powerpc/feature-fixups: Do not patch init section after init

Once init section is freed, attempting to patch init code
ends up in the weed.

Commit 51c3c62b ("powerpc: Avoid code patching freed init sections")
protected patch_instruction() against that, but it is the responsibility
of the caller to ensure that the patched memory is valid.

In the same spirit as jump_label with its jump_label_can_update()
function, add is_fixup_addr_valid() function to skip patching on
freed init section.
Signed-off-by: Christophe Leroy <christophe.leroy@csgroup.eu>
Signed-off-by: Michael Ellerman <mpe@ellerman.id.au>
Link: https://lore.kernel.org/r/8e9311fc1b057e4e6a2a3a0701ebcc74b787affe.1669969781.git.christophe.leroy@csgroup.eu

arch/powerpc/lib/feature-fixups.c

@@ -118,6 +118,12 @@ void do_feature_fixups(unsigned long value, void *fixup_start, void *fixup_end)
 }
 
 #ifdef CONFIG_PPC_BARRIER_NOSPEC
+static bool is_fixup_addr_valid(void *dest, size_t size)
+{
+	return system_state < SYSTEM_FREEING_INITMEM ||
+	       !init_section_contains(dest, size);
+}
+
 static int do_patch_fixups(long *start, long *end, unsigned int *instrs, int num)
 {
 	int i;
@@ -126,6 +132,9 @@ static int do_patch_fixups(long *start, long *end, unsigned int *instrs, int num
 		int j;
 		unsigned int *dest = (void *)start + *start;
 
+		if (!is_fixup_addr_valid(dest, sizeof(*instrs) * num))
+			continue;
+
 		pr_devel("patching dest %lx\n", (unsigned long)dest);
 
 		for (j = 0; j < num; j++)
@@ -144,6 +153,9 @@ static int do_patch_entry_fixups(long *start, long *end, unsigned int *instrs,
 	for (i = 0; start < end; start++, i++) {
 		unsigned int *dest = (void *)start + *start;
 
+		if (!is_fixup_addr_valid(dest, sizeof(*instrs) * 3))
+			continue;
+
 		pr_devel("patching dest %lx\n", (unsigned long)dest);
 
 		// See comment in do_entry_flush_fixups() RE order of patching