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[PATCH 07/24] i386: Add _CET_ENDBR to indirect jump targets in add_n.S/sub_n.S

From: "H.J. Lu" <hjl dot tools at gmail dot com>
To: libc-alpha at sourceware dot org
Date: Wed, 13 Jun 2018 08:31:50 -0700
Subject: [PATCH 07/24] i386: Add _CET_ENDBR to indirect jump targets in add_n.S/sub_n.S
References: <20180613153207.57232-1-hjl.tools@gmail.com>
i386 add_n.S and sub_n.S use a trick to implment jump tables with LEA.
We can't use conditional branches nor normal jump tables since jump
table entries use EFLAGS set by jump table index.  This patch adds
_CET_ENDBR to indirect jump targets and adjust destination for
_CET_ENDBR.

	* sysdeps/i386/add_n.S: Include <sysdep.h>, instead of
	"sysdep.h".
	(__mpn_add_n): Save and restore %ebx if IBT is enabed.  Add
	_CET_ENDBR to indirect jump targets and adjust jump destination
	for _CET_ENDBR.
	* sysdeps/i386/i686/add_n.S: Include <sysdep.h>, instead of
	"sysdep.h".
	(__mpn_add_n): Save and restore %ebx if IBT is enabed.  Add
	_CET_ENDBR to indirect jump targets and adjust jump destination
	for _CET_ENDBR.
	* sysdeps/i386/sub_n.S: Include <sysdep.h>, instead of
	"sysdep.h".
	(__mpn_sub_n): Save and restore %ebx if IBT is enabed.  Add
	_CET_ENDBR to indirect jump targets and adjust jump destination
	for _CET_ENDBR.
---
 sysdeps/i386/add_n.S      | 27 ++++++++++++++++++++++++++-
 sysdeps/i386/i686/add_n.S | 27 ++++++++++++++++++++++++++-
 sysdeps/i386/sub_n.S      | 26 +++++++++++++++++++++++++-
 3 files changed, 77 insertions(+), 3 deletions(-)

diff --git a/sysdeps/i386/add_n.S b/sysdeps/i386/add_n.S
index d6a35237b0..d3805ba213 100644
--- a/sysdeps/i386/add_n.S
+++ b/sysdeps/i386/add_n.S
@@ -17,7 +17,7 @@
    along with the GNU MP Library; see the file COPYING.LIB.  If not,
    see <http://www.gnu.org/licenses/>.  */
 
-#include "sysdep.h"
+#include <sysdep.h>
 #include "asm-syntax.h"
 
 #define PARMS	4+8	/* space for 2 saved regs */
@@ -40,6 +40,13 @@ ENTRY (__mpn_add_n)
 	cfi_rel_offset (esi, 0)
 	movl S2(%esp),%edx
 	movl SIZE(%esp),%ecx
+
+#if defined __CET__ && (__CET__ & 1) != 0
+	pushl	%ebx
+	cfi_adjust_cfa_offset (4)
+	cfi_rel_offset (ebx, 0)
+#endif
+
 	movl	%ecx,%eax
 	shrl	$3,%ecx			/* compute count for unrolled loop */
 	negl	%eax
@@ -51,6 +58,9 @@ ENTRY (__mpn_add_n)
 	subl	%eax,%esi		/* ... by a constant when we ... */
 	subl	%eax,%edx		/* ... enter the loop */
 	shrl	$2,%eax			/* restore previous value */
+#if defined __CET__ && (__CET__ & 1) != 0
+	leal	-4(,%eax,4),%ebx	/* Count for 4-byte endbr32 */
+#endif
 #ifdef PIC
 /* Calculate start address in loop for PIC.  Due to limitations in some
    assemblers, Loop-L0-3 cannot be put into the leal */
@@ -64,30 +74,40 @@ L(0):	leal	(%eax,%eax,8),%eax
 #else
 /* Calculate start address in loop for non-PIC.  */
  	leal	(L(oop) - 3)(%eax,%eax,8),%eax
+#endif
+#if defined __CET__ && (__CET__ & 1) != 0
+	addl	%ebx,%eax		/* Adjust for endbr32 */
 #endif
 	jmp	*%eax			/* jump into loop */
 	ALIGN (3)
 L(oop):	movl	(%esi),%eax
 	adcl	(%edx),%eax
 	movl	%eax,(%edi)
+	_CET_ENDBR
 	movl	4(%esi),%eax
 	adcl	4(%edx),%eax
 	movl	%eax,4(%edi)
+	_CET_ENDBR
 	movl	8(%esi),%eax
 	adcl	8(%edx),%eax
 	movl	%eax,8(%edi)
+	_CET_ENDBR
 	movl	12(%esi),%eax
 	adcl	12(%edx),%eax
 	movl	%eax,12(%edi)
+	_CET_ENDBR
 	movl	16(%esi),%eax
 	adcl	16(%edx),%eax
 	movl	%eax,16(%edi)
+	_CET_ENDBR
 	movl	20(%esi),%eax
 	adcl	20(%edx),%eax
 	movl	%eax,20(%edi)
+	_CET_ENDBR
 	movl	24(%esi),%eax
 	adcl	24(%edx),%eax
 	movl	%eax,24(%edi)
+	_CET_ENDBR
 	movl	28(%esi),%eax
 	adcl	28(%edx),%eax
 	movl	%eax,28(%edi)
@@ -100,6 +120,11 @@ L(oop):	movl	(%esi),%eax
 	sbbl	%eax,%eax
 	negl	%eax
 
+#if defined __CET__ && (__CET__ & 1) != 0
+	popl	%ebx
+	cfi_adjust_cfa_offset (-4)
+	cfi_restore (ebx)
+#endif
 	popl %esi
 	cfi_adjust_cfa_offset (-4)
 	cfi_restore (esi)
diff --git a/sysdeps/i386/i686/add_n.S b/sysdeps/i386/i686/add_n.S
index 5c6c1448d6..d2d532cd30 100644
--- a/sysdeps/i386/i686/add_n.S
+++ b/sysdeps/i386/i686/add_n.S
@@ -17,7 +17,7 @@
    along with the GNU MP Library; see the file COPYING.LIB.  If not,
    see <http://www.gnu.org/licenses/>.  */
 
-#include "sysdep.h"
+#include <sysdep.h>
 #include "asm-syntax.h"
 
 #define PARMS	4+8		/* space for 2 saved regs */
@@ -44,6 +44,13 @@ ENTRY (__mpn_add_n)
 	cfi_rel_offset (esi, 0)
 	movl	S2(%esp),%edx
 	movl	SIZE(%esp),%ecx
+
+#if defined __CET__ && (__CET__ & 1) != 0
+	pushl	%ebx
+	cfi_adjust_cfa_offset (4)
+	cfi_rel_offset (ebx, 0)
+#endif
+
 	movl	%ecx,%eax
 	shrl	$3,%ecx			/* compute count for unrolled loop */
 	negl	%eax
@@ -55,6 +62,9 @@ ENTRY (__mpn_add_n)
 	subl	%eax,%esi		/* ... by a constant when we ... */
 	subl	%eax,%edx		/* ... enter the loop */
 	shrl	$2,%eax			/* restore previous value */
+#if defined __CET__ && (__CET__ & 1) != 0
+	leal	-4(,%eax,4),%ebx	/* Count for 4-byte endbr32 */
+#endif
 #ifdef PIC
 /* Calculate start address in loop for PIC.  */
 	leal	(L(oop)-L(0)-3)(%eax,%eax,8),%eax
@@ -63,30 +73,40 @@ L(0):
 #else
 /* Calculate start address in loop for non-PIC.  */
  	leal	(L(oop) - 3)(%eax,%eax,8),%eax
+#endif
+#if defined __CET__ && (__CET__ & 1) != 0
+	addl	%ebx,%eax		/* Adjust for endbr32 */
 #endif
 	jmp	*%eax			/* jump into loop */
 	ALIGN (3)
 L(oop):	movl	(%esi),%eax
 	adcl	(%edx),%eax
 	movl	%eax,(%edi)
+	_CET_ENDBR
 	movl	4(%esi),%eax
 	adcl	4(%edx),%eax
 	movl	%eax,4(%edi)
+	_CET_ENDBR
 	movl	8(%esi),%eax
 	adcl	8(%edx),%eax
 	movl	%eax,8(%edi)
+	_CET_ENDBR
 	movl	12(%esi),%eax
 	adcl	12(%edx),%eax
 	movl	%eax,12(%edi)
+	_CET_ENDBR
 	movl	16(%esi),%eax
 	adcl	16(%edx),%eax
 	movl	%eax,16(%edi)
+	_CET_ENDBR
 	movl	20(%esi),%eax
 	adcl	20(%edx),%eax
 	movl	%eax,20(%edi)
+	_CET_ENDBR
 	movl	24(%esi),%eax
 	adcl	24(%edx),%eax
 	movl	%eax,24(%edi)
+	_CET_ENDBR
 	movl	28(%esi),%eax
 	adcl	28(%edx),%eax
 	movl	%eax,28(%edi)
@@ -99,6 +119,11 @@ L(oop):	movl	(%esi),%eax
 	sbbl	%eax,%eax
 	negl	%eax
 
+#if defined __CET__ && (__CET__ & 1) != 0
+	popl	%ebx
+	cfi_adjust_cfa_offset (-4)
+	cfi_restore (ebx)
+#endif
 	popl %esi
 	cfi_adjust_cfa_offset (-4)
 	cfi_restore (esi)
diff --git a/sysdeps/i386/sub_n.S b/sysdeps/i386/sub_n.S
index 7c6f48c32e..8f321b8c6c 100644
--- a/sysdeps/i386/sub_n.S
+++ b/sysdeps/i386/sub_n.S
@@ -17,7 +17,7 @@
    along with the GNU MP Library; see the file COPYING.LIB.  If not,
    see <http://www.gnu.org/licenses/>.  */
 
-#include "sysdep.h"
+#include <sysdep.h>
 #include "asm-syntax.h"
 
 #define PARMS	4+8		/* space for 2 saved regs */
@@ -40,6 +40,13 @@ ENTRY (__mpn_sub_n)
 	cfi_rel_offset (esi, 0)
 	movl	S2(%esp),%edx
 	movl	SIZE(%esp),%ecx
+
+#if defined __CET__ && (__CET__ & 1) != 0
+	pushl	%ebx
+	cfi_adjust_cfa_offset (4)
+	cfi_rel_offset (ebx, 0)
+#endif
+
 	movl	%ecx,%eax
 	shrl	$3,%ecx			/* compute count for unrolled loop */
 	negl	%eax
@@ -51,6 +58,9 @@ ENTRY (__mpn_sub_n)
 	subl	%eax,%esi		/* ... by a constant when we ... */
 	subl	%eax,%edx		/* ... enter the loop */
 	shrl	$2,%eax			/* restore previous value */
+#if defined __CET__ && (__CET__ & 1) != 0
+	leal	-4(,%eax,4),%ebx	/* Count for 4-byte endbr32 */
+#endif
 #ifdef PIC
 /* Calculate start address in loop for PIC.  Due to limitations in some
    assemblers, Loop-L0-3 cannot be put into the leal */
@@ -64,30 +74,39 @@ L(0):	leal	(%eax,%eax,8),%eax
 #else
 /* Calculate start address in loop for non-PIC.  */
  	leal	(L(oop) - 3)(%eax,%eax,8),%eax
+#endif
+#if defined __CET__ && (__CET__ & 1) != 0
+	addl	%ebx,%eax		/* Adjust for endbr32 */
 #endif
 	jmp	*%eax			/* jump into loop */
 	ALIGN (3)
 L(oop):	movl	(%esi),%eax
 	sbbl	(%edx),%eax
 	movl	%eax,(%edi)
+	_CET_ENDBR
 	movl	4(%esi),%eax
 	sbbl	4(%edx),%eax
 	movl	%eax,4(%edi)
+	_CET_ENDBR
 	movl	8(%esi),%eax
 	sbbl	8(%edx),%eax
 	movl	%eax,8(%edi)
 	movl	12(%esi),%eax
 	sbbl	12(%edx),%eax
 	movl	%eax,12(%edi)
+	_CET_ENDBR
 	movl	16(%esi),%eax
 	sbbl	16(%edx),%eax
 	movl	%eax,16(%edi)
+	_CET_ENDBR
 	movl	20(%esi),%eax
 	sbbl	20(%edx),%eax
 	movl	%eax,20(%edi)
+	_CET_ENDBR
 	movl	24(%esi),%eax
 	sbbl	24(%edx),%eax
 	movl	%eax,24(%edi)
+	_CET_ENDBR
 	movl	28(%esi),%eax
 	sbbl	28(%edx),%eax
 	movl	%eax,28(%edi)
@@ -100,6 +119,11 @@ L(oop):	movl	(%esi),%eax
 	sbbl	%eax,%eax
 	negl	%eax
 
+#if defined __CET__ && (__CET__ & 1) != 0
+	popl	%ebx
+	cfi_adjust_cfa_offset (-4)
+	cfi_restore (ebx)
+#endif
 	popl %esi
 	cfi_adjust_cfa_offset (-4)
 	cfi_restore (esi)
-- 
2.17.1
References:
- [PATCH-V2: 00/24] CET: Prepare for CET enabling
  - From: H.J. Lu
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