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Subject[PATCH v4 1/3] kernel/modules: Add REL24 relocation support of livepatch symbols
Date
Livepatch re-uses module loader function apply_relocate_add() to write
relocations, instead of managing them by arch-dependent
klp_write_module_reloc() function.

apply_relocate_add() doesn't understand livepatch symbols (marked with
SHN_LIVEPATCH symbol section index) and assumes them to be local symbols
by default for R_PPC64_REL24 relocation type. It fails with an error,
when trying to calculate offset with local_entry_offset():

module_64: kpatch_meminfo: REL24 -1152921504897399800 out of range!

Whereas livepatch symbols are essentially SHN_UNDEF, should be
called via stub used for global calls. This issue can be fixed by
teaching apply_relocate_add() to handle both SHN_UNDEF/SHN_LIVEPATCH
symbols via the same stub. This patch extends SHN_UNDEF code to handle
livepatch symbols too.

Signed-off-by: Kamalesh Babulal <kamalesh@linux.vnet.ibm.com>
CC: Balbir Singh <bsingharora@gmail.com>
Cc: Naveen N. Rao <naveen.n.rao@linux.vnet.ibm.com>
Cc: Josh Poimboeuf <jpoimboe@redhat.com>
Cc: Jessica Yu <jeyu@kernel.org>
Cc: Ananth N Mavinakayanahalli <ananth@linux.vnet.ibm.com>
Cc: Aravinda Prasad <aravinda@linux.vnet.ibm.com>
Cc: Torsten Duwe <duwe@lst.de>
---
arch/powerpc/kernel/module_64.c | 3 ++-
1 file changed, 2 insertions(+), 1 deletion(-)

diff --git a/arch/powerpc/kernel/module_64.c b/arch/powerpc/kernel/module_64.c
index 0b0f896..39b01fd 100644
--- a/arch/powerpc/kernel/module_64.c
+++ b/arch/powerpc/kernel/module_64.c
@@ -613,7 +613,8 @@ int apply_relocate_add(Elf64_Shdr *sechdrs,

case R_PPC_REL24:
/* FIXME: Handle weak symbols here --RR */
- if (sym->st_shndx == SHN_UNDEF) {
+ if (sym->st_shndx == SHN_UNDEF ||
+ sym->st_shndx == SHN_LIVEPATCH) {
/* External: go via stub */
value = stub_for_addr(sechdrs, value, me);
if (!value)
--
2.9.3
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