[PATCH V40 22/29] lockdown: 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>
Acked-by: Masami Hiramatsu <mhiramat at kernel.org>
Reviewed-by: Kees Cook <keescook at chromium.org>
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>
Signed-off-by: James Morris <jmorris at namei.org>
---
 include/linux/security.h     | 1 +
 kernel/trace/trace_kprobe.c  | 5 +++++
 security/lockdown/lockdown.c | 1 +
 3 files changed, 7 insertions(+)

diff --git a/include/linux/security.h b/include/linux/security.h
index 669e8de5299d..0b2529dbf0f4 100644
--- a/include/linux/security.h
+++ b/include/linux/security.h
@@ -117,6 +117,7 @@ enum lockdown_reason {
 	LOCKDOWN_MMIOTRACE,
 	LOCKDOWN_INTEGRITY_MAX,
 	LOCKDOWN_KCORE,
+	LOCKDOWN_KPROBES,
 	LOCKDOWN_CONFIDENTIALITY_MAX,
 };
 
diff --git a/kernel/trace/trace_kprobe.c b/kernel/trace/trace_kprobe.c
index 7d736248a070..fcb28b0702b2 100644
--- a/kernel/trace/trace_kprobe.c
+++ b/kernel/trace/trace_kprobe.c
@@ -11,6 +11,7 @@
 #include <linux/uaccess.h>
 #include <linux/rculist.h>
 #include <linux/error-injection.h>
+#include <linux/security.h>
 
 #include "trace_dynevent.h"
 #include "trace_kprobe_selftest.h"
@@ -415,6 +416,10 @@ static int __register_trace_kprobe(struct trace_kprobe *tk)
 {
 	int i, ret;
 
+	ret = security_locked_down(LOCKDOWN_KPROBES);
+	if (ret)
+		return ret;
+
 	if (trace_probe_is_registered(&tk->tp))
 		return -EINVAL;
 
diff --git a/security/lockdown/lockdown.c b/security/lockdown/lockdown.c
index 403b30357f75..27b2cf51e443 100644
--- a/security/lockdown/lockdown.c
+++ b/security/lockdown/lockdown.c
@@ -32,6 +32,7 @@ static char *lockdown_reasons[LOCKDOWN_CONFIDENTIALITY_MAX+1] = {
 	[LOCKDOWN_MMIOTRACE] = "unsafe mmio",
 	[LOCKDOWN_INTEGRITY_MAX] = "integrity",
 	[LOCKDOWN_KCORE] = "/proc/kcore access",
+	[LOCKDOWN_KPROBES] = "use of kprobes",
 	[LOCKDOWN_CONFIDENTIALITY_MAX] = "confidentiality",
 };
 
-- 
2.23.0.rc1.153.gdeed80330f-goog