objtool: Add CONFIG_HAVE_UACCESS_VALIDATION

Allow an arch specify that it has objtool uaccess validation with
CONFIG_HAVE_UACCESS_VALIDATION.  For now, doing so unconditionally
selects CONFIG_OBJTOOL.
Signed-off-by: Josh Poimboeuf <jpoimboe@redhat.com>
Signed-off-by: Peter Zijlstra (Intel) <peterz@infradead.org>
Link: https://lkml.kernel.org/r/d393d5e2fe73aec6e8e41d5c24f4b6fe8583f2d8.1650384225.git.jpoimboe@redhat.com

arch/Kconfig

@@ -1050,6 +1050,10 @@ config HAVE_NOINSTR_HACK
 config HAVE_NOINSTR_VALIDATION
 	bool
 
+config HAVE_UACCESS_VALIDATION
+	bool
+	select OBJTOOL
+
 config HAVE_STACK_VALIDATION
 	bool
 	help

arch/x86/Kconfig

@@ -258,6 +258,7 @@ config X86
 	select HAVE_PREEMPT_DYNAMIC_CALL
 	select HAVE_RSEQ
 	select HAVE_SYSCALL_TRACEPOINTS
+	select HAVE_UACCESS_VALIDATION		if HAVE_OBJTOOL
 	select HAVE_UNSTABLE_SCHED_CLOCK
 	select HAVE_USER_RETURN_NOTIFIER
 	select HAVE_GENERIC_VDSO

scripts/Makefile.build

@@ -218,7 +218,7 @@ objtool_args =								\
 	$(if $(CONFIG_SLS), --sls)					\
 	$(if $(CONFIG_STACK_VALIDATION), --stackval)			\
 	$(if $(CONFIG_HAVE_STATIC_CALL_INLINE), --static-call)		\
-	--uaccess							\
+	$(if $(CONFIG_HAVE_UACCESS_VALIDATION), --uaccess)		\
 	$(if $(linked-object), --link)					\
 	$(if $(part-of-module), --module)				\
 	$(if $(CONFIG_GCOV_KERNEL), --no-unreachable)

scripts/link-vmlinux.sh

@@ -134,8 +134,10 @@ objtool_link()
 			objtoolopt="${objtoolopt} --static-call"
 		fi
 
+		if is_enabled CONFIG_HAVE_UACCESS_VALIDATION; then
 			objtoolopt="${objtoolopt} --uaccess"
 		fi
+	fi
 
 	if is_enabled CONFIG_NOINSTR_VALIDATION; then
 		objtoolopt="${objtoolopt} --noinstr"