linux-kernel - [PATCH 5/7] x86: Insert endbr32/endbr64 to vDSO

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Date:   Thu,  7 Jun 2018 07:38:53 -0700
From:   Yu-cheng Yu <yu-cheng.yu@...el.com>
To:     linux-kernel@...r.kernel.org, linux-doc@...r.kernel.org,
        linux-mm@...ck.org, linux-arch@...r.kernel.org, x86@...nel.org,
        "H. Peter Anvin" <hpa@...or.com>,
        Thomas Gleixner <tglx@...utronix.de>,
        Ingo Molnar <mingo@...hat.com>,
        "H.J. Lu" <hjl.tools@...il.com>,
        Vedvyas Shanbhogue <vedvyas.shanbhogue@...el.com>,
        "Ravi V. Shankar" <ravi.v.shankar@...el.com>,
        Dave Hansen <dave.hansen@...ux.intel.com>,
        Andy Lutomirski <luto@...capital.net>,
        Jonathan Corbet <corbet@....net>,
        Oleg Nesterov <oleg@...hat.com>, Arnd Bergmann <arnd@...db.de>,
        Mike Kravetz <mike.kravetz@...cle.com>
Subject: [PATCH 5/7] x86: Insert endbr32/endbr64 to vDSO

From: "H.J. Lu" <hjl.tools@...il.com>

When Intel indirect branch tracking is enabled, functions in vDSO which
may be called indirectly should have endbr32 or endbr64 as the first
instruction.  We try to compile vDSO with -fcf-protection=branch -mibt
if possible.  Otherwise, we insert endbr32 or endbr64 by hand to assembly
codes generated by the compiler.

Signed-off-by: H.J. Lu <hjl.tools@...il.com>
---
 arch/x86/entry/vdso/.gitignore |  4 ++++
 arch/x86/entry/vdso/Makefile   | 34 ++++++++++++++++++++++++++++++++++
 arch/x86/entry/vdso/endbr.sh   | 32 ++++++++++++++++++++++++++++++++
 3 files changed, 70 insertions(+)
 create mode 100644 arch/x86/entry/vdso/endbr.sh

diff --git a/arch/x86/entry/vdso/.gitignore b/arch/x86/entry/vdso/.gitignore
index aae8ffdd5880..552941fdfae0 100644
--- a/arch/x86/entry/vdso/.gitignore
+++ b/arch/x86/entry/vdso/.gitignore
@@ -5,3 +5,7 @@ vdso32-sysenter-syms.lds
 vdso32-int80-syms.lds
 vdso-image-*.c
 vdso2c
+vclock_gettime.S
+vgetcpu.S
+vclock_gettime.asm
+vgetcpu.asm
diff --git a/arch/x86/entry/vdso/Makefile b/arch/x86/entry/vdso/Makefile
index d998a487c9b1..cccafc36a831 100644
--- a/arch/x86/entry/vdso/Makefile
+++ b/arch/x86/entry/vdso/Makefile
@@ -118,6 +118,40 @@ $(obj)/%-x32.o: $(obj)/%.o FORCE
 
 targets += vdsox32.lds $(vobjx32s-y)
 
+ifdef CONFIG_X86_INTEL_BRANCH_TRACKING_USER
+  ifeq ($(call cc-option-yn, -fcf-protection=branch -mibt), y)
+    $(obj)/vclock_gettime.o $(obj)/vgetcpu.o $(obj)/vdso32/vclock_gettime.o: KBUILD_CFLAGS += -fcf-protection=branch -mibt
+  else
+    endbr := $(srctree)/$(src)/endbr.sh
+    quiet_cmd_endbr = ENDBR $@
+	  cmd_endbr = $(CONFIG_SHELL) '$(endbr)' $< $@
+
+    quiet_cmd_cc_asm_c = CC $(quiet_modtag) $@
+	  cmd_cc_asm_c = $(CC) $(c_flags) $(DISABLE_LTO) -S -o $@ $<
+
+$(obj)/%.asm: $(src)/%.c
+	$(call if_changed_dep,cc_asm_c)
+
+$(obj)/vclock_gettime.S: $(obj)/vclock_gettime.asm
+	$(call if_changed,endbr)
+
+$(obj)/vgetcpu.S: $(obj)/vgetcpu.asm
+	$(call if_changed,endbr)
+
+$(obj)/vclock_gettime.o: $(obj)/vclock_gettime.S
+	 $(call if_changed_rule,as_o_S)
+
+$(obj)/vgetcpu.o: $(obj)/vgetcpu.S
+	 $(call if_changed_rule,as_o_S)
+
+$(obj)/vdso32/vclock_gettime.S: $(obj)/vdso32/vclock_gettime.asm
+	$(call if_changed,endbr)
+
+$(obj)/vdso32/vclock_gettime.o: $(obj)/vdso32/vclock_gettime.S
+	 $(call if_changed_rule,as_o_S)
+  endif
+endif
+
 $(obj)/%.so: OBJCOPYFLAGS := -S
 $(obj)/%.so: $(obj)/%.so.dbg
 	$(call if_changed,objcopy)
diff --git a/arch/x86/entry/vdso/endbr.sh b/arch/x86/entry/vdso/endbr.sh
new file mode 100644
index 000000000000..983dbec182f2
--- /dev/null
+++ b/arch/x86/entry/vdso/endbr.sh
@@ -0,0 +1,32 @@
+#!/bin/sh
+# SPDX-License-Identifier: GPL-2.0
+
+in="$1"
+out="$2"
+
+case "$in" in
+*/vdso32/*)
+    endbr=".byte 0xf3,0x0f,0x1e,0xfb"
+    ;;
+*)
+    endbr=".byte 0xf3,0x0f,0x1e,0xfa"
+    ;;
+esac
+
+need_endbr=no
+while IFS= read line ; do
+   case "$line" in
+   __vdso_clock_gettime:|__vdso_getcpu:|__vdso_gettimeofday:|__vdso_time:)
+	need_endbr=yes
+	;;
+   "	."*)
+	;;
+   "	"*)
+	if [ "$need_endbr" = "yes" ]; then
+	    need_endbr=no
+	    echo "	$endbr"
+	fi
+	;;
+   esac
+   echo "$line"
+done < "$in" > "$out"
-- 
2.15.1