[RFC PATCH v2 19/20] arm64: Miscellaneous changes required for enabling livepatch

[madvenka@xxxxxxxxxxxxxxxxxxx]

From: "Madhavan T. Venkataraman" <madvenka@xxxxxxxxxxxxxxxxxxx>

	- Create arch/arm64/include/asm/livepatch.h and define
	  klp_arch_set_pc() and klp_get_ftrace_location() which
	  are required for livepatch.

	- Define TIF_PATCH_PENDING in arch/arm64/include/asm/thread_info.h
	  for livepatch.

	- Check TIF_PATCH_PENDING in do_notify_resume() to patch the
	  current task for livepatch.

Signed-off-by: Suraj Jitindar Singh <sjitindarsingh@xxxxxxxxx>
Signed-off-by: Madhavan T. Venkataraman <madvenka@xxxxxxxxxxxxxxxxxxx>
---
 arch/arm64/include/asm/livepatch.h   | 42 ++++++++++++++++++++++++++++
 arch/arm64/include/asm/thread_info.h |  4 ++-
 arch/arm64/kernel/signal.c           |  4 +++
 3 files changed, 49 insertions(+), 1 deletion(-)
 create mode 100644 arch/arm64/include/asm/livepatch.h

diff --git a/arch/arm64/include/asm/livepatch.h b/arch/arm64/include/asm/livepatch.h
new file mode 100644
index 000000000000..72d7cd86f158
--- /dev/null
+++ b/arch/arm64/include/asm/livepatch.h
@@ -0,0 +1,42 @@
+/* SPDX-License-Identifier: GPL-2.0
+ *
+ * livepatch.h - arm64-specific Kernel Live Patching Core
+ */
+#ifndef _ASM_ARM64_LIVEPATCH_H
+#define _ASM_ARM64_LIVEPATCH_H
+
+#include <linux/ftrace.h>
+
+static inline void klp_arch_set_pc(struct ftrace_regs *fregs, unsigned long ip)
+{
+	struct pt_regs *regs = ftrace_get_regs(fregs);
+
+	regs->pc = ip;
+}
+
+/*
+ * klp_get_ftrace_location is expected to return the address of the BL to the
+ * relevant ftrace handler in the callsite. The location of this can vary based
+ * on several compilation options.
+ * CONFIG_DYNAMIC_FTRACE_WITH_REGS
+ *	- Inserts 2 nops on function entry the second of which is the BL
+ *	  referenced above. (See ftrace_init_nop() for the callsite sequence)
+ *	  (this is required by livepatch and must be selected)
+ * CONFIG_ARM64_BTI_KERNEL:
+ *	- Inserts a hint #0x22 on function entry if the function is called
+ *	  indirectly (to satisfy BTI requirements), which is inserted before
+ *	  the two nops from above.
+ */
+#define klp_get_ftrace_location klp_get_ftrace_location
+static inline unsigned long klp_get_ftrace_location(unsigned long faddr)
+{
+	unsigned long addr = faddr + AARCH64_INSN_SIZE;
+
+#if IS_ENABLED(CONFIG_ARM64_BTI_KERNEL)
+	addr = ftrace_location_range(addr, addr + AARCH64_INSN_SIZE);
+#endif
+
+	return addr;
+}
+
+#endif /* _ASM_ARM64_LIVEPATCH_H */
diff --git a/arch/arm64/include/asm/thread_info.h b/arch/arm64/include/asm/thread_info.h
index e1317b7c4525..a1d8999dbdcc 100644
--- a/arch/arm64/include/asm/thread_info.h
+++ b/arch/arm64/include/asm/thread_info.h
@@ -68,6 +68,7 @@ int arch_dup_task_struct(struct task_struct *dst,
 #define TIF_UPROBE		4	/* uprobe breakpoint or singlestep */
 #define TIF_MTE_ASYNC_FAULT	5	/* MTE Asynchronous Tag Check Fault */
 #define TIF_NOTIFY_SIGNAL	6	/* signal notifications exist */
+#define TIF_PATCH_PENDING	7	/* pending live patching update */
 #define TIF_SYSCALL_TRACE	8	/* syscall trace active */
 #define TIF_SYSCALL_AUDIT	9	/* syscall auditing */
 #define TIF_SYSCALL_TRACEPOINT	10	/* syscall tracepoint for ftrace */
@@ -98,11 +99,12 @@ int arch_dup_task_struct(struct task_struct *dst,
 #define _TIF_SVE		(1 << TIF_SVE)
 #define _TIF_MTE_ASYNC_FAULT	(1 << TIF_MTE_ASYNC_FAULT)
 #define _TIF_NOTIFY_SIGNAL	(1 << TIF_NOTIFY_SIGNAL)
+#define _TIF_PATCH_PENDING	(1 << TIF_PATCH_PENDING)
 
 #define _TIF_WORK_MASK		(_TIF_NEED_RESCHED | _TIF_SIGPENDING | \
 				 _TIF_NOTIFY_RESUME | _TIF_FOREIGN_FPSTATE | \
 				 _TIF_UPROBE | _TIF_MTE_ASYNC_FAULT | \
-				 _TIF_NOTIFY_SIGNAL)
+				 _TIF_NOTIFY_SIGNAL | _TIF_PATCH_PENDING)
 
 #define _TIF_SYSCALL_WORK	(_TIF_SYSCALL_TRACE | _TIF_SYSCALL_AUDIT | \
 				 _TIF_SYSCALL_TRACEPOINT | _TIF_SECCOMP | \
diff --git a/arch/arm64/kernel/signal.c b/arch/arm64/kernel/signal.c
index 4a4122ef6f39..cbec9597349f 100644
--- a/arch/arm64/kernel/signal.c
+++ b/arch/arm64/kernel/signal.c
@@ -17,6 +17,7 @@
 #include <linux/sizes.h>
 #include <linux/string.h>
 #include <linux/resume_user_mode.h>
+#include <linux/livepatch.h>
 #include <linux/ratelimit.h>
 #include <linux/syscalls.h>
 
@@ -938,6 +939,9 @@ void do_notify_resume(struct pt_regs *regs, unsigned long thread_flags)
 					       (void __user *)NULL, current);
 			}
 
+			if (thread_flags & _TIF_PATCH_PENDING)
+				klp_update_patch_state(current);
+
 			if (thread_flags & (_TIF_SIGPENDING | _TIF_NOTIFY_SIGNAL))
 				do_signal(regs);
 
-- 
2.25.1