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

Kees Cook
2019-06-22T23:37:20Z

On Fri, Jun 21, 2019 at 05:03:31PM -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>

Acked-by: Kees Cook <keescook@chromium.org>

-Kees

> ---
> 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
>

--
Kees Cook