[PATCH ebpf] bpf: Disallow unprivileged bpf by default

[Pawan Gupta <pawan.kumar.gupta@linux.intel.com>]

Disabling unprivileged BPF by default would help prevent unprivileged
users from creating the conditions required for potential speculative
execution side-channel attacks on affected hardware as demonstrated by
[1][2][3].

This will sync mainline with what most distros are currently applying.
An admin can enable this at runtime if necessary.

Signed-off-by: Pawan Gupta <pawan.kumar.gupta@linux.intel.com>

[1] https://access.redhat.com/security/cve/cve-2019-7308
[2] https://cve.mitre.org/cgi-bin/cvename.cgi?name=CVE-2021-3490
[3] https://bugzilla.redhat.com/show_bug.cgi?id=1672355#c5
---
 kernel/bpf/Kconfig | 5 +++++
 1 file changed, 5 insertions(+)

diff --git a/kernel/bpf/Kconfig b/kernel/bpf/Kconfig
index a82d6de86522..73d446294455 100644
--- a/kernel/bpf/Kconfig
+++ b/kernel/bpf/Kconfig
@@ -64,6 +64,7 @@ config BPF_JIT_DEFAULT_ON
 
 config BPF_UNPRIV_DEFAULT_OFF
 	bool "Disable unprivileged BPF by default"
+	default y
 	depends on BPF_SYSCALL
 	help
 	  Disables unprivileged BPF by default by setting the corresponding
@@ -72,6 +73,10 @@ config BPF_UNPRIV_DEFAULT_OFF
 	  disable it by setting it to 1 (from which no other transition to
 	  0 is possible anymore).
 
+	  Unprivileged BPF can be used to exploit potential speculative
+	  execution side-channel vulnerabilities on affected hardware. If you
+	  are concerned about it, answer Y.
+
 source "kernel/bpf/preload/Kconfig"
 
 config BPF_LSM
-- 
2.31.1