[seL4] Trouble accessing linux guest through tun/tap

29 Apr 2020

      Greetings,

I am working with the camkes-arm-vm qemu-arm-virt configuration. I started with the vm_minimal configuration and have added a tun/tap interface by creating the tap on my host thusly:

# ip tuntap add tap0 mode tap
# ip addr add 10.0.120.100/24 dev tap0
# ip link set dev tap0 up

I have added support for what I beleive to be the appropriate interrupts by modifying my devices.camkes file thusly:

        vm0.untyped_mmios = [
                    "0x8040000:12", // Interrupt Controller Virtual CPU interface (Virtual Machine view)
                    "0x10040000:17", // QEMU PCI MMIO
                    "0x3eff0000:16", // QEMU PCI IO ports
                    "0x40000000:29", // Linux kernel memory regions
                    ];
        vm0.dtb_irqs = [35, 36, 37, 38];

Additionally, I have modified the settings.camkes thusly:

if(${PLATFORM} STREQUAL "qemu-arm-virt")
    # force cpu
    set(QEMU_MEMORY "2048")
    set(KernelArmCPU cortex-a53 CACHE STRING "" FORCE)
    set(VmInitRdFile ON CACHE BOOL "" FORCE)
    set(VmPCISupport ON CACHE BOOL "" FORCE)
    set(VmVirtioNetArping OFF CACHE BOOL "" FORCE)
    set(VmVirtioNetVirtqueue ON CACHE BOOL "" FORCE)
    # set(qemu_sim_extra_args "-netdev tap,id=mynet0,ifname=tap0,script=no,downscript=no -device virtio-net,netdev=mynet0,mac=52:55:00:d1:55:01")
    set(qemu_sim_extra_args "-net nic,model=e1000 -netdev tap,id=mynet0,script=no,ifname=tap0 -device virtio-net,netdev=mynet0,mac=52:55:00:d1:55:01")
    set(KernelArmExportPCNTUser ON CACHE BOOL "" FORCE)
    set(KernelArmExportPTMRUser ON CACHE BOOL "" FORCE)

endif()

This results in a tunl0 interface showing up on my linux guest. However, that interface does not have a mac address associated with it. I can use ifconfig to assign an IP address on the same subnet as the corresponding tap interface on the host. However, I can’t ping between the two. I thought this might be because I have VmVitruoNetArping set to OFF. However, I get compile time errors when I turn it on. Because the tunl0 inteface does not have the mac address specied in the qemu_sim_extra_args I am unsure of how to set up an arp table entry.

Exctly what do I need to do to enable network communications between my linux guest and the host?

[seL4] Trouble accessing linux guest through tun/tap

Travis Wheatley