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Commit 9e47d31d authored by Matthew Garrett's avatar Matthew Garrett Committed by James Morris
Browse files

security: Add a "locked down" LSM hook 



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: default avatarMatthew Garrett <mjg59@google.com>
Acked-by: default avatarKees Cook <keescook@chromium.org>
Acked-by: default avatarCasey Schaufler <casey@schaufler-ca.com>
Signed-off-by: default avatarJames Morris <jmorris@namei.org>
parent e6b1db98

include/linux/lsm_hooks.h

+7 −0
Original line number Diff line number Diff line
@@ -1446,6 +1446,11 @@ 
 * @bpf_prog_free_security:

 *	Clean up the security information stored inside bpf prog.

 *

 * @locked_down

 *     Determine whether a kernel feature that potentially enables arbitrary

 *     code execution in kernel space should be permitted.

 *

 *     @what: kernel feature being accessed

 */

union security_list_options {

	int (*binder_set_context_mgr)(struct task_struct *mgr);
@@ -1807,6 +1812,7 @@ 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 {
@@ -2046,6 +2052,7 @@ 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;



/*

include/linux/security.h

+32 −0
Original line number Diff line number Diff line
@@ -77,6 +77,33 @@ enum lsm_event { 
	LSM_POLICY_CHANGE,

};



/*

 * These are reasons that can be passed to the security_locked_down()

 * LSM hook. Lockdown reasons that protect kernel integrity (ie, the

 * ability for userland to modify kernel code) are placed before

 * LOCKDOWN_INTEGRITY_MAX.  Lockdown reasons that protect kernel

 * confidentiality (ie, the ability for userland to extract

 * information from the running kernel that would otherwise be

 * restricted) are placed before LOCKDOWN_CONFIDENTIALITY_MAX.

 *

 * LSM authors should note that the semantics of any given lockdown

 * reason are not guaranteed to be stable - the same reason may block

 * one set of features in one kernel release, and a slightly different

 * set of features in a later kernel release. LSMs that seek to expose

 * lockdown policy at any level of granularity other than "none",

 * "integrity" or "confidentiality" are responsible for either

 * ensuring that they expose a consistent level of functionality to

 * userland, or ensuring that userland is aware that this is

 * potentially a moving target. It is easy to misuse this information

 * in a way that could break userspace. Please be careful not to do

 * so.

 */

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);
@@ -393,6 +420,7 @@ 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)
@@ -1210,6 +1238,10 @@ 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

security/security.c

+6 −0
Original line number Diff line number Diff line
@@ -2389,3 +2389,9 @@ 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);