linux-kernel - [PATCH V37 22/29] Lock down tracing and perf kprobes when in confidentiality mode

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Message-Id: <20190731221617.234725-23-matthewgarrett@google.com>
Date:   Wed, 31 Jul 2019 15:16:10 -0700
From:   Matthew Garrett <matthewgarrett@...gle.com>
To:     jmorris@...ei.org
Cc:     linux-security-module@...r.kernel.org,
        linux-kernel@...r.kernel.org, linux-api@...r.kernel.org,
        David Howells <dhowells@...hat.com>,
        Alexei Starovoitov <alexei.starovoitov@...il.com>,
        Matthew Garrett <mjg59@...gle.com>,
        Masami Hiramatsu <mhiramat@...nel.org>,
        Kees Cook <keescook@...omium.org>,
        "Naveen N . Rao" <naveen.n.rao@...ux.ibm.com>,
        Anil S Keshavamurthy <anil.s.keshavamurthy@...el.com>,
        davem@...emloft.net
Subject: [PATCH V37 22/29] Lock down tracing and perf kprobes when in
 confidentiality mode

From: David Howells <dhowells@...hat.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@...il.com>
Signed-off-by: David Howells <dhowells@...hat.com>
Signed-off-by: Matthew Garrett <mjg59@...gle.com>
Acked-by: Masami Hiramatsu <mhiramat@...nel.org>
Reviewed-by: Kees Cook <keescook@...omium.org>
Cc: Naveen N. Rao <naveen.n.rao@...ux.ibm.com>
Cc: Anil S Keshavamurthy <anil.s.keshavamurthy@...el.com>
Cc: davem@...emloft.net
Cc: Masami Hiramatsu <mhiramat@...nel.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 f0cffd0977d3..987d8427f091 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 9d483ad9bb6c..d5fbade68b33 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 <asm/setup.h>  /* for COMMAND_LINE_SIZE */
 
@@ -389,6 +390,10 @@ static int __register_trace_kprobe(struct trace_kprobe *tk)
 {
 	int i, ret;
 
+	ret = security_locked_down(LOCKDOWN_KPROBES);
+	if (ret)
+		return ret;
+
 	if (trace_kprobe_is_registered(tk))
 		return -EINVAL;
 
diff --git a/security/lockdown/lockdown.c b/security/lockdown/lockdown.c
index c050b82c7f9f..6b123cbf3748 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",
 };
 
-- 
2.22.0.770.g0f2c4a37fd-goog