![]() The eXpress Data Path hook is the earliest possible point in software, where the network driver receives the packet. Linux networking has three hooks where eBPF programs can be attached: If the packet is destined to be forwarded, the metadata contains the packet header information at the egress interface where the packet is constructed by retrieving the payload from memory and combined with the metadata. When a packet arrives, the payload data is put into memory and metadata (referred to as “skb”) is created from the packet headers and then manipulated to achieve the forwarding desired. Linux provides routing functionality and works in a similar manner to a router. Although you may not know it, you are already familiar with these hooks, because functions such as IPtables and tcpdump use them. Using eBPF a small program running in a protected manner can be inserted at each of those hooks. At each of these hooks, information related to that hook is available. The Linux Kernel has “hooks” where functionality can be added. We will focus on eBPF for networking, however the technology has many other uses. ![]() Here we will try to split the difference and provide a high level view in an effort to assemble the jigsaw. There is lots of marketing material from companies using it to offer many different solutions and a lesser amount of terse technical material. The SysCall types generally handle four functions: where the program can be attached, which kernel help functions can be called, whether network packet data can be accessed directly or indirectly and which object type is transmitted as a priority in a system call.Confused by Enhanced Berkeley Packet Filters, understandably so. This way, you can use system calls to directly access network packet data, for instance. This step is important to restrict which kernel functions can be called from the SysCall and which data structures can be accessed. Finally, the SysCall type is configured.However, not every pathway needs to be examined individually. This is to ensure that the Extended BPF only acts in permitted areas and does not access data outside the sandbox. Before and after an instruction is executed, the status of the eBPF system call is checked.During this process, the control flow graph (CFG) of the program is checked in order to detect unreachable instructions that are not subsequently loaded. This could otherwise result in the kernel crashing. First, it’s checked whether the system call was ended and doesn’t contain any loops.Before an eBPF SysCall loads, it has to go through a series of checks: This environment model – known as a sandbox – helps to reduce the risk that the system has an adverse effect on the kernel logic.Įxecuting system calls in the kernel is always associated with certain security and stability risks. ![]() ![]() The Extended BPF runs within an isolated environment in the kernel and is therefore executed under protection. It can securely run any applied intermediate language (byte code) during runtime (just-in-time compilation) directly in the kernel. With its many new features, the filter is known as Extended BPF – or eBPF for short. Thanks to ongoing development, BPF now operates as a universal, virtual machine directly in the kernel, where the entire organization of processes and data occurs. The around 330 Linux SysCalls include the following: This checks the access rights before confirming or denying the request. by calling up special, operational system functions – the Berkeley Filter sends requests to the kernel. In turn, it translates the instructions into machine codes, thereby enabling direct execution. In its role as interpreter, the Berkeley Filter reads the source files, analyzes them and runs instruction by instruction. As a result, the BPF executes a predefined format of instructions. In order to perform its functions, the Berkeley Packet Filter was embedded as an interpreter in machine language as part of a virtual machine. ![]()
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