatus according to claim 7 , wherein the TVMM notifies a Trusted Security Environment Security Manager (TSM) when tracked allocations to TVMs collide, and aborts the CPU when a collision between tracked allocations pertains to allocation of memory to the hypervisor.
9. The CC apparatus according to claim 1 , wherein the TVMM further monitors memory-access requests issued by the hypervisor and checks whether the requests issued by the hypervisor are to a memory segment allocated to the hypervisor.
10. The CC apparatus according to claim 9 , wherein the TVMM aborts the CPU when a memory-access request is to a memory segment not allocated to the TVM issuing the request, and aborts the CPU when a request issued by the hypervisor is not to a memory segment allocated to the hypervisor.
11. The CC apparatus according to claim 1 , wherein the TVMM tracks allocation messages by monitoring system calls of the hypervisor.
12. A confidential computing (CC) method, comprising:
running, in a CPU, a hypervisor that hosts one or more Trusted Virtual Machines (TVMs); and
using a TVM-Monitor (TVMM) distinct from the hypervisor, running in the CPU:
performing management operations on the one or more TVMs;
tracking allocation messages of memory space, which is allocated in an external memory, by the hypervisor, to the TVMs, to the hypervisor and to a network device;
monitoring memory-access requests issued by the network device to the external memory;
checking for each monitored memory-access request issued by the network device whether the monitored memory-access request is to a memory segment allocated to the network device issuing the request in the tracked allocation messages; and
denying: (i) memory-access requests issued by the TVMs to the memory space allocated to the network device or to the memory space allocated to the hypervisor, (ii) memory-access requests issued by the network device to the memory space allocated to the TVMS or to the memory space allocated to the hypervisor, and (iii) memory-access requests issued by the hypervisor to the memory space allocated to the TVMs or to the memory space allocated to the network device.
13. The method according to claim 12 , wherein the memory-access requests comprise Direct Memory Access (DMA) accesses to the external memory.
14. The method according to claim 12 , wherein denying the memory-access requests comprises deciding whether to permit or deny a memory-access request based on (i) an address in the external memory that is accessed by the memory-access request, and (ii) an identifier that is specified in the memory-access request and identifies a software that originated the memory-access request.