** Description changed:
+ [Impact]
+
+ The bpf(2) system call is completely blocked in Disco and Eoan when
+ Secure Boot is enabled due to overly restrictive Lockdown policies. This
+ makes it so that all bpf related tools are not usable on those releases.
+
+ [Test Case]
+
+ Set up test BPF programs:
+
+ $ cat hello.bt
+ BEGIN { printf("hello\n"); exit(); }
+ $ cat kprobe.bt
+ kprobe:do_nanosleep { printf("task sleeping...\n"); }
+ $ cat open.bt
+ tracepoint:syscalls:sys_enter_openat {
+ printf("filename: [%s]; flags: [%d]\n",
+ str(args->filename), args->flags);
+ }
+
+
+ Disable Secure Boot:
+
+ $ sudo mokutil --disable-validation
+ ...
+ $ sudo reboot
+
+ Ensure that hello.bt can run:
+
+ $ sudo bpftrace hello.bt
+ Attaching 1 probe...
+ hello
+
+ Ensure that a BPF program triggered by a kprobe works (run `sleep 1` in
another terminal):
+ $ sudo bpftrace kprobe.bt
+ Attaching 1 probe...
+ task sleeping...
+
+ Ensure that a BPF program triggered by a tracepoint can access the filename
and flags of openat(2):
+ $ sudo bpftrace open.bt
+ Attaching 1 probe...
+ filename: [/proc/2317/cmdline]; flags: [0]
+ filename: [/dev/iio:device1]; flags: [2048]
+ ...
+
+ Enable Secure Boot
+
+ $ sudo mokutil --enable-validation
+ ...
+ $ sudo reboot
+
+ Ensure that a basic BPF program can run:
+
+ $ sudo bpftrace hello.bt
+ Attaching 1 probe...
+ hello
+
+ Ensure that a BPF program triggered by a kprobe is blocked (kprobes aren't
allowed under Secure Boot):
+ $ sudo bpftrace kprobe.bt
+ Attaching 1 probe...
+ cannot attach kprobe, Operation not permitted
+ Error attaching probe: 'kprobe:do_nanosleep'
+
+ You should see the following kernel message logged:
+
+ Lockdown: bpftrace: Use of kprobes is restricted; see man
+ kernel_lockdown.7
+
+ Ensure that a BPF program triggered by a tracepoint can NOT access the
filename and flags of openat(2) (all filenames should be empty and all flags
should be 0):
+ $ sudo bpftrace open.bt
+ Attaching 1 probe...
+ filename: []; flags: [0]
+ filename: []; flags: [0]
+ ...
+
+ You should see the following kernel message logged:
+
+ Lockdown: iio-sensor-prox: BPF is restricted; see man kernel_lockdown.7
+
+ [Regression Potential]
+
+ Low. This is opening up the use of bpf(2) while under Lockdown. There
+ should be no new restrictions put in place.
+
+ [Original Report]
+
In disco and eoan, lockdown is automatically enforced when secure boot
is on [0]. Because lockdown was not in the mailine kernel at the time,
- some disto-specific patches were added to the kernel, including one that
- drastically restricts BPF usage by completely disabling the use of the
- `bpf()` system call when lockdown is on [1].
+ some disrto-specific patches were added to the kernel, including one
+ that drastically restricts BPF usage by completely disabling the use of
+ the `bpf()` system call when lockdown is on [1].
A consequence of that decision is that no application relying on eBPF
can run on 19.04/19.10, unless secure boot / lockdown is disabled. For
example, Cilium (cilium.io) strongly relies on BPF programs to implement
its datapath and securing network connectivity between containers. Other
applications like Suricata or Sysdig also rely on BPF to some extent.
None of which will work by default on a EFI machine with secure boot
activated.
If I understand correctly, kernel 5.4 (to be used in focal) will have a
different, lighter restricton (comming from mainline Linux kernel) [2],
so `bpf()` for networking use cases should mostly work on 20.04. Is my
understanding correct? If so, could this patch be backported to 19.10
(and 19.04, if still supported) instead of completely disabling the
syscall on lockdown?
Links:
[0]
https://git.launchpad.net/~ubuntu-kernel/ubuntu/+source/linux/+git/disco/commit/?id=d0db99473fc3bb8a5d03f99ed454ac7ca5e7d517
[1]
https://git.launchpad.net/~ubuntu-kernel/ubuntu/+source/linux/+git/disco/commit/?id=2a68c65abae66d28e2acb3245cb156ae2ea6eb1d
[2]
https://git.launchpad.net/~ubuntu-kernel/ubuntu/+source/linux/+git/focal/commit/?id=9d1f8be5cf42b497a3bddf1d523f2bb142e9318c
--
You received this bug notification because you are a member of Ubuntu
Bugs, which is subscribed to Ubuntu.
https://bugs.launchpad.net/bugs/1863234
Title:
Disabling bpf() syscall on kernel lockdown break apps when secure boot
is on
To manage notifications about this bug go to:
https://bugs.launchpad.net/ubuntu/+source/linux/+bug/1863234/+subscriptions
--
ubuntu-bugs mailing list
[email protected]
https://lists.ubuntu.com/mailman/listinfo/ubuntu-bugs
