[PATCH v2 06/70] 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>

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
---
 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/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 ++++++
 10 files changed, 43 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..3bce0cfefb88 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
+
 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..c6819a417d05 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
+
 #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 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 fa7cf3844362..8b88f0240e85 100644
--- a/xen/arch/x86/arch.mk
+++ b/xen/arch/x86/arch.mk
@@ -47,6 +47,12 @@ CFLAGS-$(CONFIG_INDIRECT_THUNK) += 
-mindirect-branch=thunk-extern
 CFLAGS-$(CONFIG_INDIRECT_THUNK) += -mindirect-branch-register
 CFLAGS-$(CONFIG_INDIRECT_THUNK) += -fno-jump-tables
 
+ifdef CONFIG_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/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