[PATCH 4.15 112/128] powerpc/modules: Dont try to restore r2 after a sibling call

Greg Kroah-Hartman
2018-03-16T15:52:19Z

From: Josh Poimboeuf <jpoimboe@redhat.com>

[ Upstream commit b9eab08d012fa093947b230f9a87257c27fb829b ]

When attempting to load a livepatch module, I got the following error:

module_64: patch_module: Expect noop after relocate, got 3c820000

The error was triggered by the following code in
unregister_netdevice_queue():

14c: 00 00 00 48 b 14c <unregister_netdevice_queue+0x14c>
14c: R_PPC64_REL24 net_set_todo
150: 00 00 82 3c addis r4,r2,0

GCC didn't insert a nop after the branch to net_set_todo() because it's
a sibling call, so it never returns. The nop isn't needed after the
branch in that case.

Signed-off-by: Josh Poimboeuf <jpoimboe@redhat.com>
Acked-by: Naveen N. Rao <naveen.n.rao@linux.vnet.ibm.com>
Reviewed-and-tested-by: Kamalesh Babulal <kamalesh@linux.vnet.ibm.com>
Signed-off-by: Michael Ellerman <mpe@ellerman.id.au>
Signed-off-by: Sasha Levin <alexander.levin@microsoft.com>
Signed-off-by: Greg Kroah-Hartman <gregkh@linuxfoundation.org>
---
arch/powerpc/include/asm/code-patching.h | 1 +
arch/powerpc/kernel/module_64.c | 12 +++++++++++-
arch/powerpc/lib/code-patching.c | 5 +++++
3 files changed, 17 insertions(+), 1 deletion(-)

--- a/arch/powerpc/include/asm/code-patching.h
+++ b/arch/powerpc/include/asm/code-patching.h
@@ -33,6 +33,7 @@ int patch_branch(unsigned int *addr, uns
int patch_instruction(unsigned int *addr, unsigned int instr);

int instr_is_relative_branch(unsigned int instr);
+int instr_is_relative_link_branch(unsigned int instr);
int instr_is_branch_to_addr(const unsigned int *instr, unsigned long addr);
unsigned long branch_target(const unsigned int *instr);
unsigned int translate_branch(const unsigned int *dest,
--- a/arch/powerpc/kernel/module_64.c
+++ b/arch/powerpc/kernel/module_64.c
@@ -487,7 +487,17 @@ static bool is_early_mcount_callsite(u32
restore r2. */
static int restore_r2(u32 *instruction, struct module *me)
{
- if (is_early_mcount_callsite(instruction - 1))
+ u32 *prev_insn = instruction - 1;
+
+ if (is_early_mcount_callsite(prev_insn))
+ return 1;
+
+ /*
+ * Make sure the branch isn't a sibling call. Sibling calls aren't
+ * "link" branches and they don't return, so they don't need the r2
+ * restore afterwards.
+ */
+ if (!instr_is_relative_link_branch(*prev_insn))
return 1;

if (*instruction != PPC_INST_NOP) {
--- a/arch/powerpc/lib/code-patching.c
+++ b/arch/powerpc/lib/code-patching.c
@@ -302,6 +302,11 @@ int instr_is_relative_branch(unsigned in
return instr_is_branch_iform(instr) || instr_is_branch_bform(instr);
}

+int instr_is_relative_link_branch(unsigned int instr)
+{
+ return instr_is_relative_branch(instr) && (instr & BRANCH_SET_LINK);
+}
+
static unsigned long branch_iform_target(const unsigned int *instr)
{
signed long imm;