[PATCH 01/65] x86: Introduce support for CET-IBT

[Andrew Cooper <andrew.cooper3@xxxxxxxxxx>]

CET Indirect Branch Tracking is a hardware feature designed to provide
forward-edge control flow integrity, protecting against jump/call oriented
programming.

IBT requires the placement of ENDBR{32,64} instructions at the target of every
indirect call/jmp, and every entrypoint.

However, the default -fcf-protection=branch places an ENDBR on every function
which far more than necessary, and reduces the quantity of protection
afforded.  Therefore, we use manual placement using the cf_check attribute.

Signed-off-by: Andrew Cooper <andrew.cooper3@xxxxxxxxxx>
---
CC: Jan Beulich <JBeulich@xxxxxxxx>
CC: Roger Pau Monné <roger.pau@xxxxxxxxxx>
CC: Wei Liu <wl@xxxxxxx>
---
 Config.mk                              |  1 -
 tools/firmware/Makefile                |  2 ++
 xen/arch/x86/Kconfig                   | 17 +++++++++++++++++
 xen/arch/x86/arch.mk                   |  6 ++++++
 xen/arch/x86/x86_emulate/x86_emulate.h |  5 +++++
 xen/include/asm-x86/asm-defns.h        |  6 ++++++
 xen/include/asm-x86/cpufeature.h       |  1 +
 xen/include/asm-x86/cpufeatures.h      |  1 +
 xen/include/xen/compiler.h             |  6 ++++++
 9 files changed, 44 insertions(+), 1 deletion(-)

diff --git a/Config.mk b/Config.mk
index 6587c7d626c9..508261a7dcf4 100644
--- a/Config.mk
+++ b/Config.mk
@@ -199,7 +199,6 @@ APPEND_CFLAGS += $(foreach i, $(APPEND_INCLUDES), -I$(i))
 
 EMBEDDED_EXTRA_CFLAGS := -nopie -fno-stack-protector -fno-stack-protector-all
 EMBEDDED_EXTRA_CFLAGS += -fno-exceptions -fno-asynchronous-unwind-tables
-EMBEDDED_EXTRA_CFLAGS += -fcf-protection=none
 
 XEN_EXTFILES_URL ?= http://xenbits.xen.org/xen-extfiles
 # All the files at that location were downloaded from elsewhere on
diff --git a/tools/firmware/Makefile b/tools/firmware/Makefile
index 1f2711779400..b2fd73248604 100644
--- a/tools/firmware/Makefile
+++ b/tools/firmware/Makefile
@@ -6,6 +6,8 @@ TARGET      := hvmloader/hvmloader
 INST_DIR := $(DESTDIR)$(XENFIRMWAREDIR)
 DEBG_DIR := $(DESTDIR)$(DEBUG_DIR)$(XENFIRMWAREDIR)
 
+EMBEDDED_EXTRA_CFLAGS += -fcf-protection=none
+
 SUBDIRS-y :=
 SUBDIRS-$(CONFIG_OVMF) += ovmf-dir
 SUBDIRS-$(CONFIG_SEABIOS) += seabios-dir
diff --git a/xen/arch/x86/Kconfig b/xen/arch/x86/Kconfig
index b4abfca46f6a..8b7ad0145b29 100644
--- a/xen/arch/x86/Kconfig
+++ b/xen/arch/x86/Kconfig
@@ -39,6 +39,11 @@ config HAS_AS_CET_SS
        # binutils >= 2.29 or LLVM >= 6
        def_bool $(as-instr,wrssq %rax$(comma)0;setssbsy)
 
+config HAS_CC_CET_IBT
+       # GCC >= 9 and binutils >= 2.29
+       # Retpoline check to work around 
https://gcc.gnu.org/bugzilla/show_bug.cgi?id=93654
+       def_bool $(cc-option,-fcf-protection=branch -mmanual-endbr 
-mindirect-branch=thunk-extern) && $(as-instr,endbr64)
+
 menu "Architecture Features"
 
 source "arch/Kconfig"
@@ -124,6 +129,18 @@ config XEN_SHSTK
          When CET-SS is active, 32bit PV guests cannot be used.  Backwards
          compatiblity can be provided via the PV Shim mechanism.
 
+config XEN_IBT
+       bool "Supervisor Indirect Branch Tracking"
+       depends on HAS_CC_CET_IBT
+       default y
+       help
+         Control-flow Enforcement Technology (CET) is a set of features in
+         hardware designed to combat Return-oriented Programming (ROP, also
+         call/jump COP/JOP) attacks.  Indirect Branch Tracking is one CET
+         feature designed to provide function pointer protection.
+
+         This option arranges for Xen to use CET-IBT for its own protection.
+
 config SHADOW_PAGING
        bool "Shadow Paging"
        default !PV_SHIM_EXCLUSIVE
diff --git a/xen/arch/x86/arch.mk b/xen/arch/x86/arch.mk
index ce0c1a0e7fb2..1c8381f7c9d8 100644
--- a/xen/arch/x86/arch.mk
+++ b/xen/arch/x86/arch.mk
@@ -46,6 +46,12 @@ CFLAGS-$(CONFIG_INDIRECT_THUNK) += 
-mindirect-branch=thunk-extern
 CFLAGS-$(CONFIG_INDIRECT_THUNK) += -mindirect-branch-register
 CFLAGS-$(CONFIG_INDIRECT_THUNK) += -fno-jump-tables
 
+ifdef CONFIG_HAS_CC_CET_IBT
+CFLAGS += -fcf-protection=branch -mmanual-endbr
+else
+$(call cc-option-add,CFLAGS,CC,-fcf-protection=none)
+endif
+
 # If supported by the compiler, reduce stack alignment to 8 bytes. But allow
 # this to be overridden elsewhere.
 $(call cc-option-add,CFLAGS-stack-boundary,CC,-mpreferred-stack-boundary=3)
diff --git a/xen/arch/x86/x86_emulate/x86_emulate.h 
b/xen/arch/x86/x86_emulate/x86_emulate.h
index d8fb3a990933..4a483a464804 100644
--- a/xen/arch/x86/x86_emulate/x86_emulate.h
+++ b/xen/arch/x86/x86_emulate/x86_emulate.h
@@ -35,6 +35,11 @@
 # error Unknown compilation width
 #endif
 
+#ifndef cf_check
+/* Cope with userspace build not knowing about CET-IBT */
+#define cf_check
+#endif
+
 struct x86_emulate_ctxt;
 
 /*
diff --git a/xen/include/asm-x86/asm-defns.h b/xen/include/asm-x86/asm-defns.h
index 505f39ad5f76..8bd9007731d5 100644
--- a/xen/include/asm-x86/asm-defns.h
+++ b/xen/include/asm-x86/asm-defns.h
@@ -57,6 +57,12 @@
     INDIRECT_BRANCH jmp \arg
 .endm
 
+#ifdef CONFIG_XEN_IBT
+# define ENDBR64 endbr64
+#else
+# define ENDBR64
+#endif
+
 .macro guest_access_mask_ptr ptr:req, scratch1:req, scratch2:req
 #if defined(CONFIG_SPECULATIVE_HARDEN_GUEST_ACCESS)
     /*
diff --git a/xen/include/asm-x86/cpufeature.h b/xen/include/asm-x86/cpufeature.h
index 4754940e23f3..d9e1cd87f0fb 100644
--- a/xen/include/asm-x86/cpufeature.h
+++ b/xen/include/asm-x86/cpufeature.h
@@ -151,6 +151,7 @@
 #define cpu_has_nscb            boot_cpu_has(X86_FEATURE_NSCB)
 #define cpu_has_xen_lbr         boot_cpu_has(X86_FEATURE_XEN_LBR)
 #define cpu_has_xen_shstk       boot_cpu_has(X86_FEATURE_XEN_SHSTK)
+#define cpu_has_xen_ibt         boot_cpu_has(X86_FEATURE_XEN_IBT)
 
 #define cpu_has_msr_tsc_aux     (cpu_has_rdtscp || cpu_has_rdpid)
 
diff --git a/xen/include/asm-x86/cpufeatures.h 
b/xen/include/asm-x86/cpufeatures.h
index b10154fc44bb..7413febd7ad8 100644
--- a/xen/include/asm-x86/cpufeatures.h
+++ b/xen/include/asm-x86/cpufeatures.h
@@ -39,6 +39,7 @@ XEN_CPUFEATURE(SC_VERW_PV,        X86_SYNTH(23)) /* VERW used 
by Xen for PV */
 XEN_CPUFEATURE(SC_VERW_HVM,       X86_SYNTH(24)) /* VERW used by Xen for HVM */
 XEN_CPUFEATURE(SC_VERW_IDLE,      X86_SYNTH(25)) /* VERW used by Xen for idle 
*/
 XEN_CPUFEATURE(XEN_SHSTK,         X86_SYNTH(26)) /* Xen uses CET Shadow Stacks 
*/
+XEN_CPUFEATURE(XEN_IBT,           X86_SYNTH(27)) /* Xen uses CET Indirect 
Branch Tracking */
 
 /* Bug words follow the synthetic words. */
 #define X86_NR_BUG 1
diff --git a/xen/include/xen/compiler.h b/xen/include/xen/compiler.h
index 696c7eb89e4c..575036f44b3b 100644
--- a/xen/include/xen/compiler.h
+++ b/xen/include/xen/compiler.h
@@ -37,6 +37,12 @@
 # define nocall
 #endif
 
+#ifdef CONFIG_HAS_CC_CET_IBT
+# define cf_check     __attribute__((__cf_check__))
+#else
+# define cf_check
+#endif
+
 #if (!defined(__clang__) && (__GNUC__ == 4) && (__GNUC_MINOR__ < 5))
 #define unreachable() do {} while (1)
 #else
-- 
2.11.0