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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 /arch/x86
parent870fd0f5df4e131467612cc46db46fc3b69fd706 (diff)
parentf638f4dc0880d515c807a67b8210885a4a4f18bb (diff)
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 'arch/x86')
-rw-r--r--arch/x86/Kconfig3
-rw-r--r--arch/x86/include/asm/livepatch.h46
-rw-r--r--arch/x86/kernel/Makefile1
-rw-r--r--arch/x86/kernel/livepatch.c90
4 files changed, 140 insertions, 0 deletions
diff --git a/arch/x86/Kconfig b/arch/x86/Kconfig
index 019f4e5c2b75..33ce9a344e38 100644
--- a/arch/x86/Kconfig
+++ b/arch/x86/Kconfig
@@ -17,6 +17,7 @@ config X86_64
depends on 64BIT
select X86_DEV_DMA_OPS
select ARCH_USE_CMPXCHG_LOCKREF
+ select HAVE_LIVEPATCH
### Arch settings
config X86
@@ -2028,6 +2029,8 @@ config CMDLINE_OVERRIDE
This is used to work around broken boot loaders. This should
be set to 'N' under normal conditions.
+source "kernel/livepatch/Kconfig"
+
endmenu
config ARCH_ENABLE_MEMORY_HOTPLUG
diff --git a/arch/x86/include/asm/livepatch.h b/arch/x86/include/asm/livepatch.h
new file mode 100644
index 000000000000..a455a53d789a
--- /dev/null
+++ b/arch/x86/include/asm/livepatch.h
@@ -0,0 +1,46 @@
+/*
+ * livepatch.h - x86-specific Kernel Live Patching Core
+ *
+ * Copyright (C) 2014 Seth Jennings <sjenning@redhat.com>
+ * Copyright (C) 2014 SUSE
+ *
+ * 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/>.
+ */
+
+#ifndef _ASM_X86_LIVEPATCH_H
+#define _ASM_X86_LIVEPATCH_H
+
+#include <linux/module.h>
+#include <linux/ftrace.h>
+
+#ifdef CONFIG_LIVEPATCH
+static inline int klp_check_compiler_support(void)
+{
+#ifndef CC_USING_FENTRY
+ return 1;
+#endif
+ return 0;
+}
+extern int klp_write_module_reloc(struct module *mod, unsigned long type,
+ unsigned long loc, unsigned long value);
+
+static inline void klp_arch_set_pc(struct pt_regs *regs, unsigned long ip)
+{
+ regs->ip = ip;
+}
+#else
+#error Live patching support is disabled; check CONFIG_LIVEPATCH
+#endif
+
+#endif /* _ASM_X86_LIVEPATCH_H */
diff --git a/arch/x86/kernel/Makefile b/arch/x86/kernel/Makefile
index 5d4502c8b983..732223496968 100644
--- a/arch/x86/kernel/Makefile
+++ b/arch/x86/kernel/Makefile
@@ -63,6 +63,7 @@ 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 000000000000..ff3c3101d003
--- /dev/null
+++ b/arch/x86/kernel/livepatch.c
@@ -0,0 +1,90 @@
+/*
+ * livepatch.c - x86-specific Kernel Live Patching Core
+ *
+ * Copyright (C) 2014 Seth Jennings <sjenning@redhat.com>
+ * Copyright (C) 2014 SUSE
+ *
+ * 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/uaccess.h>
+#include <asm/cacheflush.h>
+#include <asm/page_types.h>
+#include <asm/elf.h>
+#include <asm/livepatch.h>
+
+/**
+ * klp_write_module_reloc() - write a relocation in a module
+ * @mod: module in which the section to be modified is found
+ * @type: ELF relocation type (see asm/elf.h)
+ * @loc: address that the relocation should be written to
+ * @value: relocation value (sym address + addend)
+ *
+ * This function writes a relocation to the specified location for
+ * a particular module.
+ */
+int klp_write_module_reloc(struct module *mod, unsigned long type,
+ unsigned long loc, unsigned long value)
+{
+ int ret, numpages, size = 4;
+ bool readonly;
+ unsigned long val;
+ unsigned long core = (unsigned long)mod->module_core;
+ unsigned long core_ro_size = mod->core_ro_size;
+ unsigned long core_size = mod->core_size;
+
+ switch (type) {
+ case R_X86_64_NONE:
+ return 0;
+ case R_X86_64_64:
+ val = value;
+ size = 8;
+ break;
+ case R_X86_64_32:
+ val = (u32)value;
+ break;
+ case R_X86_64_32S:
+ val = (s32)value;
+ break;
+ case R_X86_64_PC32:
+ val = (u32)(value - loc);
+ break;
+ default:
+ /* unsupported relocation type */
+ return -EINVAL;
+ }
+
+ if (loc < core || loc >= core + core_size)
+ /* loc does not point to any symbol inside the module */
+ return -EINVAL;
+
+ if (loc < core + core_ro_size)
+ readonly = true;
+ else
+ readonly = false;
+
+ /* determine if the relocation spans a page boundary */
+ numpages = ((loc & PAGE_MASK) == ((loc + size) & PAGE_MASK)) ? 1 : 2;
+
+ if (readonly)
+ set_memory_rw(loc & PAGE_MASK, numpages);
+
+ ret = probe_kernel_write((void *)loc, &val, size);
+
+ if (readonly)
+ set_memory_ro(loc & PAGE_MASK, numpages);
+
+ return ret;
+}