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 variables 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(-) -- 2.13.6