arm64: fix function types in COND_SYSCALL

Define a weak function in COND_SYSCALL instead of a weak alias to
sys_ni_syscall, which has an incompatible type. This fixes indirect
call mismatches with Control-Flow Integrity (CFI) checking.
Acked-by: NMark Rutland <mark.rutland@arm.com>
Signed-off-by: NSami Tolvanen <samitolvanen@google.com>
Signed-off-by: NWill Deacon <will@kernel.org>

arch/arm64/include/asm/syscall_wrapper.h

@@ -8,6 +8,8 @@
 #ifndef __ASM_SYSCALL_WRAPPER_H
 #define __ASM_SYSCALL_WRAPPER_H
 
+struct pt_regs;
+
 #define SC_ARM64_REGS_TO_ARGS(x, ...)				\
 	__MAP(x,__SC_ARGS					\
 	      ,,regs->regs[0],,regs->regs[1],,regs->regs[2]	\
@@ -35,8 +37,11 @@
 	ALLOW_ERROR_INJECTION(__arm64_compat_sys_##sname, ERRNO);			\
 	asmlinkage long __arm64_compat_sys_##sname(const struct pt_regs *__unused)
 
-#define COND_SYSCALL_COMPAT(name) \
-	cond_syscall(__arm64_compat_sys_##name);
+#define COND_SYSCALL_COMPAT(name) 							\
+	asmlinkage long __weak __arm64_compat_sys_##name(const struct pt_regs *regs)	\
+	{										\
+		return sys_ni_syscall();						\
+	}
 
 #define COMPAT_SYS_NI(name) \
 	SYSCALL_ALIAS(__arm64_compat_sys_##name, sys_ni_posix_timers);
@@ -70,7 +75,11 @@
 #endif
 
 #ifndef COND_SYSCALL
-#define COND_SYSCALL(name) cond_syscall(__arm64_sys_##name)
+#define COND_SYSCALL(name)							\
+	asmlinkage long __weak __arm64_sys_##name(const struct pt_regs *regs)	\
+	{									\
+		return sys_ni_syscall();					\
+	}
 #endif
 
 #ifndef SYS_NI