linux-kernel - [PATCH 06/29] x86/ibt: Add ANNOTATE

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Date:   Fri, 18 Feb 2022 17:49:08 +0100
From:   Peter Zijlstra <peterz@...radead.org>
To:     x86@...nel.org, joao@...rdrivepizza.com, hjl.tools@...il.com,
        jpoimboe@...hat.com, andrew.cooper3@...rix.com
Cc:     linux-kernel@...r.kernel.org, peterz@...radead.org,
        ndesaulniers@...gle.com, keescook@...omium.org,
        samitolvanen@...gle.com, mark.rutland@....com,
        alyssa.milburn@...el.com
Subject: [PATCH 06/29] 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-coontrol-flow
instances -- consider text range checks, text patching, or return
trampolines etc.

Signed-off-by: Peter Zijlstra (Intel) <peterz@...radead.org>
---
 arch/x86/include/asm/linkage.h      |   11 +++++++++++
 include/linux/instruction_pointer.h |    5 +++++
 include/linux/objtool.h             |   13 +++++++++++++
 3 files changed, 29 insertions(+)

--- a/include/linux/objtool.h
+++ b/include/linux/objtool.h
@@ -78,6 +78,12 @@ 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__ */
 
 /*
@@ -130,6 +136,13 @@ struct unwind_hint {
 	.popsection
 .endm
 
+.macro ANNOTATE_NOENDBR
+.Lhere_\@:
+	.pushsection .discard.noendbr
+	.quad	.Lhere_\@
+	.popsection
+.endm
+
 #endif /* __ASSEMBLY__ */
 
 #else /* !CONFIG_STACK_VALIDATION */