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

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Date:   Mon, 16 Apr 2018 13:36:45 +0200
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 v3 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().

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