Re: [PATCH V33 02/30] security: Add a "locked down" LSM hook

[Kees Cook <keescook@chromium.org>]

On Thu, Jun 20, 2019 at 06:19:13PM -0700, Matthew Garrett wrote:
> 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@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..b75941c811e6 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_is_locked_down(enum lockdown_reason what);

bikeshed: can this just be called "security_locked_down" without the
"is"?

-Kees

>  #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_is_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 2a6672c9e72f..17c17d4d8552 100644
> --- a/security/security.c
> +++ b/security/security.c
> @@ -2378,3 +2378,9 @@ void security_bpf_prog_free(struct bpf_prog_aux *aux)
>  	call_void_hook(bpf_prog_free_security, aux);
>  }
>  #endif /* CONFIG_BPF_SYSCALL */
> +
> +int security_is_locked_down(enum lockdown_reason what)
> +{
> +	return call_int_hook(locked_down, 0, what);
> +}
> +EXPORT_SYMBOL(security_is_locked_down);
> -- 
> 2.22.0.410.gd8fdbe21b5-goog
> 

-- 
Kees Cook