This is a note to let you know that I've just added the patch titled
powerpc/modules: Don't try to restore r2 after a sibling call
to the 4.9-stable tree which can be found at:
http://www.kernel.org/git/?p=linux/kernel/git/stable/stable-queue.git;a=summary
The filename of the patch is:
powerpc-modules-don-t-try-to-restore-r2-after-a-sibling-call.patch
and it can be found in the queue-4.9 subdirectory.
If you, or anyone else, feels it should not be added to the stable tree,
please let <stable@xxxxxxxxxxxxxxx> know about it.
>From foo@baz Sun Mar 18 16:55:33 CET 2018
From: Josh Poimboeuf <jpoimboe@xxxxxxxxxx>
Date: Thu, 16 Nov 2017 11:45:37 -0600
Subject: powerpc/modules: Don't try to restore r2 after a sibling call
From: Josh Poimboeuf <jpoimboe@xxxxxxxxxx>
[ 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@xxxxxxxxxx>
Acked-by: Naveen N. Rao <naveen.n.rao@xxxxxxxxxxxxxxxxxx>
Reviewed-and-tested-by: Kamalesh Babulal <kamalesh@xxxxxxxxxxxxxxxxxx>
Signed-off-by: Michael Ellerman <mpe@xxxxxxxxxxxxxx>
Signed-off-by: Sasha Levin <alexander.levin@xxxxxxxxxxxxx>
Signed-off-by: Greg Kroah-Hartman <gregkh@xxxxxxxxxxxxxxxxxxx>
---
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
@@ -30,6 +30,7 @@ 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
@@ -494,7 +494,17 @@ 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
@@ -95,6 +95,11 @@ 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;
Patches currently in stable-queue which might be from jpoimboe@xxxxxxxxxx are
queue-4.9/powerpc-modules-don-t-try-to-restore-r2-after-a-sibling-call.patch
queue-4.9/kprobes-x86-set-kprobes-pages-read-only.patch
queue-4.9/kprobes-x86-fix-kprobe-booster-not-to-boost-far-call-instructions.patch
queue-4.9/x86-boot-32-defer-resyncing-initial_page_table-until-per-cpu-is-set-up.patch