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.
It is necessary to check for both compiler and assembler support, as the
notrack prefix can be emitted in certain cases.
Signed-off-by: Andrew Cooper <andrew.coop...@citrix.com>
Acked-by: Jan Beulich <jbeul...@suse.com>
---
CC: Jan Beulich <jbeul...@suse.com>
CC: Roger Pau Monné <roger....@citrix.com>
CC: Wei Liu <w...@xen.org>
Clang/LLVM support for -mmanual-endbr is in progress:
https://reviews.llvm.org/D118355
v2:
* Correct CONFIG_HAS_CC_CET_IBT to CONFIG_XEN_IBT in some places
* Move cf_check compatibility into tools/tests/x86_emulator/x86-emulate.h
v3:
* Extend commit message
* Disable IBT for pvshim defconfig
---
Config.mk | 1 -
tools/firmware/Makefile | 2 ++
tools/libs/guest/xg_dom_decompress_unsafe.h | 2 ++
tools/tests/x86_emulator/x86-emulate.h | 2 ++
xen/arch/x86/Kconfig | 17 +++++++++++++++++
xen/arch/x86/arch.mk | 6 ++++++
xen/arch/x86/configs/pvshim_defconfig | 1 +
xen/arch/x86/include/asm/asm-defns.h | 6 ++++++
xen/arch/x86/include/asm/cpufeature.h | 1 +
xen/arch/x86/include/asm/cpufeatures.h | 1 +
xen/include/xen/compiler.h | 6 ++++++
11 files changed, 44 insertions(+), 1 deletion(-)
diff --git a/Config.mk b/Config.mk
index 95c053212ec3..f56f7dc33468 100644
--- a/Config.mk
+++ b/Config.mk
@@ -190,7 +190,6 @@ 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 345037b93b7f..53ed4f161edb 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/tools/libs/guest/xg_dom_decompress_unsafe.h
b/tools/libs/guest/xg_dom_decompress_unsafe.h
index 4e0bf23aa587..ac6b94288d5e 100644
--- a/tools/libs/guest/xg_dom_decompress_unsafe.h
+++ b/tools/libs/guest/xg_dom_decompress_unsafe.h
@@ -8,6 +8,8 @@ typedef int decompress_fn(unsigned char *inbuf, unsigned int
len,
void (*error)(const char *x));
#endif
+#define cf_check /* No Control Flow Integriy checking */
+
int xc_dom_decompress_unsafe(
decompress_fn fn, struct xc_dom_image *dom, void **blob, size_t *size)
__attribute__((visibility("internal")));
diff --git a/tools/tests/x86_emulator/x86-emulate.h
b/tools/tests/x86_emulator/x86-emulate.h
index 7f60ef9e89ba..18ae40d01712 100644
--- a/tools/tests/x86_emulator/x86-emulate.h
+++ b/tools/tests/x86_emulator/x86-emulate.h
@@ -54,6 +54,8 @@
#define likely(x) __builtin_expect(!!(x), true)
#define unlikely(x) __builtin_expect(!!(x), false)
+#define cf_check /* No Control Flow Integriy checking */
+
#define container_of(ptr, type, member) ({ \
typeof(((type *)0)->member) *mptr__ = (ptr); \
(type *)((char *)mptr__ - offsetof(type, member)); \
diff --git a/xen/arch/x86/Kconfig b/xen/arch/x86/Kconfig
index 41198b0f96ed..8e70f9a44847 100644
--- a/xen/arch/x86/Kconfig
+++ b/xen/arch/x86/Kconfig
@@ -40,6 +40,11 @@ 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) && $(as-instr,endbr64)
+
menu "Architecture Features"
source "arch/Kconfig"
@@ -125,6 +130,18 @@ config XEN_SHSTK
When CET-SS is active, 32bit PV guests cannot be used. Backwards
compatiblity can be provided via the PV Shim mechanism.
+config XEN_IBT
+ bool "Supervisor Indirect Branch Tracking"
+ depends on HAS_CC_CET_IBT
+ default y
+ help
+ Control-flow Enforcement Technology (CET) is a set of features in
+ hardware designed to combat Return-oriented Programming (ROP, also
+ call/jump COP/JOP) attacks. Indirect Branch Tracking is one CET
+ feature designed to provide function pointer protection.
+
+ This option arranges for Xen to use CET-IBT for its own protection.
+
config SHADOW_PAGING
bool "Shadow Paging"
default !PV_SHIM_EXCLUSIVE
diff --git a/xen/arch/x86/arch.mk b/xen/arch/x86/arch.mk
index edfc043dbbaf..f780c912a9cf 100644
--- a/xen/arch/x86/arch.mk
+++ b/xen/arch/x86/arch.mk
@@ -52,6 +52,12 @@ CFLAGS-$(CONFIG_CC_IS_GCC) += -fno-jump-tables
CFLAGS-$(CONFIG_CC_IS_CLANG) += -mretpoline-external-thunk
endif
+ifdef CONFIG_XEN_IBT
+CFLAGS += -fcf-protection=branch -mmanual-endbr
+else
+$(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/configs/pvshim_defconfig
b/xen/arch/x86/configs/pvshim_defconfig
index 787376df5a27..d0e92c2ded1f 100644
--- a/xen/arch/x86/configs/pvshim_defconfig
+++ b/xen/arch/x86/configs/pvshim_defconfig
@@ -8,6 +8,7 @@ CONFIG_NR_CPUS=32
CONFIG_EXPERT=y
# Disable features not used by the PV shim
# CONFIG_XEN_SHSTK is not set
+# CONFIG_XEN_IBT is not set
# CONFIG_GRANT_TABLE is not set
# CONFIG_HYPFS is not set
# CONFIG_BIGMEM is not set
diff --git a/xen/arch/x86/include/asm/asm-defns.h
b/xen/arch/x86/include/asm/asm-defns.h
index 505f39ad5f76..8bd9007731d5 100644
--- a/xen/arch/x86/include/asm/asm-defns.h
+++ b/xen/arch/x86/include/asm/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/arch/x86/include/asm/cpufeature.h
b/xen/arch/x86/include/asm/cpufeature.h
index a0ab6d7d78ea..f2c6f255ace9 100644
--- a/xen/arch/x86/include/asm/cpufeature.h
+++ b/xen/arch/x86/include/asm/cpufeature.h
@@ -152,6 +152,7 @@
#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/arch/x86/include/asm/cpufeatures.h
b/xen/arch/x86/include/asm/cpufeatures.h
index b10154fc44bb..7413febd7ad8 100644
--- a/xen/arch/x86/include/asm/cpufeatures.h
+++ b/xen/arch/x86/include/asm/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..933aec09a92d 100644
--- a/xen/include/xen/compiler.h
+++ b/xen/include/xen/compiler.h
@@ -37,6 +37,12 @@
# define nocall
#endif
+#ifdef CONFIG_XEN_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
