Preserve bound registers for pointer pass/return

We need to save/restore bound registers and add a BND prefix before
branches in _dl_runtime_profile so that bound registers for pointer
pass and return are preserved when LD_AUDIT is used.

	[BZ #18134]
	* sysdeps/i386/configure.ac: Set HAVE_MPX_SUPPORT.
	* sysdeps/i386/configure: Regenerated.
	* sysdeps/i386/dl-trampoline.S (PRESERVE_BND_REGS_PREFIX): New.
	(_dl_runtime_profile): Save and restore Intel MPX return bound
	registers when calling _dl_call_pltexit.  Add
	PRESERVE_BND_REGS_PREFIX before return.
	* sysdeps/i386/link-defines.sym (LRV_BND0_OFFSET): New.
	(LRV_BND1_OFFSET): Likewise.
	* sysdeps/x86/bits/link.h (La_i86_retval): Add lrv_bnd0 and
	lrv_bnd1.
	* sysdeps/x86_64/dl-trampoline.S (_dl_runtime_profile): Fix
	typo in bndmov encoding.
	* sysdeps/x86_64/dl-trampoline.h: Properly save and restore
	Intel MPX bound registers.  Add PRESERVE_BND_REGS_PREFIX before
	branch instructions to preserve bounds.

4 files changed, 65 insertions, 0 deletions

diff --git a/sysdeps/i386/configure b/sysdeps/i386/configure
index 6e89b59..ab66c08 100644
--- a/sysdeps/i386/configure
+++ b/sysdeps/i386/configure
@@ -240,6 +240,33 @@ $as_echo "$libc_cv_cc_novzeroupper" >&6; }
 config_vars="$config_vars
 config-cflags-novzeroupper = $libc_cv_cc_novzeroupper"
 
+{ $as_echo "$as_me:${as_lineno-$LINENO}: checking for Intel MPX support" >&5
+$as_echo_n "checking for Intel MPX support... " >&6; }
+if ${libc_cv_asm_mpx+:} false; then :
+  $as_echo_n "(cached) " >&6
+else
+  cat > conftest.s <<\EOF
+        bndmov %bnd0,(%esp)
+EOF
+if { ac_try='${CC-cc} -c $ASFLAGS conftest.s 1>&5'
+  { { eval echo "\"\$as_me\":${as_lineno-$LINENO}: \"$ac_try\""; } >&5
+  (eval $ac_try) 2>&5
+  ac_status=$?
+  $as_echo "$as_me:${as_lineno-$LINENO}: \$? = $ac_status" >&5
+  test $ac_status = 0; }; }; then
+  libc_cv_asm_mpx=yes
+else
+  libc_cv_asm_mpx=no
+fi
+rm -f conftest*
+fi
+{ $as_echo "$as_me:${as_lineno-$LINENO}: result: $libc_cv_asm_mpx" >&5
+$as_echo "$libc_cv_asm_mpx" >&6; }
+if test $libc_cv_asm_mpx == yes; then
+  $as_echo "#define HAVE_MPX_SUPPORT 1" >>confdefs.h
+
+fi
+
 { $as_echo "$as_me:${as_lineno-$LINENO}: checking for AVX2 support" >&5
 $as_echo_n "checking for AVX2 support... " >&6; }
 if ${libc_cv_cc_avx2+:} false; then :
diff --git a/sysdeps/i386/configure.ac b/sysdeps/i386/configure.ac
index 35c4522..a3f3067 100644
--- a/sysdeps/i386/configure.ac
+++ b/sysdeps/i386/configure.ac
@@ -88,6 +88,21 @@ LIBC_TRY_CC_OPTION([-mno-vzeroupper],
 ])
 LIBC_CONFIG_VAR([config-cflags-novzeroupper], [$libc_cv_cc_novzeroupper])
 
+dnl Check whether asm supports Intel MPX
+AC_CACHE_CHECK(for Intel MPX support, libc_cv_asm_mpx, [dnl
+cat > conftest.s <<\EOF
+        bndmov %bnd0,(%esp)
+EOF
+if AC_TRY_COMMAND(${CC-cc} -c $ASFLAGS conftest.s 1>&AS_MESSAGE_LOG_FD); then
+  libc_cv_asm_mpx=yes
+else
+  libc_cv_asm_mpx=no
+fi
+rm -f conftest*])
+if test $libc_cv_asm_mpx == yes; then
+  AC_DEFINE(HAVE_MPX_SUPPORT)
+fi
+
 dnl Check if -mavx2 works.
 AC_CACHE_CHECK(for AVX2 support, libc_cv_cc_avx2, [dnl
 LIBC_TRY_CC_OPTION([-mavx2], [libc_cv_cc_avx2=yes], [libc_cv_cc_avx2=no])
diff --git a/sysdeps/i386/dl-trampoline.S b/sysdeps/i386/dl-trampoline.S
index 7c72b03..8a2fd8d 100644
--- a/sysdeps/i386/dl-trampoline.S
+++ b/sysdeps/i386/dl-trampoline.S
@@ -19,6 +19,12 @@
 #include <sysdep.h>
 #include <link-defines.h>
 
+#ifdef HAVE_MPX_SUPPORT
+# define PRESERVE_BND_REGS_PREFIX bnd
+#else
+# define PRESERVE_BND_REGS_PREFIX .byte 0xf2
+#endif
+
 	.text
 	.globl _dl_runtime_resolve
 	.type _dl_runtime_resolve, @function
@@ -172,6 +178,13 @@ _dl_runtime_profile:
 	movl %edx, LRV_EDX_OFFSET(%esp)
 	fstpt LRV_ST0_OFFSET(%esp)
 	fstpt LRV_ST1_OFFSET(%esp)
+#ifdef HAVE_MPX_SUPPORT
+	bndmov %bnd0, LRV_BND0_OFFSET(%esp)
+	bndmov %bnd1, LRV_BND1_OFFSET(%esp)
+#else
+	.byte 0x66,0x0f,0x1b,0x44,0x24,LRV_BND0_OFFSET
+	.byte 0x66,0x0f,0x1b,0x4c,0x24,LRV_BND1_OFFSET
+#endif
 	pushl %esp
 	cfi_adjust_cfa_offset (4)
 	# Address of La_i86_regs area.
@@ -185,9 +198,17 @@ _dl_runtime_profile:
 	movl LRV_EDX_OFFSET(%esp), %edx
 	fldt LRV_ST1_OFFSET(%esp)
 	fldt LRV_ST0_OFFSET(%esp)
+#ifdef HAVE_MPX_SUPPORT
+	bndmov LRV_BND0_OFFSET(%esp), %bnd0
+	bndmov LRV_BND1_OFFSET(%esp), %bnd1
+#else
+	.byte 0x66,0x0f,0x1a,0x44,0x24,LRV_BND0_OFFSET
+	.byte 0x66,0x0f,0x1a,0x4c,0x24,LRV_BND1_OFFSET
+#endif
 	# Restore stack before return.
 	addl $(LRV_SIZE + 4 + LR_SIZE + 4), %esp
 	cfi_adjust_cfa_offset (-(LRV_SIZE + 4 + LR_SIZE + 4))
+	PRESERVE_BND_REGS_PREFIX
 	ret
 	cfi_endproc
 	.size _dl_runtime_profile, .-_dl_runtime_profile
diff --git a/sysdeps/i386/link-defines.sym b/sysdeps/i386/link-defines.sym
index a63dcb9..0995adb 100644
--- a/sysdeps/i386/link-defines.sym
+++ b/sysdeps/i386/link-defines.sym
@@ -16,3 +16,5 @@ LRV_EAX_OFFSET		offsetof (struct La_i86_retval, lrv_eax)
 LRV_EDX_OFFSET		offsetof (struct La_i86_retval, lrv_edx)
 LRV_ST0_OFFSET		offsetof (struct La_i86_retval, lrv_st0)
 LRV_ST1_OFFSET		offsetof (struct La_i86_retval, lrv_st1)
+LRV_BND0_OFFSET		offsetof (struct La_i86_retval, lrv_bnd0)
+LRV_BND1_OFFSET		offsetof (struct La_i86_retval, lrv_bnd1)