[PATCH V32 21/27] Lock down tracing and perf kprobes when in confidentiality mode

[Matthew Garrett]

From: David Howells <dhowells at redhat.com>

Disallow the creation of perf and ftrace kprobes when the kernel is
locked down in confidentiality mode by preventing their registration.
This prevents kprobes from being used to access kernel memory to steal
crypto data, but continues to allow the use of kprobes from signed
modules.

Reported-by: Alexei Starovoitov <alexei.starovoitov at gmail.com>
Signed-off-by: David Howells <dhowells at redhat.com>
Signed-off-by: Matthew Garrett <mjg59 at google.com>
Cc: Naveen N. Rao <naveen.n.rao at linux.ibm.com>
Cc: Anil S Keshavamurthy <anil.s.keshavamurthy at intel.com>
Cc: davem at davemloft.net
Cc: Masami Hiramatsu <mhiramat at kernel.org>
---
 kernel/trace/trace_kprobe.c | 3 +++
 1 file changed, 3 insertions(+)

diff --git a/kernel/trace/trace_kprobe.c b/kernel/trace/trace_kprobe.c
index d5fb09ebba8b..5c70acd80344 100644
--- a/kernel/trace/trace_kprobe.c
+++ b/kernel/trace/trace_kprobe.c
@@ -420,6 +420,9 @@ static int __register_trace_kprobe(struct trace_kprobe *tk)
 {
 	int i, ret;
 
+	if (kernel_is_locked_down("Use of kprobes", LOCKDOWN_CONFIDENTIALITY))
+		return -EPERM;
+
 	if (trace_probe_is_registered(&tk->tp))
 		return -EINVAL;
 
-- 
2.21.0.392.gf8f6787159e-goog