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Message-Id: <1469078640-26798-3-git-send-email-jeyu@redhat.com>
Date: Thu, 21 Jul 2016 01:24:00 -0400
From: Jessica Yu <jeyu@...hat.com>
To: Josh Poimboeuf <jpoimboe@...hat.com>,
Miroslav Benes <mbenes@...e.cz>,
Petr Mladek <pmladek@...e.com>, Jiri Kosina <jikos@...nel.org>,
Chris J Arges <chris.j.arges@...onical.com>,
Eugene Shatokhin <eugene.shatokhin@...alab.ru>
Cc: live-patching@...r.kernel.org, x86@...nel.org,
linux-kernel@...r.kernel.org, Jessica Yu <jeyu@...hat.com>
Subject: [PATCH v2 2/2] 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 in
a patch module are prefixed with ".klp.arch.${objname}" and applied in
arch_klp_init_object_loaded().
Signed-off-by: Jessica Yu <jeyu@...hat.com>
---
arch/x86/kernel/Makefile | 1 +
arch/x86/kernel/livepatch.c | 65 +++++++++++++++++++++++++++++++++++++++++++++
2 files changed, 66 insertions(+)
create mode 100644 arch/x86/kernel/livepatch.c
diff --git a/arch/x86/kernel/Makefile b/arch/x86/kernel/Makefile
index 0503f5b..4f656fe 100644
--- a/arch/x86/kernel/Makefile
+++ b/arch/x86/kernel/Makefile
@@ -83,6 +83,7 @@ obj-$(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
index 0000000..78209f1
--- /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);
+ }
+}
--
2.5.5
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