arm64: Implement HAVE_LIVEPATCH

Allocate a task flag used to represent the patch pending state for the
task. When a livepatch is being loaded or unloaded, the livepatch code
uses this flag to select the proper version of a being patched kernel
functions to use for current task.

In arch/arm64/Kconfig, select HAVE_LIVEPATCH and include proper Kconfig.

This is largely based on [1] by Suraj Jitindar Singh.

[1] https://lore.kernel.org/all/20210604235930.603-1-surajjs@amazon.com/

Cc: Suraj Jitindar Singh <surajjs@amazon.com>
Cc: Torsten Duwe <duwe@suse.de>
Acked-by: Miroslav Benes <mbenes@suse.cz>
Tested-by: Breno Leitao <leitao@debian.org>
Tested-by: Andrea della Porta <andrea.porta@suse.com>
Signed-off-by: Song Liu <song@kernel.org>
Acked-by: Will Deacon <will@kernel.org>
Link: https://lore.kernel.org/r/20250630174502.842486-1-song@kernel.org
Signed-off-by: Catalin Marinas <catalin.marinas@arm.com>

Author: liu-song-6

arch/arm64/Kconfig

@@ -280,6 +280,7 @@ config ARM64
 	select USER_STACKTRACE_SUPPORT
 	select VDSO_GETRANDOM
 	select HAVE_RELIABLE_STACKTRACE
+	select HAVE_LIVEPATCH
 	help
 	  ARM 64-bit (AArch64) Linux support.
 
@@ -2499,3 +2500,5 @@ endmenu # "CPU Power Management"
 source "drivers/acpi/Kconfig"
 
 source "arch/arm64/kvm/Kconfig"
+
+source "kernel/livepatch/Kconfig"

arch/arm64/include/asm/thread_info.h

@@ -70,6 +70,7 @@ void arch_setup_new_exec(void);
 #define TIF_SYSCALL_TRACEPOINT	10	/* syscall tracepoint for ftrace */
 #define TIF_SECCOMP		11	/* syscall secure computing */
 #define TIF_SYSCALL_EMU		12	/* syscall emulation active */
+#define TIF_PATCH_PENDING	13	/* pending live patching update */
 #define TIF_MEMDIE		18	/* is terminating due to OOM killer */
 #define TIF_FREEZE		19
 #define TIF_RESTORE_SIGMASK	20
@@ -96,6 +97,7 @@ void arch_setup_new_exec(void);
 #define _TIF_SYSCALL_TRACEPOINT	(1 << TIF_SYSCALL_TRACEPOINT)
 #define _TIF_SECCOMP		(1 << TIF_SECCOMP)
 #define _TIF_SYSCALL_EMU	(1 << TIF_SYSCALL_EMU)
+#define _TIF_PATCH_PENDING	(1 << TIF_PATCH_PENDING)
 #define _TIF_UPROBE		(1 << TIF_UPROBE)
 #define _TIF_SINGLESTEP		(1 << TIF_SINGLESTEP)
 #define _TIF_32BIT		(1 << TIF_32BIT)
@@ -107,7 +109,8 @@ void arch_setup_new_exec(void);
 #define _TIF_WORK_MASK		(_TIF_NEED_RESCHED | _TIF_NEED_RESCHED_LAZY | \
 				 _TIF_NOTIFY_RESUME | _TIF_FOREIGN_FPSTATE | \
 				 _TIF_UPROBE | _TIF_MTE_ASYNC_FAULT | \
-				 _TIF_NOTIFY_SIGNAL | _TIF_SIGPENDING)
+				 _TIF_NOTIFY_SIGNAL | _TIF_SIGPENDING | \
+				 _TIF_PATCH_PENDING)
 
 #define _TIF_SYSCALL_WORK	(_TIF_SYSCALL_TRACE | _TIF_SYSCALL_AUDIT | \
 				 _TIF_SYSCALL_TRACEPOINT | _TIF_SECCOMP | \

arch/arm64/kernel/entry-common.c

@@ -8,6 +8,7 @@
 #include <linux/context_tracking.h>
 #include <linux/kasan.h>
 #include <linux/linkage.h>
+#include <linux/livepatch.h>
 #include <linux/lockdep.h>
 #include <linux/ptrace.h>
 #include <linux/resume_user_mode.h>
@@ -144,6 +145,9 @@ static 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);