linux: enable BPF_UNPRIV_DEFAULT_OFF between 5.10 and 5.15

Disable unprivileged access to BPF syscalls to prevent denial of service
and privilege escalation via

a) potential speculative execution side-channel-attacks on unmitigated
hardware[0]

or

b) unvalidated memory access in ringbuffer helper functions[1].

Fixes: CVE-2021-4204, CVE-2022-23222

[0] https://ebpf.io/summit-2021-slides/eBPF_Summit_2021-Keynote-Daniel_Borkmann-BPF_and_Spectre.pdf
[1] https://www.openwall.com/lists/oss-security/2022/01/13/1

nixos/doc/manual/from_md/release-notes/rl-2111.section.xml

@@ -1420,6 +1420,15 @@ Superuser created successfully.
           for those who want to have all RetroArch cores available.
         </para>
       </listitem>
+      <listitem>
+        <para>
+          The Linux kernel for security reasons now restricts access to
+          BPF syscalls via <literal>BPF_UNPRIV_DEFAULT_OFF=y</literal>.
+          Unprivileged access can be reenabled via the
+          <literal>kernel.unprivileged_bpf_disabled</literal> sysctl
+          knob.
+        </para>
+      </listitem>
     </itemizedlist>
   </section>
   <section xml:id="sec-release-21.11-notable-changes">

nixos/doc/manual/release-notes/rl-2111.section.md

@@ -417,6 +417,8 @@ In addition to numerous new and upgraded packages, this release has the followin
 
 - `retroArchCores` has been removed. This means that using `nixpkgs.config.retroarch` to customize RetroArch cores is not supported anymore. Instead, use package overrides, for example: `retroarch.override { cores = with libretro; [ citra snes9x ]; };`. Also, `retroarchFull` derivation is available for those who want to have all RetroArch cores available.
 
+- The Linux kernel for security reasons now restricts access to BPF syscalls via `BPF_UNPRIV_DEFAULT_OFF=y`. Unprivileged access can be reenabled via the `kernel.unprivileged_bpf_disabled` sysctl knob.
+
 ## Other Notable Changes {#sec-release-21.11-notable-changes}
 
 

pkgs/os-specific/linux/kernel/common-config.nix

@@ -539,6 +539,7 @@ let
       UPROBE_EVENT          = { optional = true; tristate = whenOlder "4.11" "y";};
       UPROBE_EVENTS         = { optional = true; tristate = whenAtLeast "4.11" "y";};
       BPF_SYSCALL           = whenAtLeast "4.4" yes;
+      BPF_UNPRIV_DEFAULT_OFF = whenBetween "5.10" "5.15" yes;
       BPF_EVENTS            = whenAtLeast "4.4" yes;
       FUNCTION_PROFILER     = yes;
       RING_BUFFER_BENCHMARK = no;