[PATCH V34 02/29] security: Add a "locked down" LSM hook

[Matthew Garrett]

Add a mechanism to allow LSMs to make a policy decision around whether
kernel functionality that would allow tampering with or examining the
runtime state of the kernel should be permitted.

Signed-off-by: Matthew Garrett <mjg59 at google.com>
---
 include/linux/lsm_hooks.h |  2 ++
 include/linux/security.h  | 11 +++++++++++
 security/security.c       |  6 ++++++
 3 files changed, 19 insertions(+)

diff --git a/include/linux/lsm_hooks.h b/include/linux/lsm_hooks.h
index 66fd1eac7a32..df2aebc99838 100644
--- a/include/linux/lsm_hooks.h
+++ b/include/linux/lsm_hooks.h
@@ -1790,6 +1790,7 @@ union security_list_options {
 	int (*bpf_prog_alloc_security)(struct bpf_prog_aux *aux);
 	void (*bpf_prog_free_security)(struct bpf_prog_aux *aux);
 #endif /* CONFIG_BPF_SYSCALL */
+	int (*locked_down)(enum lockdown_reason what);
 };
 
 struct security_hook_heads {
@@ -2027,6 +2028,7 @@ struct security_hook_heads {
 	struct hlist_head bpf_prog_alloc_security;
 	struct hlist_head bpf_prog_free_security;
 #endif /* CONFIG_BPF_SYSCALL */
+	struct hlist_head locked_down;
 } __randomize_layout;
 
 /*
diff --git a/include/linux/security.h b/include/linux/security.h
index 1bb6fb2f1523..9eaf02e70707 100644
--- a/include/linux/security.h
+++ b/include/linux/security.h
@@ -76,6 +76,12 @@ enum lsm_event {
 	LSM_POLICY_CHANGE,
 };
 
+enum lockdown_reason {
+	LOCKDOWN_NONE,
+	LOCKDOWN_INTEGRITY_MAX,
+	LOCKDOWN_CONFIDENTIALITY_MAX,
+};
+
 /* These functions are in security/commoncap.c */
 extern int cap_capable(const struct cred *cred, struct user_namespace *ns,
 		       int cap, unsigned int opts);
@@ -389,6 +395,7 @@ void security_inode_invalidate_secctx(struct inode *inode);
 int security_inode_notifysecctx(struct inode *inode, void *ctx, u32 ctxlen);
 int security_inode_setsecctx(struct dentry *dentry, void *ctx, u32 ctxlen);
 int security_inode_getsecctx(struct inode *inode, void **ctx, u32 *ctxlen);
+int security_locked_down(enum lockdown_reason what);
 #else /* CONFIG_SECURITY */
 
 static inline int call_lsm_notifier(enum lsm_event event, void *data)
@@ -1189,6 +1196,10 @@ static inline int security_inode_getsecctx(struct inode *inode, void **ctx, u32
 {
 	return -EOPNOTSUPP;
 }
+static inline int security_locked_down(enum lockdown_reason what)
+{
+	return 0;
+}
 #endif	/* CONFIG_SECURITY */
 
 #ifdef CONFIG_SECURITY_NETWORK
diff --git a/security/security.c b/security/security.c
index 487e1f3eb2df..553f50e9a106 100644
--- a/security/security.c
+++ b/security/security.c
@@ -2382,3 +2382,9 @@ void security_bpf_prog_free(struct bpf_prog_aux *aux)
 	call_void_hook(bpf_prog_free_security, aux);
 }
 #endif /* CONFIG_BPF_SYSCALL */
+
+int security_locked_down(enum lockdown_reason what)
+{
+	return call_int_hook(locked_down, 0, what);
+}
+EXPORT_SYMBOL(security_locked_down);
-- 
2.22.0.410.gd8fdbe21b5-goog