x86/ibt: Add ANNOTATE_NOENDBR

In order to have objtool warn about code references to !ENDBR
instruction, we need an annotation to allow this for non-control-flow
instances -- consider text range checks, text patching, or return
trampolines etc.

Signed-off-by: Peter Zijlstra (Intel) <peterz@infradead.org>
Reviewed-by: Kees Cook <keescook@chromium.org>
Acked-by: Josh Poimboeuf <jpoimboe@redhat.com>
Link: https://lore.kernel.org/r/20220308154317.578968224@infradead.org

Author: Peter Zijlstra

include/linux/objtool.h

@@ -77,6 +77,12 @@ struct unwind_hint {
 #define STACK_FRAME_NON_STANDARD_FP(func)
 #endif
 
+#define ANNOTATE_NOENDBR					\
+	"986: \n\t"						\
+	".pushsection .discard.noendbr\n\t"			\
+	_ASM_PTR " 986b\n\t"					\
+	".popsection\n\t"
+
 #else /* __ASSEMBLY__ */
 
 /*
@@ -129,6 +135,13 @@ struct unwind_hint {
 	.popsection
 .endm
 
+.macro ANNOTATE_NOENDBR
+.Lhere_\@:
+	.pushsection .discard.noendbr
+	.quad	.Lhere_\@
+	.popsection
+.endm
+
 #endif /* __ASSEMBLY__ */
 
 #else /* !CONFIG_STACK_VALIDATION */
@@ -139,12 +152,15 @@ struct unwind_hint {
 	"\n\t"
 #define STACK_FRAME_NON_STANDARD(func)
 #define STACK_FRAME_NON_STANDARD_FP(func)
+#define ANNOTATE_NOENDBR
 #else
 #define ANNOTATE_INTRA_FUNCTION_CALL
 .macro UNWIND_HINT sp_reg:req sp_offset=0 type:req end=0
 .endm
 .macro STACK_FRAME_NON_STANDARD func:req
 .endm
+.macro ANNOTATE_NOENDBR
+.endm
 #endif
 
 #endif /* CONFIG_STACK_VALIDATION */

tools/include/linux/objtool.h

@@ -77,6 +77,12 @@ struct unwind_hint {
 #define STACK_FRAME_NON_STANDARD_FP(func)
 #endif
 
+#define ANNOTATE_NOENDBR					\
+	"986: \n\t"						\
+	".pushsection .discard.noendbr\n\t"			\
+	_ASM_PTR " 986b\n\t"					\
+	".popsection\n\t"
+
 #else /* __ASSEMBLY__ */
 
 /*
@@ -129,6 +135,13 @@ struct unwind_hint {
 	.popsection
 .endm
 
+.macro ANNOTATE_NOENDBR
+.Lhere_\@:
+	.pushsection .discard.noendbr
+	.quad	.Lhere_\@
+	.popsection
+.endm
+
 #endif /* __ASSEMBLY__ */
 
 #else /* !CONFIG_STACK_VALIDATION */
@@ -139,12 +152,15 @@ struct unwind_hint {
 	"\n\t"
 #define STACK_FRAME_NON_STANDARD(func)
 #define STACK_FRAME_NON_STANDARD_FP(func)
+#define ANNOTATE_NOENDBR
 #else
 #define ANNOTATE_INTRA_FUNCTION_CALL
 .macro UNWIND_HINT sp_reg:req sp_offset=0 type:req end=0
 .endm
 .macro STACK_FRAME_NON_STANDARD func:req
 .endm
+.macro ANNOTATE_NOENDBR
+.endm
 #endif
 
 #endif /* CONFIG_STACK_VALIDATION */