x86: Use control flow typechecking where possible

Now all indirect branch targets have been annotated, turn on typechecking to
catch issues in the future.

This extension isn't in a released version of GCC yet, so provide a container
to use with the extension included, and add it to CI.  RANDCONFIG is necessary
because some stubs for compiled-out subsystems are used as function pointer
targets.

Signed-off-by: Andrew Cooper <andrew.cooper3@citrix.com>
Acked-by: Jan Beulich <jbeulich@suse.com>

automation/build/debian/buster-gcc-ibt.dockerfile

@@ -0,0 +1,66 @@
+FROM debian:buster-slim AS builder
+
+ENV DEBIAN_FRONTEND=noninteractive
+ENV USER root
+
+RUN apt-get update && \
+    apt-get --quiet --yes install \
+        bison \
+        build-essential \
+        flex \
+        libc6-dev-i386 \
+        libgmp-dev \
+        libisl-dev \
+        libmpc-dev \
+        libmpfr-dev \
+        patch \
+        wget
+
+RUN mkdir /build
+WORKDIR /build
+
+RUN wget -q https://ftp.gnu.org/gnu/gcc/gcc-11.2.0/gcc-11.2.0.tar.xz -O - | tar xJ --strip=1
+RUN wget -q https://xenbits.xen.org/people/andrewcoop/gcc-11.2-Add-fcf-check-attribute-yes-no.patch -O - | patch -p1
+RUN ./configure \
+        --prefix=/opt/gcc-11-ibt \
+        --enable-languages=c \
+        --disable-nls \
+        --disable-threads \
+        --disable-bootstrap \
+        --disable-shared \
+        --disable-libmudflap \
+        --disable-libssp \
+        --disable-libgomp \
+        --disable-decimal-float \
+        --disable-libquadmath \
+        --disable-libatomic \
+        --disable-libcc1 \
+        --disable-libmpx
+RUN make -j`nproc` && make -j`nproc` install
+
+
+FROM debian:buster-slim
+COPY --from=builder /opt/gcc-11-ibt /opt/gcc-11-ibt
+
+LABEL maintainer.name="The Xen Project" \
+      maintainer.email="xen-devel@lists.xenproject.org"
+
+ENV DEBIAN_FRONTEND=noninteractive
+ENV USER root
+ENV PATH="/opt/gcc-11-ibt/bin:${PATH}"
+
+RUN mkdir /build
+WORKDIR /build
+
+RUN apt-get update && \
+    apt-get --quiet --yes install \
+        bison \
+        checkpolicy \
+        flex \
+        gawk \
+        make \
+        python3 \
+        && \
+        apt-get autoremove -y && \
+        apt-get clean && \
+        rm -rf /var/lib/apt/lists* /tmp/* /var/tmp/*

automation/gitlab-ci/build.yaml

@@ -294,6 +294,12 @@ debian-stretch-32-gcc-debug:
   variables:
     CONTAINER: debian:stretch-i386
 
+debian-buster-gcc-ibt:
+  extends: .gcc-x86-64-build
+  variables:
+    CONTAINER: debian:buster-gcc-ibt
+    RANDCONFIG: y
+
 debian-unstable-clang:
   extends: .clang-x86-64-build
   variables:

automation/scripts/containerize

@@ -33,6 +33,7 @@ case "_${CONTAINER}" in
     _focal) CONTAINER="${BASE}/ubuntu:focal" ;;
     _jessie) CONTAINER="${BASE}/debian:jessie" ;;
     _stretch|_) CONTAINER="${BASE}/debian:stretch" ;;
+    _buster-gcc-ibt) CONTAINER="${BASE}/debian:buster-gcc-ibt" ;;
     _unstable|_) CONTAINER="${BASE}/debian:unstable" ;;
     _trusty) CONTAINER="${BASE}/ubuntu:trusty" ;;
     _xenial) CONTAINER="${BASE}/ubuntu:xenial" ;;

xen/arch/x86/arch.mk

@@ -54,6 +54,7 @@ endif
 
 ifdef CONFIG_XEN_IBT
 CFLAGS += -fcf-protection=branch -mmanual-endbr
+$(call cc-option-add,CFLAGS,CC,-fcf-check-attribute=no)
 else
 $(call cc-option-add,CFLAGS,CC,-fcf-protection=none)
 endif