[PATCH v3 0/2] livepatch: Allocate and free shadow variables more safely

From: Petr Mladek
Date: Mon Apr 16 2018 - 07:37:02 EST

Nikolai started to use shadow variables and found that list_head
is not initialized correctly using the existing API.

The problem is that LIST_HEAD_INIT() set pointers to itself.
klp_shadow_alloc() then copies these pointers to another location.

It would be possible to solve this by a late initialization. But
this does not work well with klp_shadow_get_or_alloc(). Also this
behavior is error prone. Note that list_head might be hidden in
another structure, for example mutex.

I suggest to change the API and allow to initialize the shadow
variables using a custom callback. I think that we have already
talked about this but we decided to go the easier way. It seems
that it was a bad decision.

I send also patch that add a symmetric callback to the klp_shadow_free()
functions. It might be handy especially for klp_shadow_free_all().

Changes against v2:

+ Use pr_err() instead of WARN() when ctor() fails [Josh]
+ Some typos [Mirek]

Changes against v1:

+ Rename init/free callbacks to ctor/dtor
+ Misc update of comments and commit messages
+ Fix sizeof() in the sample code in shadow-vars.txt

Petr Mladek (2):
livepatch: Initialize shadow variables safely by a custom callback
livepatch: Allow to call a custom callback when freeing shadow

Documentation/livepatch/shadow-vars.txt | 41 ++++++++----
include/linux/livepatch.h | 19 ++++--
kernel/livepatch/shadow.c | 108 ++++++++++++++++++++----------
samples/livepatch/livepatch-shadow-fix1.c | 43 +++++++++---
samples/livepatch/livepatch-shadow-fix2.c | 33 ++++-----
5 files changed, 163 insertions(+), 81 deletions(-)