On 3/23/2020 12:44 PM, Kees Cook wrote:

On Mon, Mar 23, 2020 at 05:44:13PM +0100, KP Singh wrote:

quoted

From: KP Singh <redacted>

The bpf_lsm_ nops are initialized into the LSM framework like any other
LSM.  Some LSM hooks do not have 0 as their default return value. The
__weak symbol for these hooks is overridden by a corresponding
definition in security/bpf/hooks.c

The LSM can be enabled / disabled with CONFIG_LSM.

Signed-off-by: KP Singh <redacted>

Nice! This is super clean on the LSM side of things. :)

One note below...

quoted

Reviewed-by: Brendan Jackman <jackmanb@google.com>
Reviewed-by: Florent Revest <redacted>
---
 security/Kconfig      | 10 ++++----
 security/Makefile     |  2 ++
 security/bpf/Makefile |  5 ++++
 security/bpf/hooks.c  | 55 +++++++++++++++++++++++++++++++++++++++++++
 4 files changed, 67 insertions(+), 5 deletions(-)
 create mode 100644 security/bpf/Makefile
 create mode 100644 security/bpf/hooks.c

diff --git a/security/Kconfig b/security/Kconfig
index 2a1a2d396228..cd3cc7da3a55 100644
--- a/security/Kconfig
+++ b/security/Kconfig

@@ -277,11 +277,11 @@ endchoice
 
 config LSM
 	string "Ordered list of enabled LSMs"
-	default "lockdown,yama,loadpin,safesetid,integrity,smack,selinux,tomoyo,apparmor" if DEFAULT_SECURITY_SMACK
-	default "lockdown,yama,loadpin,safesetid,integrity,apparmor,selinux,smack,tomoyo" if DEFAULT_SECURITY_APPARMOR
-	default "lockdown,yama,loadpin,safesetid,integrity,tomoyo" if DEFAULT_SECURITY_TOMOYO
-	default "lockdown,yama,loadpin,safesetid,integrity" if DEFAULT_SECURITY_DAC
-	default "lockdown,yama,loadpin,safesetid,integrity,selinux,smack,tomoyo,apparmor"
+	default "lockdown,yama,loadpin,safesetid,integrity,smack,selinux,tomoyo,apparmor,bpf" if DEFAULT_SECURITY_SMACK
+	default "lockdown,yama,loadpin,safesetid,integrity,apparmor,selinux,smack,tomoyo,bpf" if DEFAULT_SECURITY_APPARMOR
+	default "lockdown,yama,loadpin,safesetid,integrity,tomoyo,bpf" if DEFAULT_SECURITY_TOMOYO
+	default "lockdown,yama,loadpin,safesetid,integrity,bpf" if DEFAULT_SECURITY_DAC
+	default "lockdown,yama,loadpin,safesetid,integrity,selinux,smack,tomoyo,apparmor,bpf"
 	help
 	  A comma-separated list of LSMs, in initialization order.
 	  Any LSMs left off this list will be ignored. This can be

diff --git a/security/Makefile b/security/Makefile
index 746438499029..22e73a3482bd 100644
--- a/security/Makefile
+++ b/security/Makefile

@@ -12,6 +12,7 @@ subdir-$(CONFIG_SECURITY_YAMA)		+= yama
 subdir-$(CONFIG_SECURITY_LOADPIN)	+= loadpin
 subdir-$(CONFIG_SECURITY_SAFESETID)    += safesetid
 subdir-$(CONFIG_SECURITY_LOCKDOWN_LSM)	+= lockdown
+subdir-$(CONFIG_BPF_LSM)		+= bpf
 
 # always enable default capabilities
 obj-y					+= commoncap.o

@@ -30,6 +31,7 @@ obj-$(CONFIG_SECURITY_LOADPIN)		+= loadpin/
 obj-$(CONFIG_SECURITY_SAFESETID)       += safesetid/
 obj-$(CONFIG_SECURITY_LOCKDOWN_LSM)	+= lockdown/
 obj-$(CONFIG_CGROUP_DEVICE)		+= device_cgroup.o
+obj-$(CONFIG_BPF_LSM)			+= bpf/
 
 # Object integrity file lists
 subdir-$(CONFIG_INTEGRITY)		+= integrity

diff --git a/security/bpf/Makefile b/security/bpf/Makefile
new file mode 100644
index 000000000000..c7a89a962084
--- /dev/null
+++ b/security/bpf/Makefile

@@ -0,0 +1,5 @@
+# SPDX-License-Identifier: GPL-2.0
+#
+# Copyright (C) 2020 Google LLC.
+
+obj-$(CONFIG_BPF_LSM) := hooks.o

diff --git a/security/bpf/hooks.c b/security/bpf/hooks.c
new file mode 100644
index 000000000000..68e5824868f9
--- /dev/null
+++ b/security/bpf/hooks.c

@@ -0,0 +1,55 @@
+// SPDX-License-Identifier: GPL-2.0
+
+/*
+ * Copyright (C) 2020 Google LLC.
+ */
+#include <linux/lsm_hooks.h>
+#include <linux/bpf_lsm.h>
+
+/* Some LSM hooks do not have 0 as their default return values. Override the
+ * __weak definitons generated by default for these hooks

If you wanted to avoid this, couldn't you make the default return value
part of lsm_hooks.h?

e.g.:

LSM_HOOK(int, -EOPNOTSUPP, inode_getsecurity, struct inode *inode,
	 const char *name, void **buffer, bool alloc)

If you're going to do that you'll have to keep lsm_hooks.h and security.c
default values in sync somehow. Note that the four functions you've called
out won't be using call_int_hook() after the next round of stacking. I'm not
nixing the idea, I just don't want the default return for the security_
functions defined in two places.

...

#define LSM_HOOK(RET, DEFAULT, NAME, ...)	\
	LSM_HOOK_##RET(NAME, DEFAULT, __VA_ARGS__)
...
#define LSM_HOOK_int(NAME, DEFAULT, ...)	\
noinline int bpf_lsm_##NAME(__VA_ARGS__)	\
{						\
	return (DEFAULT);			\
}

Then all the __weak stuff is gone, and the following 4 functions don't
need to be written out, and the information is available to the macros
if anyone else might ever want it.

-Kees

quoted

+ */
+noinline int bpf_lsm_inode_getsecurity(struct inode *inode, const char *name,
+				       void **buffer, bool alloc)
+{
+	return -EOPNOTSUPP;
+}
+
+noinline int bpf_lsm_inode_setsecurity(struct inode *inode, const char *name,
+				       const void *value, size_t size,
+				       int flags)
+{
+	return -EOPNOTSUPP;
+}
+
+noinline int bpf_lsm_task_prctl(int option, unsigned long arg2,
+				unsigned long arg3, unsigned long arg4,
+				unsigned long arg5)
+{
+	return -ENOSYS;
+}
+
+noinline int bpf_lsm_xfrm_state_pol_flow_match(struct xfrm_state *x,
+					       struct xfrm_policy *xp,
+					       const struct flowi *fl)
+{
+	return 1;
+}
+
+static struct security_hook_list bpf_lsm_hooks[] __lsm_ro_after_init = {
+	#define LSM_HOOK(RET, NAME, ...) LSM_HOOK_INIT(NAME, bpf_lsm_##NAME),
+	#include <linux/lsm_hook_names.h>
+	#undef LSM_HOOK
+};
+
+static int __init bpf_lsm_init(void)
+{
+	security_add_hooks(bpf_lsm_hooks, ARRAY_SIZE(bpf_lsm_hooks), "bpf");
+	pr_info("LSM support for eBPF active\n");
+	return 0;
+}
+
+DEFINE_LSM(bpf) = {
+	.name = "bpf",
+	.init = bpf_lsm_init,
+};
-- 
2.20.1