linux-kernel - [PATCH v3 0/2] livepatch: introduce atomic replace

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Date:   Wed, 27 Sep 2017 23:41:28 -0400
From:   Jason Baron <jbaron@...mai.com>
To:     linux-kernel@...r.kernel.org, live-patching@...r.kernel.org
Cc:     jpoimboe@...hat.com, jeyu@...nel.org, jikos@...nel.org,
        mbenes@...e.cz, pmladek@...e.com
Subject: [PATCH v3 0/2] livepatch: introduce atomic replace

Hi,

In testing livepatch, I found that when doing cumulative patches, if a patched
function is completed reverted by a subsequent patch (back to its original state)
livepatch does not revert the funtion to its original state. Specifically, if
patch A introduces a change to function 1, and patch B reverts the change to
function 1 and introduces changes to say function 2 and 3 as well, the change
that patch A introduced to function 1 is still present. This could be addressed
by first completely removing patch A (disable and then rmmod) and then inserting
patch B (insmod and enable), but this leaves an unpatched window. In discussing
this issue with Josh on the kpatch mailing list, he mentioned that we could get
'atomic replace working properly', and that is the direction of this patchset:
https://www.redhat.com/archives/kpatch/2017-June/msg00005.html

Patches:

1) livepatch: Add klp_object and klp_func dynamic iterators
A prep patch for the 'atomic replace' feature such that dynamic objects
and functions can be allocated.

2) livepatch: add atomic replace
Core feature. Note that __klp_enable_patch() calls klp_add_nops(), which
necessitated moving a bunch of existing functions before __klp_enable_patch().
So there is a bit of churn in moving functions that are not modified.

Thanks,

-Jason

v2-v3:
-refactor how the dynamic nops are calculated (Petr Mladek)
-move the creation of dynamic nops to enable/disable paths
-add klp_replaced_patches list to indicate patches that can be re-enabled
-dropped 'replaced' field
-renamed dynamic fields in klp_func, object and patch
-moved iterator implementation to kernel/livepatch/core.c
-'inherit' nop immediate flag
-update kobject_put free'ing logic (Petr Mladek)

v1-v2:                                                                                                          
-removed the func_iter and obj_iter (Petr Mladek)
-initialiing kobject structure for no_op functions using:
 klp_init_object() and klp_init_func()
-added a 'replace' field to klp_patch, similar to the immediate field
-a 'replace' patch now disables all previous patches
-tried to shorten klp_init_patch_no_ops()...
-Simplified logic klp_complete_transition (Petr Mladek)

Jason Baron (2):
  livepatch: Add dynamic klp_object and klp_func iterators
  livepatch: add atomic replace

 include/linux/livepatch.h     |  85 +++--
 kernel/livepatch/core.c       | 738 ++++++++++++++++++++++++++++++++----------
 kernel/livepatch/core.h       |   6 +
 kernel/livepatch/patch.c      |  22 +-
 kernel/livepatch/patch.h      |   4 +-
 kernel/livepatch/transition.c |  50 ++-
 6 files changed, 685 insertions(+), 220 deletions(-)

-- 
2.6.1