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>

diff --git a/Documentation/livepatch/module-elf-format.rst b/Documentation/livepatch/module-elf-format.rst
index 2a591e6..8c6b894 100644 (file)
--- a/Documentation/livepatch/module-elf-format.rst
+++ b/Documentation/livepatch/module-elf-format.rst
@@ -14,8 +14,7 @@ This document outlines the Elf format requirements that livepatch modules must f
    4. Livepatch symbols
       4.1 A livepatch module's symbol table
       4.2 Livepatch symbol format
-   5. Architecture-specific sections
-   6. Symbol table and Elf section access
+   5. Symbol table and Elf section access
 
 1. Background and motivation
 ============================
@@ -298,17 +297,7 @@ Examples:
   Note that the 'Ndx' (Section index) for these symbols is SHN_LIVEPATCH (0xff20).
   "OS" means OS-specific.
 
-5. Architecture-specific sections
-=================================
-Architectures may override arch_klp_init_object_loaded() to perform
-additional arch-specific tasks when a target module loads, such as applying
-arch-specific sections. On x86 for example, we must apply per-object
-.altinstructions and .parainstructions sections when a target module loads.
-These sections must be prefixed with ".klp.arch.$objname." so that they can
-be easily identified when iterating through a patch module's Elf sections
-(See arch/x86/kernel/livepatch.c for a complete example).
-
-6. Symbol table and Elf section access
+5. Symbol table and Elf section access
 ======================================
 A livepatch module's symbol table is accessible through module->symtab.
 

diff --git a/arch/x86/kernel/Makefile b/arch/x86/kernel/Makefile
index ba89cab..bae9f90 100644 (file)
--- a/arch/x86/kernel/Makefile
+++ b/arch/x86/kernel/Makefile
@@ -90,7 +90,6 @@ obj-$(CONFIG_X86_MPPARSE)     += mpparse.o
 obj-y                          += apic/
 obj-$(CONFIG_X86_REBOOTFIXUPS) += reboot_fixups_32.o
 obj-$(CONFIG_DYNAMIC_FTRACE)   += ftrace.o
-obj-$(CONFIG_LIVEPATCH)        += livepatch.o
 obj-$(CONFIG_FUNCTION_TRACER)  += ftrace_$(BITS).o
 obj-$(CONFIG_FUNCTION_GRAPH_TRACER) += ftrace.o
 obj-$(CONFIG_FTRACE_SYSCALLS)  += ftrace.o

diff --git a/arch/x86/kernel/livepatch.c b/arch/x86/kernel/livepatch.c
deleted file mode 100644 (file)
index 6a68e41..0000000
--- 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);
-       }
-}

diff --git a/include/linux/livepatch.h b/include/linux/livepatch.h
index c4302e9..2614247 100644 (file)
--- a/include/linux/livepatch.h
+++ b/include/linux/livepatch.h
@@ -195,9 +195,6 @@ struct klp_patch {
 
 int klp_enable_patch(struct klp_patch *);
 
-void arch_klp_init_object_loaded(struct klp_patch *patch,
-                                struct klp_object *obj);
-
 /* Called from the module loader during module coming/going states */
 int klp_module_coming(struct module *mod);
 void klp_module_going(struct module *mod);

diff --git a/kernel/livepatch/core.c b/kernel/livepatch/core.c
index c02791e..16632e7 100644 (file)
--- a/kernel/livepatch/core.c
+++ b/kernel/livepatch/core.c
@@ -729,12 +729,6 @@ static int klp_init_func(struct klp_object *obj, struct klp_func *func)
                           func->old_sympos ? func->old_sympos : 1);
 }
 
-/* Arches may override this to finish any remaining arch-specific tasks */
-void __weak arch_klp_init_object_loaded(struct klp_patch *patch,
-                                       struct klp_object *obj)
-{
-}
-
 int klp_apply_object_relocs(struct klp_patch *patch, struct klp_object *obj)
 {
        int i, ret;
@@ -764,10 +758,11 @@ static int klp_init_object_loaded(struct klp_patch *patch,
        struct klp_func *func;
        int ret;
 
-       mutex_lock(&text_mutex);
-       module_disable_ro(patch->mod);
-
        if (klp_is_module(obj)) {
+
+               mutex_lock(&text_mutex);
+               module_disable_ro(patch->mod);
+
                /*
                 * Only write module-specific relocations here
                 * (.klp.rela.{module}.*).  vmlinux-specific relocations were
@@ -775,17 +770,13 @@ static int klp_init_object_loaded(struct klp_patch *patch,
                 * itself.
                 */
                ret = klp_apply_object_relocs(patch, obj);
-               if (ret) {
-                       module_enable_ro(patch->mod, true);
-                       mutex_unlock(&text_mutex);
-                       return ret;
-               }
-       }
 
-       arch_klp_init_object_loaded(patch, obj);
+               module_enable_ro(patch->mod, true);
+               mutex_unlock(&text_mutex);
 
-       module_enable_ro(patch->mod, true);
-       mutex_unlock(&text_mutex);
+               if (ret)
+                       return ret;
+       }
 
        klp_for_each_func(obj, func) {
                ret = klp_find_object_symbol(obj->name, func->old_name,