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    Subject[PATCH V37 02/29] security: Add a "locked down" LSM hook
    From
    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>
    Acked-by: Casey Schaufler <casey@schaufler-ca.com>
    ---
    include/linux/lsm_hooks.h | 2 ++
    include/linux/security.h | 32 ++++++++++++++++++++++++++++++++
    security/security.c | 6 ++++++
    3 files changed, 40 insertions(+)

    diff --git a/include/linux/lsm_hooks.h b/include/linux/lsm_hooks.h
    index aebb0e032072..29c22cf40113 100644
    --- a/include/linux/lsm_hooks.h
    +++ b/include/linux/lsm_hooks.h
    @@ -1807,6 +1807,7 @@ 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 +2047,7 @@ 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 66a2fcbe6ab0..c2b1204e8e26 100644
    --- a/include/linux/security.h
    +++ b/include/linux/security.h
    @@ -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_blocking_lsm_notifier(enum lsm_event event, void *data)
    @@ -1205,6 +1233,10 @@ 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 90f1e291c800..ce6c945bf347 100644
    --- a/security/security.c
    +++ b/security/security.c
    @@ -2392,3 +2392,9 @@ 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);
    --
    2.22.0.770.g0f2c4a37fd-goog
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