[PATCH v2 0/5] livepatch: klp-convert tool - Minimal version

Lukas Hruska
2024-05-16T13:30:23Z

Summary
-------

This is a significantly simplified version of the original klp-convert tool.
The klp-convert code has never got a proper review and also clean ups
were not easy. The last version was v7, see
https://lore.kernel.org/r/20230306140824.3858543-1-joe.lawrence@redhat.com

The main change is that the tool does not longer search for the
symbols which would need the livepatch specific relocation entry.
Also klp.symbols file is not longer needed.

Instead, the needed information is appended to the symbol declaration
via a new macro KLP_RELOC_SYMBOL(). It creates symbol with all needed
metadata. For example:

extern char *saved_command_line \
KLP_RELOC_SYMBOL(vmlinux, vmlinux, saved_command_line, 0);

would create symbol

$>readelf -r -W <compiled livepatch module>:
Relocation section '.rela.text' at offset 0x32e60 contains 10 entries:
Offset Info Type Symbol's Value Symbol's Name + Addend
[...]
0000000000000068 0000003c00000002 R_X86_64_PC32 0000000000000000 .klp.sym.rela.vmlinux.vmlinux.saved_command_line,0 - 4
[...]

The simplified klp-convert tool just transforms symbols
created by KLP_RELOC_SYMBOL() to object specific rela sections
and rela entries which would later be proceed when the livepatch
or the livepatched object is loaded.

For example, klp-convert would replace the above symbols with:

$> readelf -r -W <livepatch_module_proceed_by_klp_convert>
Relocation section '.klp.rela.vmlinux.text' at offset 0x5cb60 contains 1 entry:
Offset Info Type Symbol's Value Symbol's Name + Addend
0000000000000068 0000003c00000002 R_X86_64_PC32 0000000000000000 .klp.sym.vmlinux.saved_command_line,0 - 4

Note that similar macro was needed also in the original version
to handle more symbols of the same name (sympos).

Given the above, add klp-convert tool; integrate klp-convert tool into
kbuild; 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.

Testing
-------

The patchset selftests build and execute on x86_64, s390x, and ppc64le
for both default config (with added livepatch dependencies) and a larger
SLE-15-ish config.

Summary of changes in this minimal version v2
------------------------

- rebase for v6.9
- cleaned-up SoB chains (suggested by pmladek)
- klp-convert: remove the symbol map auto-resolving solution
- klp-convert: add macro for flagging variables inside a LP src to be resolved by this tool
- klp-convert: code simplification
- selftests: add selftest livepatching function using an external symbol

Previous versions
-----------------

RFC:
https://lore.kernel.org/r/cover.1477578530.git.jpoimboe@redhat.com/
v2:
https://lore.kernel.org/r/f52d29f7-7d1b-ad3d-050b-a9fa8878faf2@redhat.com/
v3:
https://lore.kernel.org/r/20190410155058.9437-1-joe.lawrence@redhat.com/
v4:
https://lore.kernel.org/r/20190509143859.9050-1-joe.lawrence@redhat.com/
v5:
(not posted)
https://github.com/joe-lawrence/klp-convert-tree/tree/klp-convert-v5-devel
v6:
https://lore.kernel.org/r/20220216163940.228309-1-joe.lawrence@redhat.com/
v7:
https://lore.kernel.org/r/20230306140824.3858543-1-joe.lawrence@redhat.com/
v1 minimal: