livepatch: Remove .klp.arch

After the previous patch, vmlinux-specific KLP relocations are now
applied early during KLP module load.  This means that .klp.arch
sections are no longer needed for *vmlinux-specific* KLP relocations.

One might think they're still needed for *module-specific* KLP
relocations.  If a to-be-patched module is loaded *after* its
corresponding KLP module is loaded, any corresponding KLP relocations
will be delayed until the to-be-patched module is loaded.  If any
special sections (.parainstructions, for example) rely on those
relocations, their initializations (apply_paravirt) need to be done
afterwards.  Thus the apparent need for arch_klp_init_object_loaded()
and its corresponding .klp.arch sections -- it allows some of the
special section initializations to be done at a later time.

But... if you look closer, that dependency between the special sections
and the module-specific KLP relocations doesn't actually exist in
reality.  Looking at the contents of the .altinstructions and
.parainstructions sections, there's not a realistic scenario in which a
KLP module's .altinstructions or .parainstructions section needs to
access a symbol in a to-be-patched module.  It might need to access a
local symbol or even a vmlinux symbol; but not another module's symbol.
When a special section needs to reference a local or vmlinux symbol, a
normal rela can be used instead of a KLP rela.

Since the special section initializations don't actually have any real
dependency on module-specific KLP relocations, .klp.arch and
arch_klp_init_object_loaded() no longer have a reason to exist.  So
remove them.

As Peter said much more succinctly:

  So the reason for .klp.arch was that .klp.rela.* stuff would overwrite
  paravirt instructions. If that happens you're doing it wrong. Those
  RELAs are core kernel, not module, and thus should've happened in
  .rela.* sections at patch-module loading time.

  Reverting this removes the two apply_{paravirt,alternatives}() calls
  from the late patching path, and means we don't have to worry about
  them when removing module_disable_ro().

[ jpoimboe: Rewrote patch description.  Tweaked klp_init_object_loaded()
	    error path. ]

Signed-off-by: Peter Zijlstra (Intel) <peterz@infradead.org>
Signed-off-by: Josh Poimboeuf <jpoimboe@redhat.com>
Acked-by: Peter Zijlstra (Intel) <peterz@infradead.org>
Acked-by: Joe Lawrence <joe.lawrence@redhat.com>
Acked-by: Miroslav Benes <mbenes@suse.cz>
Signed-off-by: Jiri Kosina <jkosina@suse.cz>

1 files changed, 0 insertions, 53 deletions

diff --git a/arch/x86/kernel/livepatch.c b/arch/x86/kernel/livepatch.c
deleted file mode 100644
index 6a68e41206e7..000000000000
--- a/arch/x86/kernel/livepatch.c
+++ /dev/null
@@ -1,53 +0,0 @@
-// SPDX-License-Identifier: GPL-2.0-or-later
-/*
- * livepatch.c - x86-specific Kernel Live Patching Core
- */
-
-#include <linux/module.h>
-#include <linux/kallsyms.h>
-#include <linux/livepatch.h>
-#include <asm/text-patching.h>
-
-/* Apply per-object alternatives. Based on x86 module_finalize() */
-void arch_klp_init_object_loaded(struct klp_patch *patch,
-				 struct klp_object *obj)
-{
-	int cnt;
-	struct klp_modinfo *info;
-	Elf_Shdr *s, *alt = NULL, *para = NULL;
-	void *aseg, *pseg;
-	const char *objname;
-	char sec_objname[MODULE_NAME_LEN];
-	char secname[KSYM_NAME_LEN];
-
-	info = patch->mod->klp_info;
-	objname = obj->name ? obj->name : "vmlinux";
-
-	/* See livepatch core code for BUILD_BUG_ON() explanation */
-	BUILD_BUG_ON(MODULE_NAME_LEN < 56 || KSYM_NAME_LEN != 128);
-
-	for (s = info->sechdrs; s < info->sechdrs + info->hdr.e_shnum; s++) {
-		/* Apply per-object .klp.arch sections */
-		cnt = sscanf(info->secstrings + s->sh_name,
-			     ".klp.arch.%55[^.].%127s",
-			     sec_objname, secname);
-		if (cnt != 2)
-			continue;
-		if (strcmp(sec_objname, objname))
-			continue;
-		if (!strcmp(".altinstructions", secname))
-			alt = s;
-		if (!strcmp(".parainstructions", secname))
-			para = s;
-	}
-
-	if (alt) {
-		aseg = (void *) alt->sh_addr;
-		apply_alternatives(aseg, aseg + alt->sh_size);
-	}
-
-	if (para) {
-		pseg = (void *) para->sh_addr;
-		apply_paravirt(pseg, pseg + para->sh_size);
-	}
-}