linux-kernel - [PATCH 0/2] livepatch: Allocate and free shadow variables more safely

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Date:   Tue, 13 Mar 2018 16:54:46 +0100
From:   Petr Mladek <pmladek@...e.com>
To:     Jiri Kosina <jikos@...nel.org>,
        Josh Poimboeuf <jpoimboe@...hat.com>,
        Miroslav Benes <mbenes@...e.cz>
Cc:     Joe Lawrence <joe.lawrence@...hat.com>,
        Jessica Yu <jeyu@...nel.org>, Nicolai Stange <nstange@...e.de>,
        live-patching@...r.kernel.org, linux-kernel@...r.kernel.org,
        Petr Mladek <pmladek@...e.com>
Subject: [PATCH 0/2] livepatch: Allocate and free shadow variables more safely

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().

The patchset is against the current Linus' tree.

Petr Mladek (2):
  livepatch: Initialize shadow variables by init function safely
  livepatch: Allow to unregister or free shadow data using a custom
    function

 Documentation/livepatch/shadow-vars.txt   | 42 ++++++++++++-----
 include/linux/livepatch.h                 | 23 +++++++---
 kernel/livepatch/shadow.c                 | 75 +++++++++++++++++++++----------
 samples/livepatch/livepatch-shadow-fix1.c | 44 +++++++++++++-----
 samples/livepatch/livepatch-shadow-fix2.c | 33 +++++++-------
 5 files changed, 150 insertions(+), 67 deletions(-)

-- 
2.13.6