From: Josh Poimboeuf <jpoimboe@xxxxxxxxxx>
[ Upstream commit e27e5bea956ce4d3eb15112de5fa5a3b77c2f488 ]
Add a macro which prevents a function from getting sealed if there are
no compile-time references to it.
Signed-off-by: Josh Poimboeuf <jpoimboe@xxxxxxxxxx>
Message-Id: <20220818213927.e44fmxkoq4yj6ybn@treble>
Signed-off-by: Paolo Bonzini <pbonzini@xxxxxxxxxx>
Signed-off-by: Sasha Levin <sashal@xxxxxxxxxx>
---
arch/x86/include/asm/ibt.h | 11 +++++++++++
tools/objtool/check.c | 3 ++-
2 files changed, 13 insertions(+), 1 deletion(-)
diff --git a/arch/x86/include/asm/ibt.h b/arch/x86/include/asm/ibt.h
index 689880eca9ba..9b08082a5d9f 100644
--- a/arch/x86/include/asm/ibt.h
+++ b/arch/x86/include/asm/ibt.h
@@ -31,6 +31,16 @@
#define __noendbr __attribute__((nocf_check))
+/*
+ * Create a dummy function pointer reference to prevent objtool from marking
+ * the function as needing to be "sealed" (i.e. ENDBR converted to NOP by
+ * apply_ibt_endbr()).
+ */
+#define IBT_NOSEAL(fname) \
+ ".pushsection .discard.ibt_endbr_noseal\n\t" \
+ _ASM_PTR fname "\n\t" \
+ ".popsection\n\t"
+
static inline __attribute_const__ u32 gen_endbr(void)
{
u32 endbr;
@@ -84,6 +94,7 @@ extern __noendbr void ibt_restore(u64 save);
#ifndef __ASSEMBLY__
#define ASM_ENDBR
+#define IBT_NOSEAL(name)
#define __noendbr
diff --git a/tools/objtool/check.c b/tools/objtool/check.c
index b341f8a8c7c5..31c719f99f66 100644
--- a/tools/objtool/check.c
+++ b/tools/objtool/check.c
@@ -4096,7 +4096,8 @@ static int validate_ibt(struct objtool_file *file)
* These sections can reference text addresses, but not with
* the intent to indirect branch to them.
*/
- if (!strncmp(sec->name, ".discard", 8) ||
+ if ((!strncmp(sec->name, ".discard", 8) &&
+ strcmp(sec->name, ".discard.ibt_endbr_noseal")) ||
!strncmp(sec->name, ".debug", 6) ||
!strcmp(sec->name, ".altinstructions") ||
!strcmp(sec->name, ".ibt_endbr_seal") ||
--
2.35.1
