From 2582080f19e8fe9c1204dfb6fecf744311f00777 Mon Sep 17 00:00:00 2001
From: "H.J. Lu" <hjl.tools@gmail.com>
Date: Thu, 14 Jul 2022 10:31:21 -0700
Subject: [PATCH] x86: Disable sibcall if indirect_return attribute doesn't
 match

When shadow stack is enabled, function with indirect_return attribute
may return via indirect jump.  In this case, we need to disable sibcall
if caller doesn't have indirect_return attribute and indirect branch
tracking is enabled since compiler won't generate ENDBR when calling the
caller.

gcc/

	PR target/85620
	* config/i386/i386.cc (ix86_function_ok_for_sibcall): Return
	false if callee has indirect_return attribute and caller
	doesn't.

gcc/testsuite/

	PR target/85620
	* gcc.target/i386/pr85620-2.c: Updated.
	* gcc.target/i386/pr85620-5.c: New test.
	* gcc.target/i386/pr85620-6.c: Likewise.
	* gcc.target/i386/pr85620-7.c: Likewise.
---
 gcc/config/i386/i386.cc                   | 10 ++++++++++
 gcc/testsuite/gcc.target/i386/pr85620-2.c |  3 ++-
 gcc/testsuite/gcc.target/i386/pr85620-5.c | 13 +++++++++++++
 gcc/testsuite/gcc.target/i386/pr85620-6.c | 14 ++++++++++++++
 gcc/testsuite/gcc.target/i386/pr85620-7.c | 14 ++++++++++++++
 5 files changed, 53 insertions(+), 1 deletion(-)
 create mode 100644 gcc/testsuite/gcc.target/i386/pr85620-5.c
 create mode 100644 gcc/testsuite/gcc.target/i386/pr85620-6.c
 create mode 100644 gcc/testsuite/gcc.target/i386/pr85620-7.c

diff --git a/gcc/config/i386/i386.cc b/gcc/config/i386/i386.cc
index 3a3c729..e03f86d 100644
--- a/gcc/config/i386/i386.cc
+++ b/gcc/config/i386/i386.cc
@@ -1024,6 +1024,16 @@ ix86_function_ok_for_sibcall (tree decl, tree exp)
 	 return false;
     }
 
+  /* Disable sibcall if callee has indirect_return attribute and
+     caller doesn't since callee will return to the caller's caller
+     via an indirect jump.  */
+  if (((flag_cf_protection & (CF_RETURN | CF_BRANCH))
+       == (CF_RETURN | CF_BRANCH))
+      && lookup_attribute ("indirect_return", TYPE_ATTRIBUTES (type))
+      && !lookup_attribute ("indirect_return",
+			    TYPE_ATTRIBUTES (TREE_TYPE (cfun->decl))))
+    return false;
+
   /* Otherwise okay.  That also includes certain types of indirect calls.  */
   return true;
 }
diff --git a/gcc/testsuite/gcc.target/i386/pr85620-2.c b/gcc/testsuite/gcc.target/i386/pr85620-2.c
index b2e680f..14ce0ff 100644
--- a/gcc/testsuite/gcc.target/i386/pr85620-2.c
+++ b/gcc/testsuite/gcc.target/i386/pr85620-2.c
@@ -1,6 +1,7 @@
 /* { dg-do compile } */
 /* { dg-options "-O2 -fcf-protection" } */
-/* { dg-final { scan-assembler-times {\mendbr} 1 } } */
+/* { dg-final { scan-assembler-times {\mendbr} 2 } } */
+/* { dg-final { scan-assembler-not "jmp" } } */
 
 struct ucontext;
 
diff --git a/gcc/testsuite/gcc.target/i386/pr85620-5.c b/gcc/testsuite/gcc.target/i386/pr85620-5.c
new file mode 100644
index 0000000..0453770
--- /dev/null
+++ b/gcc/testsuite/gcc.target/i386/pr85620-5.c
@@ -0,0 +1,13 @@
+/* { dg-do compile } */
+/* { dg-options "-O2 -fcf-protection" } */
+/* { dg-final { scan-assembler-not "jmp" } } */
+
+struct ucontext;
+
+extern int (*bar) (struct ucontext *) __attribute__((__indirect_return__));
+
+int
+foo (struct ucontext *oucp)
+{
+  return bar (oucp);
+}
diff --git a/gcc/testsuite/gcc.target/i386/pr85620-6.c b/gcc/testsuite/gcc.target/i386/pr85620-6.c
new file mode 100644
index 0000000..0b6a64e
--- /dev/null
+++ b/gcc/testsuite/gcc.target/i386/pr85620-6.c
@@ -0,0 +1,14 @@
+/* { dg-do compile } */
+/* { dg-options "-O2 -fcf-protection" } */
+/* { dg-final { scan-assembler "jmp" } } */
+
+struct ucontext;
+
+extern int bar (struct ucontext *) __attribute__((__indirect_return__));
+
+__attribute__((__indirect_return__))
+int
+foo (struct ucontext *oucp)
+{
+  return bar (oucp);
+}
diff --git a/gcc/testsuite/gcc.target/i386/pr85620-7.c b/gcc/testsuite/gcc.target/i386/pr85620-7.c
new file mode 100644
index 0000000..fa62d56
--- /dev/null
+++ b/gcc/testsuite/gcc.target/i386/pr85620-7.c
@@ -0,0 +1,14 @@
+/* { dg-do compile } */
+/* { dg-options "-O2 -fcf-protection" } */
+/* { dg-final { scan-assembler "jmp" } } */
+
+struct ucontext;
+
+extern int (*bar) (struct ucontext *) __attribute__((__indirect_return__));
+extern int foo (struct ucontext *) __attribute__((__indirect_return__));
+
+int
+foo (struct ucontext *oucp)
+{
+  return bar (oucp);
+}
-- 
2.7.4