[PATCH v5 1/1] security: Add mechanism to safely (un)load LSMs after boot time

On Sun, Apr 8, 2018 at 8:38 PM, Tetsuo Handa
[off-list ref] wrote:

Suggested changes on top of your patch:

  Replace "struct hlist_head *head" in "struct security_hook_list" with
  "const unsigned int offset" because there is no need to initialize with
  address of the immutable/mutable chains.

  Remove LSM_HOOK_INIT_MUTABLE() by embedding just offset (in bytes) from
  head of "struct security_hook_heads" into "struct security_hook_list"->offset.

  Make "struct security_hook_heads security_hook_heads" and
  "struct security_hook_heads security_hook_heads_mutable" local variables.

  Rename "struct security_hook_heads security_hook_heads" to
  "struct security_hook_heads security_mutable_hook_heads" and mark it as
  __ro_after_init.

  Add the fourth argument to security_add_hooks() which specifies to which
  chain (security_{mutable|immutable}_hook_heads) to connect.

  Make all built-in LSM modules (except SELinux if
  CONFIG_SECURITY_SELINUX_DISABLE=y) be connected to
  security_immutable_hook_heads.

  Rename __lsm_ro_after_init to __selinux_ro_after_init which is local to
  SELinux.

  Mark "struct security_hook_list"->hook const because it won't change.

  Mark "struct security_hook_list"->lsm const because none of
  security_add_hooks() callers are ready to modify the third argument.

  Remove SECURITY_HOOK_COUNT and "struct security_hook_list"->owner and
  the exception in randomize_layout_plugin.c because preventing module
  unloading won't work as expected.

Rather than completely removing the unloading code, might it make
sense to add a BUG_ON or WARN_ON, in security_delete_hooks if
allow_unload_module is false, and owner is not NULL?
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