** 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
+ $ cat kprobe.bt
+ kprobe:do_nanosleep { printf("task sleeping...\n"); exit(); }
+ $ cat open.bt
tracepoint:syscalls:sys_enter_openat {
- printf("filename: [%s]; flags: [%d]\n",
- str(args->filename), args->flags);
+ 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 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
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https://bugs.launchpad.net/bugs/1863234
Title:
Disabling bpf() syscall on kernel lockdown break apps when secure boot
is on
Status in linux package in Ubuntu:
Invalid
Status in linux source package in Disco:
In Progress
Status in linux source package in Eoan:
In Progress
Bug description:
[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"); exit(); }
$ 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 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
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