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SubjectRe: [PATCH v3 0/2] livepatch: Allocate and free shadow variables more safely
On Mon, Apr 16, 2018 at 01:36:45PM +0200, Petr Mladek wrote:
> 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

Acked-by: Josh Poimboeuf <>


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