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: Jessica Yu <jeyu@redhat.com>
Acked-by: Miroslav Benes <mbenes@suse.cz>
Signed-off-by: Jiri Kosina <jkosina@suse.cz>

diff --git a/arch/x86/kernel/Makefile b/arch/x86/kernel/Makefile
index 0503f5bfb18d221d35139ecd525f9b1af9e0761f..4f656fe156fd644a395a88715947ab1e75761e94 100644 (file)
--- a/arch/x86/kernel/Makefile
+++ b/arch/x86/kernel/Makefile
@@ -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

diff --git a/arch/x86/kernel/livepatch.c b/arch/x86/kernel/livepatch.c
new file mode 100644 (file)
index 0000000..e9d252d
--- /dev/null
+++ b/arch/x86/kernel/livepatch.c
@@ -0,0 +1,65 @@
+/*
+ * 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);
+       }
+}