Christian Brauner <brauner@xxxxxxxxxx> writes: > On Fri, Jun 30, 2023 at 01:15:47AM +0200, Toke Høiland-Jørgensen wrote: >> Andrii Nakryiko <andrii@xxxxxxxxxx> writes: >> >> > This patch set introduces new BPF object, BPF token, which allows to delegate >> > a subset of BPF functionality from privileged system-wide daemon (e.g., >> > systemd or any other container manager) to a *trusted* unprivileged >> > application. Trust is the key here. This functionality is not about allowing >> > unconditional unprivileged BPF usage. Establishing trust, though, is >> > completely up to the discretion of respective privileged application that >> > would create a BPF token, as different production setups can and do achieve it >> > through a combination of different means (signing, LSM, code reviews, etc), >> > and it's undesirable and infeasible for kernel to enforce any particular way >> > of validating trustworthiness of particular process. >> > >> > The main motivation for BPF token is a desire to enable containerized >> > BPF applications to be used together with user namespaces. This is currently >> > impossible, as CAP_BPF, required for BPF subsystem usage, cannot be namespaced >> > or sandboxed, as a general rule. E.g., tracing BPF programs, thanks to BPF >> > helpers like bpf_probe_read_kernel() and bpf_probe_read_user() can safely read >> > arbitrary memory, and it's impossible to ensure that they only read memory of >> > processes belonging to any given namespace. This means that it's impossible to >> > have namespace-aware CAP_BPF capability, and as such another mechanism to >> > allow safe usage of BPF functionality is necessary. BPF token and delegation >> > of it to a trusted unprivileged applications is such mechanism. Kernel makes >> > no assumption about what "trusted" constitutes in any particular case, and >> > it's up to specific privileged applications and their surrounding >> > infrastructure to decide that. What kernel provides is a set of APIs to create >> > and tune BPF token, and pass it around to privileged BPF commands that are >> > creating new BPF objects like BPF programs, BPF maps, etc. >> >> So a colleague pointed out today that the Seccomp Notify functionality >> would be a way to achieve your stated goal of allowing unprivileged >> containers to (selectively) perform bpf() syscall operations. Christian >> Brauner has a pretty nice writeup of the functionality here: >> https://people.kernel.org/brauner/the-seccomp-notifier-new-frontiers-in-unprivileged-container-development > > I'm amazed you read this. :) I found it quite an enjoyable read, actually :) > The seccomp notifier comes with a lot of caveats. I think it would be > impractical if not infeasible to handle bpf() delegation. Right, thank you for chiming in and explaining the context. I replied elsewhere in the thread on the content, so let's not fork the discussion any more than we have to... -Toke
