[v3,1/2] x86/ubsan: Don't perform alignment checking on supporting compilers
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Message ID 20190627185620.4724-1-andrew.cooper3@citrix.com
State New, archived
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  • [v3,1/2] x86/ubsan: Don't perform alignment checking on supporting compilers
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Commit Message

Andrew Cooper June 27, 2019, 6:56 p.m. UTC
GCC 5 introduced -fsanitize=alignment which is enabled by default by
CONFIG_UBSAN.  This trips a load of wont-fix cases in the ACPI tables and the
hypercall page and stubs writing logic.

It also causes the native Xen boot to crash before the console is set up, for
an as-yet unidentified reason (most likley a wont-fix case earlier on boot).

Disable alignment sanitisation on compilers which would try using it.

Signed-off-by: Andrew Cooper <andrew.cooper3@citrix.com>
CC: Jan Beulich <JBeulich@suse.com>
CC: Wei Liu <wl@xen.org>
CC: Roger Pau Monné <roger.pau@citrix.com>
CC: Stefano Stabellini <sstabellini@kernel.org>
CC: Julien Grall <julien.grall@arm.com>

 * Avoid using -fno-sanitize=alignment for ARM
 * Use CFLAGS_UBSAN, initialised to empty first.
 * Leave a comment explaining why we use -fno-sanitize=alignment

The reason why x86 has a ifeq ($(CONFIG_UBSAN),y) is to avoid yet another
cc-option-add evaluated for every translation uint in the default case.  This
will all go away when we update to a recent version of Kconfig which moves all
the toolchain checks into that phase.
 xen/Rules.mk          | 8 +++++++-
 xen/arch/x86/Rules.mk | 8 ++++++++
 2 files changed, 15 insertions(+), 1 deletion(-)

diff mbox series

diff --git a/xen/Rules.mk b/xen/Rules.mk
index a151b3f625..3090ea7828 100644
--- a/xen/Rules.mk
+++ b/xen/Rules.mk
@@ -41,6 +41,9 @@  ALL_OBJS-y               += $(BASEDIR)/xsm/built_in.o
 ALL_OBJS-y               += $(BASEDIR)/arch/$(TARGET_ARCH)/built_in.o
 ALL_OBJS-$(CONFIG_CRYPTO)   += $(BASEDIR)/crypto/built_in.o
+# Initialise some variables
 ifeq ($(CONFIG_DEBUG),y)
 CFLAGS += -O1
@@ -138,7 +141,10 @@  $(filter-out %.init.o $(nocov-y),$(obj-y) $(obj-bin-y) $(extra-y)): CFLAGS += $(
 ifeq ($(CONFIG_UBSAN),y)
-$(filter-out %.init.o $(noubsan-y),$(obj-y) $(obj-bin-y) $(extra-y)): CFLAGS += -fsanitize=undefined
+CFLAGS_UBSAN += -fsanitize=undefined
+# Any -fno-sanitize= options need to come after any -fsanitize= options
+$(filter-out %.init.o $(noubsan-y),$(obj-y) $(obj-bin-y) $(extra-y)): \
+CFLAGS += $(filter-out -fno-%,$(CFLAGS_UBSAN)) $(filter -fno-%,$(CFLAGS_UBSAN))
 ifeq ($(CONFIG_LTO),y)
diff --git a/xen/arch/x86/Rules.mk b/xen/arch/x86/Rules.mk
index babc0edbcd..52e93afb48 100644
--- a/xen/arch/x86/Rules.mk
+++ b/xen/arch/x86/Rules.mk
@@ -57,6 +57,14 @@  endif
 $(call cc-option-add,CFLAGS-stack-boundary,CC,-mpreferred-stack-boundary=3)
 CFLAGS += $(CFLAGS-stack-boundary)
+ifeq ($(CONFIG_UBSAN),y)
+# Don't enable alignment sanitisation.  x86 has efficient unaligned accesses,
+# and various things (ACPI tables, hypercall pages, stubs, etc) are wont-fix.
+# It also causes an as-yet-unidentified crash on native boot before the
+# console starts.
+$(call cc-option-add,CFLAGS_UBSAN,CC,-fno-sanitize=alignment)
 # Set up the assembler include path properly for older toolchains.
 CFLAGS += -Wa,-I$(BASEDIR)/include