[RFC 2/2] arm64: Implement HAVE_LIVEPATCH

[Song Liu]

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

Test coverage:

- Passed manual tests with samples/livepatch.
- Passed all but test-kprobe.sh in selftests/livepatch.
  test-kprobe.sh is expected to fail, because arm64 doesn't have
  KPROBES_ON_FTRACE.
- Passed tests with kpatch-build [2]. (This version includes commits that
  are not merged to upstream kpatch yet).

[1] https://lore.kernel.org/all/20210604235930.603-1-surajjs@xxxxxxxxxx/
[2] https://github.com/liu-song-6/kpatch/tree/fb-6.13
Cc: Suraj Jitindar Singh <surajjs@xxxxxxxxxx>
Cc: Torsten Duwe <duwe@xxxxxxx>
Signed-off-by: Song Liu <song@xxxxxxxxxx>
---
 arch/arm64/Kconfig                   | 3 +++
 arch/arm64/include/asm/thread_info.h | 4 +++-
 arch/arm64/kernel/entry-common.c     | 4 ++++
 3 files changed, 10 insertions(+), 1 deletion(-)

diff --git a/arch/arm64/Kconfig b/arch/arm64/Kconfig
index f5af6faf9e2b..475caa57c94a 100644
--- a/arch/arm64/Kconfig
+++ b/arch/arm64/Kconfig
@@ -272,6 +272,7 @@ config ARM64
 	select USER_STACKTRACE_SUPPORT
 	select VDSO_GETRANDOM
 	select HAVE_RELIABLE_STACKTRACE
+	select HAVE_LIVEPATCH
 	help
 	  ARM 64-bit (AArch64) Linux support.
 
@@ -2496,3 +2497,5 @@ endmenu # "CPU Power Management"
 source "drivers/acpi/Kconfig"
 
 source "arch/arm64/kvm/Kconfig"
+
+source "kernel/livepatch/Kconfig"
diff --git a/arch/arm64/include/asm/thread_info.h b/arch/arm64/include/asm/thread_info.h
index 1114c1c3300a..01623c471beb 100644
--- a/arch/arm64/include/asm/thread_info.h
+++ b/arch/arm64/include/asm/thread_info.h
@@ -69,6 +69,7 @@ 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
@@ -92,6 +93,7 @@ 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)
@@ -103,7 +105,7 @@ void arch_setup_new_exec(void);
 #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/entry-common.c b/arch/arm64/kernel/entry-common.c
index b260ddc4d3e9..b537af333b42 100644
--- a/arch/arm64/kernel/entry-common.c
+++ b/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);
 
-- 
2.43.5