[PATCH 2/3] arm64: implement live patching

Torsten Duwe
2018-08-10T16:03:00Z

Based on ftrace with regs, do the usual thing. Also allocate a
task flag for whatever consistency handling is implemented.
Watch out for interactions with the graph tracer.
This code has been compile-tested, but has not yet seen any
heavy livepatching.

Signed-off-by: Torsten Duwe <duwe@suse.de>

diff --git a/arch/arm64/Kconfig b/arch/arm64/Kconfig
index 28c8c03..31df287 100644
--- a/arch/arm64/Kconfig
+++ b/arch/arm64/Kconfig
@@ -117,6 +117,7 @@ config ARM64
select HAVE_GENERIC_DMA_COHERENT
select HAVE_HW_BREAKPOINT if PERF_EVENTS
select HAVE_IRQ_TIME_ACCOUNTING
+ select HAVE_LIVEPATCH
select HAVE_MEMBLOCK
select HAVE_MEMBLOCK_NODE_MAP if NUMA
select HAVE_NMI
@@ -1343,4 +1344,6 @@ if CRYPTO
source "arch/arm64/crypto/Kconfig"
endif

+source "kernel/livepatch/Kconfig"
+
source "lib/Kconfig"
--- a/arch/arm64/include/asm/thread_info.h
+++ b/arch/arm64/include/asm/thread_info.h
@@ -76,6 +76,7 @@ void arch_release_task_struct(struct tas
#define TIF_FOREIGN_FPSTATE 3 /* CPU's FP state is not current's */
#define TIF_UPROBE 4 /* uprobe breakpoint or singlestep */
#define TIF_FSCHECK 5 /* Check FS is USER_DS on return */
+#define TIF_PATCH_PENDING 6
#define TIF_NOHZ 7
#define TIF_SYSCALL_TRACE 8
#define TIF_SYSCALL_AUDIT 9
@@ -94,6 +95,7 @@ void arch_release_task_struct(struct tas
#define _TIF_NEED_RESCHED (1 << TIF_NEED_RESCHED)
#define _TIF_NOTIFY_RESUME (1 << TIF_NOTIFY_RESUME)
#define _TIF_FOREIGN_FPSTATE (1 << TIF_FOREIGN_FPSTATE)
+#define _TIF_PATCH_PENDING (1 << TIF_PATCH_PENDING)
#define _TIF_NOHZ (1 << TIF_NOHZ)
#define _TIF_SYSCALL_TRACE (1 << TIF_SYSCALL_TRACE)
#define _TIF_SYSCALL_AUDIT (1 << TIF_SYSCALL_AUDIT)
@@ -106,7 +108,8 @@ void arch_release_task_struct(struct tas

#define _TIF_WORK_MASK (_TIF_NEED_RESCHED | _TIF_SIGPENDING | \
_TIF_NOTIFY_RESUME | _TIF_FOREIGN_FPSTATE | \
- _TIF_UPROBE | _TIF_FSCHECK)
+ _TIF_UPROBE | _TIF_FSCHECK | \
+ _TIF_PATCH_PENDING)

#define _TIF_SYSCALL_WORK (_TIF_SYSCALL_TRACE | _TIF_SYSCALL_AUDIT | \
_TIF_SYSCALL_TRACEPOINT | _TIF_SECCOMP | \
diff --git a/arch/arm64/include/asm/livepatch.h b/arch/arm64/include/asm/livepatch.h
new file mode 100644
index 0000000..6b9a3d1
--- /dev/null
+++ b/arch/arm64/include/asm/livepatch.h
@@ -0,0 +1,38 @@
+/* SPDX-License-Identifier: GPL-2.0
+ *
+ * livepatch.h - arm64-specific Kernel Live Patching Core
+ *
+ * Copyright (C) 2016 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_ARM64_LIVEPATCH_H
+#define _ASM_ARM64_LIVEPATCH_H
+
+#include <linux/module.h>
+#include <linux/ftrace.h>
+
+#ifdef CONFIG_LIVEPATCH
+static inline int klp_check_compiler_support(void)
+{
+ return 0;
+}
+
+static inline void klp_arch_set_pc(struct pt_regs *regs, unsigned long ip)
+{
+ regs->pc = ip;
+}
+#endif /* CONFIG_LIVEPATCH */
+
+#endif /* _ASM_ARM64_LIVEPATCH_H */
diff --git a/arch/arm64/kernel/entry-ftrace.S b/arch/arm64/kernel/entry-ftrace.S
index cdb5866..cf640e8 100644
--- a/arch/arm64/kernel/entry-ftrace.S
+++ b/arch/arm64/kernel/entry-ftrace.S
@@ -195,6 +195,9 @@ ENTRY(ftrace_caller)
str x9, [sp, #S_LR]
/* The program counter just after the ftrace call site */
str lr, [sp, #S_PC]
+#if defined(CONFIG_LIVEPATCH) && defined(CONFIG_FUNCTION_GRAPH_TRACER)
+ mov x19,lr /* remember old return address */
+#endif
/* The stack pointer as it was on ftrace_caller entry... */
add x29, sp, #S_FRAME_SIZE+16 /* ...is also our new FP */
str x29, [sp, #S_SP]
@@ -210,6 +213,16 @@ ftrace_call:

bl ftrace_stub

+#if defined(CONFIG_LIVEPATCH) && defined(CONFIG_FUNCTION_GRAPH_TRACER)
+ /* Is the trace function a live patcher an has messed with
+ * the return address?
+ */
+ ldr x9, [sp, #S_PC]
+ cmp x9, x19 /* compare with the value we remembered */
+ /* to not call graph tracer's "call" mechanism twice! */
+ b.ne ftrace_regs_return
+#endif
+
#ifdef CONFIG_FUNCTION_GRAPH_TRACER
.global ftrace_graph_call
ftrace_graph_call: // ftrace_graph_caller();