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Subject[PATCH v3 0/9] klp-convert livepatch build tooling
Date
Hi folks,

This is the third installment of the klp-convert tool for generating and
processing livepatch symbols for livepatch module builds. For those
following along at home, archive links to previous versions:

RFC:
https://lore.kernel.org/lkml/cover.1477578530.git.jpoimboe@redhat.com/
v2:
https://lore.kernel.org/lkml/f52d29f7-7d1b-ad3d-050b-a9fa8878faf2@redhat.com/

(Note that I don't see v2 archived at lore, but that is a link to the
most recent subthread that lore did catch.)


Livepatches may use symbols which are not contained in its own scope,
and, because of that, may end up compiled with relocations that will
only be resolved during module load. Yet, when the referenced symbols are
not exported, solving this relocation requires information on the object
that holds the symbol (either vmlinux or modules) and its position inside
the object, as an object may contain multiple symbols with the same name.
Providing such information must be done accordingly to what is specified
in Documentation/livepatch/module-elf-format.txt.

Currently, there is no trivial way to embed the required information as
requested in the final livepatch elf object. klp-convert solves this
problem in two different forms: (i) by relying on a symbol map, which is
built during kernel compilation, to automatically infer the relocation
targeted symbol, and, when such inference is not possible (ii) by using
annotations in the elf object to convert the relocation accordingly to
the specification, enabling it to be handled by the livepatch loader.

Given the above, add support for symbol mapping in the form of
Symbols.list file; add klp-convert tool; integrate klp-convert tool into
kbuild; make livepatch modules discernible during kernel compilation
pipeline; add data-structure and macros to enable users to annotate
livepatch source code; make modpost stage compatible with livepatches;
update livepatch-sample and update documentation.

The patch was tested under three use-cases:

use-case 1: There is a relocation in the lp that can be automatically
resolved by klp-convert. For example. see the saved_command_line
variable in lib/livepatch/test_klp_convert2.c.

use-case 2: There is a relocation in the lp that cannot be automatically
resolved, as the name of the respective symbol appears in multiple
objects. The livepatch contains an annotation to enable a correct
relocation. See the KLP_MODULE_RELOC / KLP_SYMPOS annotation sections
in lib/livepatch/test_klp_convert{1,2}.c.

use-case 3: There is a relocation in the lp that cannot be automatically
resolved similarly as 2, but no annotation was provided in the
livepatch, triggering an error during compilation. Reproducible by
removing the KLP_MODULE_RELOC / KLP_SYMPOS annotation sections in
lib/livepatch/test_klp_convert{1,2}.c.


Branches
--------

Since I spent some time tinkering with v2 and accumulated a bunch of
fixes, I collected them up and am posting this new version. For review
purposes, I posted two branches up to github:

1 - an expanded branch that with changes separate from the original
https://github.com/joe-lawrence/linux/commits/klp-convert-v3-expanded

2 - a squashed branch of (1) that comprises v3:
https://github.com/joe-lawrence/linux/commits/klp-convert-v3

Non-trivial commits in the expanded branch have some extra commentary
and details for debugging in the commit message that were dropped when
squashing into their respective parent commits.


TODO
----

There are a few outstanding items that I came across while reviewing v2,
but as changes started accumulating, it made sense to defer those to a
later version. I'll reply to this thread individual topics to start
discussion sub-threads for those.


Changelogs
----------

The commit changelogs were getting long, so I've moved them here for
posterity and review purposes:

livepatch: Create and include UAPI headers
v2:
- jmoreira: split up and changelog
v3:
- joe: convert to SPDX license tags

kbuild: Support for Symbols.list creation
v3:
- jmoreira: adjust for multiobject livepatch
- joe: add klpclean to PHONY
- joe: align KLP prefix

livepatch: Add klp-convert tool
v2:
- khlebnikov: use HOSTLOADLIBES_ instead of HOSTLDFLAGS: -lelf must be
at the end
- jmoreira: add support to automatic relocation conversion in
klp-convert.c, changelog
v3:
- joe: convert to SPDX license tags
- jmoreira: add rela symbol name to WARNs
- jmoreira: ignore relocations to .TOC and symbols with index 0
- joe: separate and fix valid_sympos() sympos=0 and sympos=1..n checks
- joe: fix symbol use-after-frees
- joe: fix remaining valgrind leak complaints (non-error paths only)
- joe: checkpatch nits

livepatch: Add klp-convert annotation helpers
v2:
- jmoreira: split up: move KLP_MODULE_RELOC from previous patch to
here, add KLP_SYMPOS, move macros from include/uapi/livepatch.h to
include/linux/livepatch.h
v3:
- joe: suggested by jpoimboe, KLP_MODULE_RELOC macro should 4-byte
align klp_module_reloc structures

modpost: Integrate klp-convert
v2:
- khlebnikov: save cmd_ld_ko_o into .module.cmd, if_changed_rule
doesn't do that.f
- khlebnikov: fix bashisms for debian where /bin/sh is a symlink to
/bin/dash
- khlebnikov: rename rule_link_module to rule_ld_ko_o, otherwise
arg-check inside if_changed_rule compares cmd_link_module and
cmd_ld_ko_o.
- khlebnikov: check modinfo -F livepatch only if CONFIG_LIVEPATCH is
true.
- mbenes: remove modinfo call. LIVEPATCH_ in Makefile
- jmoreira: split up: move the .livepatch file-based scheme for
identifying livepatches to a previous patch, as it was required for
correctly building Symbols.list there.
v3:
- joe: adjust rule_ld_ko_o to call echo-cmd
- joe: rebase for v5.1
- joe: align KLP prefix

modpost: Add modinfo flag to livepatch modules
v2:
- jmoreira: fix modpost.c (add_livepatch_flag) to update module
structure with livepatch flag and prevent modpost from breaking due to
unresolved symbols
v3:
- joe: adjust modpost.c::get_modinfo() call for v5.0 version

livepatch: Add sample livepatch module
v3:
- joe: update all in-tree livepatches with LIVEPATCH_* modinfo flag

documentation: Update on livepatch elf format
v2:
- jmoreira: update module to use KLP_SYMPOS
- jmoreira: Comments on symbol resolution scheme
- jmoreira: Update Makefile
- jmoreira: Remove MODULE_INFO statement
- jmoreira: Changelog
v3:
- joe: rebase for v5.1
- joe: code shuffle to better match original source file

livepatch/selftests: add klp-convert
v3:
- joe: clarify sympos=0 and sympos=1..n


And now the usual git cover-letter boilerplate...

Joao Moreira (2):
kbuild: Support for Symbols.list creation
documentation: Update on livepatch elf format

Joe Lawrence (1):
livepatch/selftests: add klp-convert

Josh Poimboeuf (5):
livepatch: Create and include UAPI headers
livepatch: Add klp-convert tool
livepatch: Add klp-convert annotation helpers
modpost: Integrate klp-convert
livepatch: Add sample livepatch module

Miroslav Benes (1):
modpost: Add modinfo flag to livepatch modules

.gitignore | 1 +
Documentation/livepatch/livepatch.txt | 3 +
Documentation/livepatch/module-elf-format.txt | 50 +-
MAINTAINERS | 2 +
Makefile | 30 +-
include/linux/livepatch.h | 13 +
include/uapi/linux/livepatch.h | 22 +
kernel/livepatch/core.c | 4 +-
lib/livepatch/Makefile | 15 +
lib/livepatch/test_klp_atomic_replace.c | 1 -
lib/livepatch/test_klp_callbacks_demo.c | 1 -
lib/livepatch/test_klp_callbacks_demo2.c | 1 -
lib/livepatch/test_klp_convert1.c | 106 +++
lib/livepatch/test_klp_convert2.c | 103 +++
lib/livepatch/test_klp_convert_mod_a.c | 25 +
lib/livepatch/test_klp_convert_mod_b.c | 13 +
lib/livepatch/test_klp_livepatch.c | 1 -
samples/livepatch/Makefile | 7 +
.../livepatch/livepatch-annotated-sample.c | 102 +++
samples/livepatch/livepatch-sample.c | 1 -
scripts/Kbuild.include | 4 +-
scripts/Makefile | 1 +
scripts/Makefile.build | 7 +
scripts/Makefile.modpost | 24 +-
scripts/livepatch/.gitignore | 1 +
scripts/livepatch/Makefile | 7 +
scripts/livepatch/elf.c | 753 ++++++++++++++++++
scripts/livepatch/elf.h | 72 ++
scripts/livepatch/klp-convert.c | 692 ++++++++++++++++
scripts/livepatch/klp-convert.h | 39 +
scripts/livepatch/list.h | 391 +++++++++
scripts/mod/modpost.c | 82 +-
scripts/mod/modpost.h | 1 +
.../selftests/livepatch/test-livepatch.sh | 64 ++
34 files changed, 2616 insertions(+), 23 deletions(-)
create mode 100644 include/uapi/linux/livepatch.h
create mode 100644 lib/livepatch/test_klp_convert1.c
create mode 100644 lib/livepatch/test_klp_convert2.c
create mode 100644 lib/livepatch/test_klp_convert_mod_a.c
create mode 100644 lib/livepatch/test_klp_convert_mod_b.c
create mode 100644 samples/livepatch/livepatch-annotated-sample.c
create mode 100644 scripts/livepatch/.gitignore
create mode 100644 scripts/livepatch/Makefile
create mode 100644 scripts/livepatch/elf.c
create mode 100644 scripts/livepatch/elf.h
create mode 100644 scripts/livepatch/klp-convert.c
create mode 100644 scripts/livepatch/klp-convert.h
create mode 100644 scripts/livepatch/list.h

--
2.20.1

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