[PATCH v4 00/10] klp-convert livepatch build tooling

Joe Lawrence
2019-05-09T14:39:11Z

Hi all,

Thanks for the feedback to v3, I've incorporated a few more bug fixes
and style/spelling nitpicks for the series. v4 is a bit of a resting
place to collect loose ends before considering some heavier future work,
namely arch-specific special section support. See the TODO section
below for more details.

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/
v3:
https://lore.kernel.org/lkml/20190410155058.9437-1-joe.lawrence@redhat.com/

Summary
-------

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
--------

For review purposes, I posted two branches up to github:

1 - an expanded branch with changes separate from the original
https://github.com/joe-lawrence/linux/tree/klp-convert-v4-expanded

2 - a squashed branch of (1) that comprises v4:
https://github.com/joe-lawrence/linux/tree/klp-convert-v4

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
----

Summarized from the v3 thread, thanks to Miroslav, Joao and Josh for
feedback and parsing my long braindumps.

- Special (architecture specific) section support:

.altinstructions, .altinst_replacement
.parainstructions
__jump_table

We want to apply livepatch relocations *before* these sections are
processed. Or more precisely, the special section data structures
entries which directly or indirectly involve livepatch relocations.
Those need to be extracted into "klp.arch" sections, a corresponding
rela section generated, and the kernel needs supporting code to handle
deferred processing.

Note that there is already x86-arch code present for handling
.altinstruction and .parainstructions sections in
arch/x86/kernel/livepatch.c.

- Support for multiple homonym <object, name> symbols with unique
<position> values. Consider a target module with symbol table that
looks like:

29: ... FILE LOCAL DEFAULT ABS test_klp_convert_mod_a.c
32: ... FUNC LOCAL DEFAULT 3 get_homonym_string
33: ... OBJECT LOCAL DEFAULT 5 homonym_string
37: ... FILE LOCAL DEFAULT ABS test_klp_convert_mod_b.c
38: ... FUNC LOCAL DEFAULT 3 get_homonym_string
39: ... OBJECT LOCAL DEFAULT 11 homonym_string

- The BFD library is incapable of handling two rela sections with
identical sh_info values *as relocation sections*. This affects
binutils and related programs like gdb, objdump, crash utility, etc.
which fail to process klp-converted .ko files.

https://sourceware.org/bugzilla/show_bug.cgi?id=24456
https://sourceware.org/ml/binutils/2019-04/msg00194.html

Changelogs
----------

livepatch: Create and include UAPI headers
v2:
- jmoreira: split up and changelog
v3:
- joe: convert to SPDX license tags
v4:
- joe: from Masahiro, update UAPI headers with "GPL-2.0 WITH
Linux-syscall-note"
- joe: from Masahiro, types.h isn't needed by UAPI header

kbuild: Support for Symbols.list creation
v3:
- jmoreira: adjust for multiobject livepatch
- joe: add klpclean to PHONY
- joe: align KLP prefix
- joe: update all in-tree livepatches with LIVEPATCH_* modinfo flag
v4:
- joe: from Miroslav, update the samples and self-test Makefiles with
the LIVEPATCH_ build prefix.
- joe: from Artem, use $(SLIST) in klpclean and $(call cmd,livepatch)
instead of $(call cmd_livepatch)

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
v4:
- joe: spelling nits s/Insuficient/Insufficient and s/clasic/classic
- joe: from Miroslav, tweak klp-convert usage msg
- joe: don't move multiple list elements in convert_rela()
- joe: relax duplicate user symbol check

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: from Josh, KLP_MODULE_RELOC macro should 4-byte align
klp_module_reloc structures
v4:
- joe: remove the ',' struct array delimiter from KLP_SYMPOS

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
v4:
- joe: rule_ld_ko_o should include $(Q) to honor build verbosity

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
- joe: from Miroslav: remove MODULE_INFO(livepatch, "Y") from samples

livepatch: Add sample livepatch module
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

documentation: Update on livepatch elf format
v3:
- joe: clarify sympos=0 and sympos=1..n

livepatch/selftests: add klp-convert
v3 (new)
v4:
- joe: Add a ',' struct array delimiter after KLP_SYMPOS

livepatch/klp-convert: abort on special sections
v4 (new)

Git boilerplate
---------------

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

Joe Lawrence (2):
livepatch/selftests: add klp-convert
livepatch/klp-convert: abort on special sections

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 | 20 +
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 | 6 +
.../livepatch/livepatch-annotated-sample.c | 102 +++
samples/livepatch/livepatch-callbacks-demo.c | 1 -
samples/livepatch/livepatch-sample.c | 1 -
samples/livepatch/livepatch-shadow-fix1.c | 1 -
samples/livepatch/livepatch-shadow-fix2.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 | 73 ++
scripts/livepatch/klp-convert.c | 731 +++++++++++++++++
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 ++
37 files changed, 2653 insertions(+), 26 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