[PATCH stable 4.9] powerpc/lib: fix book3s/32 boot failure due to code patching

[Christophe Leroy]

[Backport of upstream commit b45ba4a51cde29b2939365ef0c07ad34c8321789]

On powerpc32, patch_instruction() is called by apply_feature_fixups()
which is called from early_init()

There is the following note in front of early_init():
 * Note that the kernel may be running at an address which is different
 * from the address that it was linked at, so we must use RELOC/PTRRELOC
 * to access static data (including strings).  -- paulus

Therefore init_mem_is_free must be accessed with PTRRELOC()

Fixes: 1c38a84d4586 ("powerpc: Avoid code patching freed init sections")
Link: https://bugzilla.kernel.org/show_bug.cgi?id=203597
Signed-off-by: Christophe Leroy <christophe.leroy at c-s.fr>

---
Can't apply the upstream commit as such due to several other unrelated stuff
like for instance STRICT_KERNEL_RWX which are missing.
So instead, using same approach as for commit 252eb55816a6f69ef9464cad303cdb3326cdc61d
---
 arch/powerpc/lib/code-patching.c | 2 +-
 1 file changed, 1 insertion(+), 1 deletion(-)

diff --git a/arch/powerpc/lib/code-patching.c b/arch/powerpc/lib/code-patching.c
index 14535ad4cdd1..c312955977ce 100644
--- a/arch/powerpc/lib/code-patching.c
+++ b/arch/powerpc/lib/code-patching.c
@@ -23,7 +23,7 @@ int patch_instruction(unsigned int *addr, unsigned int instr)
 	int err;
 
 	/* Make sure we aren't patching a freed init section */
-	if (init_mem_is_free && init_section_contains(addr, 4)) {
+	if (*PTRRELOC(&init_mem_is_free) && init_section_contains(addr, 4)) {
 		pr_debug("Skipping init section patching addr: 0x%px\n", addr);
 		return 0;
 	}
-- 
2.13.3