objtool/klp: Fix symbol resolution for duplicate data symbols

find_sympos() calculates a sympos used by livepatch to disambiguate
duplicately-named symbols.  For function symbols, there's a hack which
counts .text.unlikely symbols before other .text symbols, matching the
linker script's section ordering.

Not only is the hack fragile, data symbols can have the same problem.
So for example, adding a reference to pwq_cache in
ep_unregister_pollwait() can trigger a corrupt sympos and a relocation
to the wrong pwq_cache symbol in the livepatch module, resulting in a
crash or undefined behavior.

Remove the existing hack in favor of a fully deterministic solution,
using the new .klp.symid table to derive the symbol-to-id mapping from
the original vmlinux.o and the id-to-address mapping from the
corresponding vmlinux, which can then be used to determine the exact
sympos associated with the original vmlinux.

Modules don't need any special treatment: the .ko has the same
section/symbol ordering as the original whole-archive symbol table.

Fixes: dd590d4d57eb ("objtool/klp: Introduce klp diff subcommand for diffing object files")
Reported-by: Ben Procknow <bprockno@redhat.com>
Reported-by: Joe Lawrence <joe.lawrence@redhat.com>
Signed-off-by: Josh Poimboeuf <jpoimboe@kernel.org>
Signed-off-by: Ingo Molnar <mingo@kernel.org>
Cc: live-patching@vger.kernel.org
Link: https://lore.kernel.org/20260710153042.3156788-1-joe.lawrence@redhat.com
Link: https://lore.kernel.org/20260724221730.3126529-1-joe.lawrence@redhat.com
Link: https://patch.msgid.link/919785e3bf2245db02ff6391e735d9cb139170b1.1785727106.git.jpoimboe@kernel.org

1 files changed, 5 insertions, 0 deletions

diff --git a/tools/objtool/include/objtool/klp.h b/tools/objtool/include/objtool/klp.h
index 4d3c3bd462aa..0118c2c170c3 100644
--- a/tools/objtool/include/objtool/klp.h
+++ b/tools/objtool/include/objtool/klp.h
@@ -43,9 +43,14 @@ struct klp_symid {
 };
 
 struct objtool_file;
+struct elf;
+struct symbol;
 
 int klp_create_symid_sections(struct objtool_file *file);
 
+int klp_sympos_init(struct elf *orig);
+unsigned long klp_find_sympos(struct elf *elf, struct symbol *sym);
+
 int cmd_klp_checksum(int argc, const char **argv);
 int cmd_klp_diff(int argc, const char **argv);
 int cmd_klp_post_link(int argc, const char **argv);