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We are doing a little project that involves monitoring the Guest OS (for example Linux) from the hypervisor layer (i.e. QEMU). One of the things that we want to monitor is network traffic going in/out of the Guest OS. Is it possible to do so without modifying the Guest OS?
One way to do it is to intercept the relevant syscalls which are made when sockets are created and fetch the values from the relevant registers as the instructions are being executed. But we are not too sure if it is easy or if its the right way to do it.
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To capture network traffic, you can use tcpdump. This is a packet sniffer that can observe and record network traffic on an interface. In the following example, we capture 1,000 packets using tcpdump. An easier way to analyze network traffic is to use an actual network traffic analyzer, such as Wireshark.
So to conclude: QEMU is a type 2 hypervisor that runs within user space and performs virtual hardware emulation, whereas KVM is a type 1 hypervisor that runs in kernel space, that allows a user space program access to the hardware virtualization features of various processors.
September 2022) QEMU is a free and open-source emulator (Quick EMUlator). It emulates the machine's processor through dynamic binary translation and provides a set of different hardware and device models for the machine, enabling it to run a variety of guest operating systems.
Qemu is a machine emulator that can run operating systems and programs for one machine on a different machine. Mostly it is not used as emulator but as virtualizer in collaboration with KVM kernel components. In that case it utilizes the virtualization technology of the hardware to virtualize guests.
In addition to @usr57368 answer - For devices created with ’-netdev’, use ’-object filter-dump,...’ instead -net dump:
-object filter-dump,id=id,netdev=dev,file=filename][,maxlen=len]
Dump the network traffic on netdev dev to the file specified by filename. At most len bytes (64k by default) per packet are stored. The file format is libpcap, so it can be analyzed with tools such as tcpdump or Wireshark.
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