Commit d4c3e6e1 authored by Jessica Yu's avatar Jessica Yu Committed by Jiri Kosina
Browse files

livepatch/x86: apply alternatives and paravirt patches after relocations 



Implement arch_klp_init_object_loaded() for x86, which applies
alternatives/paravirt patches. This fixes the order in which relocations
and alternatives/paravirt patches are applied.

Previously, if a patch module had alternatives or paravirt patches,
these were applied first by the module loader before livepatch can apply
per-object relocations. The (buggy) sequence of events was:

(1) Load patch module
(2) Apply alternatives and paravirt patches to patch module
    * Note that these are applied to the new functions in the patch module
(3) Apply per-object relocations to patch module when target module loads.
    * This clobbers what was written in step 2

This lead to crashes and corruption in general, since livepatch would
overwrite or step on previously applied alternative/paravirt patches.
The correct sequence of events should be:

(1) Load patch module
(2) Apply per-object relocations to patch module
(3) Apply alternatives and paravirt patches to patch module

This is fixed by delaying paravirt/alternatives patching until after
relocations are applied. Any .altinstructions or .parainstructions
sections are prefixed with ".klp.arch.${objname}" and applied in
arch_klp_init_object_loaded().

Signed-off-by: default avatarJessica Yu <jeyu@redhat.com>
Acked-by: default avatarMiroslav Benes <mbenes@suse.cz>
Signed-off-by: default avatarJiri Kosina <jkosina@suse.cz>
parent 255e732c

arch/x86/kernel/Makefile

+1 −0
Original line number Diff line number Diff line
@@ -83,6 +83,7 @@ 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_GRAPH_TRACER) += ftrace.o

obj-$(CONFIG_FTRACE_SYSCALLS)	+= ftrace.o

obj-$(CONFIG_X86_TSC)		+= trace_clock.o

arch/x86/kernel/livepatch.c

0 → 100644
+65 −0
Original line number Diff line number Diff line 
/*

 * livepatch.c - x86-specific Kernel Live Patching Core

 *

 * This program is free software; you can redistribute it and/or

 * modify it under the terms of the GNU General Public License

 * as published by the Free Software Foundation; either version 2

 * of the License, or (at your option) any later version.

 *

 * This program is distributed in the hope that it will be useful,

 * but WITHOUT ANY WARRANTY; without even the implied warranty of

 * MERCHANTABILITY or FITNESS FOR A PARTICULAR PURPOSE.  See the

 * GNU General Public License for more details.

 *

 * You should have received a copy of the GNU General Public License

 * along with this program; if not, see <http://www.gnu.org/licenses/>.

 */



#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);

	}

}

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