From 524a8ef2ad76af8ac049293d993a1856b0d888fb Mon Sep 17 00:00:00 2001
From: Nick Alcock <nick.alcock@oracle.com>
Date: Mon, 26 Dec 2016 10:08:57 +0100
Subject: [PATCH] PLT avoidance for __stack_chk_fail [BZ #7065]

Add a hidden __stack_chk_fail_local alias to libc.so,
and make sure that on targets which use __stack_chk_fail,
this does not introduce a local PLT reference into libc.so.
---
 ChangeLog                      | 14 ++++++++++++++
 debug/Makefile                 |  6 ++++++
 debug/stack_chk_fail.c         |  2 ++
 sysdeps/generic/symbol-hacks.h | 12 ++++++++++++
 4 files changed, 34 insertions(+)

diff --git a/ChangeLog b/ChangeLog
index 5e3e64a3da..10d5a37718 100644
--- a/ChangeLog
+++ b/ChangeLog
@@ -1,3 +1,17 @@
+2016-12-26  Nick Alcock  <nick.alcock@oracle.com>
+	    Adhemerval Zanella  <adhemerval.zanella@linaro.org>
+	    Florian Weimer  <fweimer@redhat.com>
+
+	[BZ #7065]
+	PLT avoidance for __stack_chk_fail*.
+	* debug/Makefile (CFLAGS-stack_chk_fail.c)
+	(CFLAGS-stack_chk_fail_local.c): Build without stack protector.
+	* debug/stack_chk_fail.c (__stack_chk_fail): Add
+	__stack_chk_fail_local alias.
+	* sysdeps/generic/symbol-hacks.h [IS_IN (libc)]
+	(__stack_chk_fail): Turn into hidden reference to
+	__stack_chk_fail_local.
+
 2016-12-26  Nick Alcock  <nick.alcock@oracle.com>
 
 	[BZ #7065]
diff --git a/debug/Makefile b/debug/Makefile
index 84d3f92c0d..ed7c39793b 100644
--- a/debug/Makefile
+++ b/debug/Makefile
@@ -53,6 +53,12 @@ routines  = backtrace backtracesyms backtracesymsfd noophooks \
 	    $(static-only-routines)
 static-only-routines := warning-nop stack_chk_fail_local
 
+# Building the stack-protector failure routines with stack protection
+# makes no sense.
+
+CFLAGS-stack_chk_fail.c = $(no-stack-protector)
+CFLAGS-stack_chk_fail_local.c = $(no-stack-protector)
+
 CFLAGS-backtrace.c = -fno-omit-frame-pointer
 CFLAGS-sprintf_chk.c = $(libio-mtsafe)
 CFLAGS-snprintf_chk.c = $(libio-mtsafe)
diff --git a/debug/stack_chk_fail.c b/debug/stack_chk_fail.c
index 4d0796f78c..5db0886170 100644
--- a/debug/stack_chk_fail.c
+++ b/debug/stack_chk_fail.c
@@ -27,3 +27,5 @@ __stack_chk_fail (void)
 {
   __fortify_fail ("stack smashing detected");
 }
+
+strong_alias (__stack_chk_fail, __stack_chk_fail_local)
diff --git a/sysdeps/generic/symbol-hacks.h b/sysdeps/generic/symbol-hacks.h
index ce576c9fd2..d614c099c9 100644
--- a/sysdeps/generic/symbol-hacks.h
+++ b/sysdeps/generic/symbol-hacks.h
@@ -4,4 +4,16 @@
 asm ("memmove = __GI_memmove");
 asm ("memset = __GI_memset");
 asm ("memcpy = __GI_memcpy");
+
+/* Some targets do not use __stack_chk_fail_local.  In libc.so,
+   redirect __stack_chk_fail to a hidden reference
+   __stack_chk_fail_local, to avoid the PLT reference.
+   __stack_chk_fail itself is a global symbol, exported from libc.so,
+   and cannot be made hidden.  */
+
+# if IS_IN (libc) && defined SHARED && \
+  defined STACK_PROTECTOR_LEVEL && STACK_PROTECTOR_LEVEL > 0
+asm (".hidden __stack_chk_fail_local\n"
+     "__stack_chk_fail = __stack_chk_fail_local");
+# endif
 #endif