[kpatch] Correlating unchanged locals

[Evgenii Shatokhin]

Hi,

It might be not a problem in Kpatch itself but perhaps you could give an 
advice on how to deal with it.

I hit a strange problem when experimenting with the patches for 
CVE-2015-7872 and CVE-2016-5696 for the kernel 3.10.0-327.4.4 in CentOS.

To build the binary patch for these, I used the same GCC as was used for 
the kernel, GCC 4.8.3 20140911 (Red Hat 4.8.3-9).

The following error was reported by kpatch-build:

/usr/libexec/kpatch/create-diff-object: ERROR: gc.o: 
kpatch_create_dynamic_rela_sections: 2659: lookup_local_symbol 
graveyard.20319 (gc.c) needed for .text.key_gc_unused_keys.constprop.1

The kernel has such symbol but with a different numeric suffix:
$ readelf -sW ./vmlinux | grep -F graveyard.
  24328: ffffffff819df280    16 OBJECT  LOCAL  DEFAULT   15 graveyard.20316

I cannot say why the same GCC behaved differently in these cases.

I can change lookup_local_symbol() so that it would ignore such suffixes 
for variables (but not for the functions) when matching the names. This 
is not enough however, because the dynrela for that symbol still refers 
to graveyard.20319 and the binary patch fails to load as a result.

The problem has not shown up for other kernels so far, only for 
3.10.0-327.4.4.

Any ideas?

Regards,
Evgenii