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authorLinus Torvalds <torvalds@linux-foundation.org>2015-02-10 18:35:40 -0800
committerLinus Torvalds <torvalds@linux-foundation.org>2015-02-10 18:35:40 -0800
commit1d9c5d79e6e4385aea6f69c23ba543717434ed70 (patch)
treed5bbe45e95f85c8a8b5d980b4a619c0ca82a9da6 /samples
parent870fd0f5df4e131467612cc46db46fc3b69fd706 (diff)
parentf638f4dc0880d515c807a67b8210885a4a4f18bb (diff)
downloadkernel-1d9c5d79e6e4385aea6f69c23ba543717434ed70.tar.gz
Merge branch 'for-linus' of git://git.kernel.org/pub/scm/linux/kernel/git/jikos/livepatching
Pull live patching infrastructure from Jiri Kosina: "Let me provide a bit of history first, before describing what is in this pile. Originally, there was kSplice as a standalone project that implemented stop_machine()-based patching for the linux kernel. This project got later acquired, and the current owner is providing live patching as a proprietary service, without any intentions to have their implementation merged. Then, due to rising user/customer demand, both Red Hat and SUSE started working on their own implementation (not knowing about each other), and announced first versions roughly at the same time [1] [2]. The principle difference between the two solutions is how they are making sure that the patching is performed in a consistent way when it comes to different execution threads with respect to the semantic nature of the change that is being introduced. In a nutshell, kPatch is issuing stop_machine(), then looking at stacks of all existing processess, and if it decides that the system is in a state that can be patched safely, it proceeds insterting code redirection machinery to the patched functions. On the other hand, kGraft provides a per-thread consistency during one single pass of a process through the kernel and performs a lazy contignuous migration of threads from "unpatched" universe to the "patched" one at safe checkpoints. If interested in a more detailed discussion about the consistency models and its possible combinations, please see the thread that evolved around [3]. It pretty quickly became obvious to the interested parties that it's absolutely impractical in this case to have several isolated solutions for one task to co-exist in the kernel. During a dedicated Live Kernel Patching track at LPC in Dusseldorf, all the interested parties sat together and came up with a joint aproach that would work for both distro vendors. Steven Rostedt took notes [4] from this meeting. And the foundation for that aproach is what's present in this pull request. It provides a basic infrastructure for function "live patching" (i.e. code redirection), including API for kernel modules containing the actual patches, and API/ABI for userspace to be able to operate on the patches (look up what patches are applied, enable/disable them, etc). It's relatively simple and minimalistic, as it's making use of existing kernel infrastructure (namely ftrace) as much as possible. It's also self-contained, in a sense that it doesn't hook itself in any other kernel subsystem (it doesn't even touch any other code). It's now implemented for x86 only as a reference architecture, but support for powerpc, s390 and arm is already in the works (adding arch-specific support basically boils down to teaching ftrace about regs-saving). Once this common infrastructure gets merged, both Red Hat and SUSE have agreed to immediately start porting their current solutions on top of this, abandoning their out-of-tree code. The plan basically is that each patch will be marked by flag(s) that would indicate which consistency model it is willing to use (again, the details have been sketched out already in the thread at [3]). Before this happens, the current codebase can be used to patch a large group of secruity/stability problems the patches for which are not too complex (in a sense that they don't introduce non-trivial change of function's return value semantics, they don't change layout of data structures, etc) -- this corresponds to LEAVE_FUNCTION && SWITCH_FUNCTION semantics described at [3]. This tree has been in linux-next since December. [1] https://lkml.org/lkml/2014/4/30/477 [2] https://lkml.org/lkml/2014/7/14/857 [3] https://lkml.org/lkml/2014/11/7/354 [4] http://linuxplumbersconf.org/2014/wp-content/uploads/2014/10/LPC2014_LivePatching.txt [ The core code is introduced by the three commits authored by Seth Jennings, which got a lot of changes incorporated during numerous respins and reviews of the initial implementation. All the followup commits have materialized only after public tree has been created, so they were not folded into initial three commits so that the public tree doesn't get rebased ]" * 'for-linus' of git://git.kernel.org/pub/scm/linux/kernel/git/jikos/livepatching: livepatch: add missing newline to error message livepatch: rename config to CONFIG_LIVEPATCH livepatch: fix uninitialized return value livepatch: support for repatching a function livepatch: enforce patch stacking semantics livepatch: change ARCH_HAVE_LIVE_PATCHING to HAVE_LIVE_PATCHING livepatch: fix deferred module patching order livepatch: handle ancient compilers with more grace livepatch: kconfig: use bool instead of boolean livepatch: samples: fix usage example comments livepatch: MAINTAINERS: add git tree location livepatch: use FTRACE_OPS_FL_IPMODIFY livepatch: move x86 specific ftrace handler code to arch/x86 livepatch: samples: add sample live patching module livepatch: kernel: add support for live patching livepatch: kernel: add TAINT_LIVEPATCH
Diffstat (limited to 'samples')
-rw-r--r--samples/Kconfig7
-rw-r--r--samples/Makefile2
-rw-r--r--samples/livepatch/Makefile1
-rw-r--r--samples/livepatch/livepatch-sample.c91
4 files changed, 100 insertions, 1 deletions
diff --git a/samples/Kconfig b/samples/Kconfig
index 6181c2cc9ca0..224ebb46bed5 100644
--- a/samples/Kconfig
+++ b/samples/Kconfig
@@ -63,4 +63,11 @@ config SAMPLE_RPMSG_CLIENT
to communicate with an AMP-configured remote processor over
the rpmsg bus.
+config SAMPLE_LIVEPATCH
+ tristate "Build live patching sample -- loadable modules only"
+ depends on LIVEPATCH && m
+ help
+ Builds a sample live patch that replaces the procfs handler
+ for /proc/cmdline to print "this has been live patched".
+
endif # SAMPLES
diff --git a/samples/Makefile b/samples/Makefile
index 1a60c62e2045..f00257bcc5a7 100644
--- a/samples/Makefile
+++ b/samples/Makefile
@@ -1,4 +1,4 @@
# Makefile for Linux samples code
-obj-$(CONFIG_SAMPLES) += kobject/ kprobes/ trace_events/ \
+obj-$(CONFIG_SAMPLES) += kobject/ kprobes/ trace_events/ livepatch/ \
hw_breakpoint/ kfifo/ kdb/ hidraw/ rpmsg/ seccomp/
diff --git a/samples/livepatch/Makefile b/samples/livepatch/Makefile
new file mode 100644
index 000000000000..10319d7ea0b1
--- /dev/null
+++ b/samples/livepatch/Makefile
@@ -0,0 +1 @@
+obj-$(CONFIG_SAMPLE_LIVEPATCH) += livepatch-sample.o
diff --git a/samples/livepatch/livepatch-sample.c b/samples/livepatch/livepatch-sample.c
new file mode 100644
index 000000000000..fb8c8614e728
--- /dev/null
+++ b/samples/livepatch/livepatch-sample.c
@@ -0,0 +1,91 @@
+/*
+ * livepatch-sample.c - Kernel Live Patching Sample Module
+ *
+ * Copyright (C) 2014 Seth Jennings <sjenning@redhat.com>
+ *
+ * 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/kernel.h>
+#include <linux/livepatch.h>
+
+/*
+ * This (dumb) live patch overrides the function that prints the
+ * kernel boot cmdline when /proc/cmdline is read.
+ *
+ * Example:
+ *
+ * $ cat /proc/cmdline
+ * <your cmdline>
+ *
+ * $ insmod livepatch-sample.ko
+ * $ cat /proc/cmdline
+ * this has been live patched
+ *
+ * $ echo 0 > /sys/kernel/livepatch/livepatch_sample/enabled
+ * $ cat /proc/cmdline
+ * <your cmdline>
+ */
+
+#include <linux/seq_file.h>
+static int livepatch_cmdline_proc_show(struct seq_file *m, void *v)
+{
+ seq_printf(m, "%s\n", "this has been live patched");
+ return 0;
+}
+
+static struct klp_func funcs[] = {
+ {
+ .old_name = "cmdline_proc_show",
+ .new_func = livepatch_cmdline_proc_show,
+ }, { }
+};
+
+static struct klp_object objs[] = {
+ {
+ /* name being NULL means vmlinux */
+ .funcs = funcs,
+ }, { }
+};
+
+static struct klp_patch patch = {
+ .mod = THIS_MODULE,
+ .objs = objs,
+};
+
+static int livepatch_init(void)
+{
+ int ret;
+
+ ret = klp_register_patch(&patch);
+ if (ret)
+ return ret;
+ ret = klp_enable_patch(&patch);
+ if (ret) {
+ WARN_ON(klp_unregister_patch(&patch));
+ return ret;
+ }
+ return 0;
+}
+
+static void livepatch_exit(void)
+{
+ WARN_ON(klp_disable_patch(&patch));
+ WARN_ON(klp_unregister_patch(&patch));
+}
+
+module_init(livepatch_init);
+module_exit(livepatch_exit);
+MODULE_LICENSE("GPL");