Daniel P. Berrangé <berrange@redhat.com> writes:
On Tue, Jun 22, 2021 at 10:25:19AM +0200, Toke Høiland-Jørgensen wrote:
Jason Wang <jasowang@redhat.com> writes:
在 2021/6/22 上午11:29, Yuri Benditovich 写道:
On Mon, Jun 21, 2021 at 12:20 PM Jason Wang <jasowang@redhat.com> wrote:
在 2021/6/19 上午4:03, Andrew Melnichenko 写道:
Hi Jason,
I've checked "kernel.unprivileged_bpf_disabled=0" on Fedora, Ubuntu,
and Debian - no need permissions to update BPF maps.
How about RHEL :) ?
If I'm not mistaken, the RHEL releases do not use modern kernels yet
(for BPF we need 5.8+).
So this will be (probably) relevant for RHEL 9. Please correct me if I'm wrong.
Adding Toke for more ideas on this.
Ignore the kernel version number; we backport all of BPF to RHEL,
basically. RHEL8.4 is up to upstream kernel 5.10, feature-wise.
However, we completely disable unprivileged BPF on RHEL kernels. Also,
there's upstream commit:
08389d888287 ("bpf: Add kconfig knob for disabling unpriv bpf by default")
which adds a new value of '2' to the unprivileged_bpf_disable sysctl. I
believe this may end up being the default on Fedora as well.
So any design relying on unprivileged BPF is likely to break; I'd
suggest you look into how you can get this to work with CAP_BPF :)
QEMU will never have any capabilities. Any resources that required
privileges have to be opened by a separate privileged helper, and the
open FD then passed across to the QEMU process. This relies on the
capabilities checks only being performed at time of initial opening,
and *not* on operations performed on the already open FD.
That won't work for regular map updates either, unfortunately: you still
have to perform a bpf() syscall to update an element, and that is a
privileged operation.
You may be able to get around this by using an array map type and
mmap()'ing the map contents, but I'm not sure how well that will work
across process boundaries.
If it doesn't, I only see two possibilities: populate the map
ahead-of-time and leave it in place, or keep the privileged helper
process around to perform map updates on behalf of QEMU...