Makefile: tools/check-postbuild.sh: add postbuild script

When compiling SYZOS into the executor binary, the compiler often
attempts to emit a jump table, putting it into the data section of
the executor. SYZOS is unable to access that data and crashes.

Introduce a script that validates the arm64 executor by scanning
its `guest` section for the ADRP instructions.
In the future, this script can be extended to perform other types
of checks.

Author: ramosian-glider

Makefile

@@ -134,6 +134,7 @@ else
 	$(CXX) -o ./bin/$(TARGETOS)_$(TARGETARCH)/syz-executor$(EXE) executor/executor.cc \
 		$(ADDCXXFLAGS) $(CXXFLAGS) $(LDFLAGS) -DGOOS_$(TARGETOS)=1 -DGOARCH_$(TARGETARCH)=1 \
 		-DHOSTGOOS_$(HOSTOS)=1 -DGIT_REVISION=\"$(REV)\"
+	tools/check-postbuild.sh $(TARGETOS) $(TARGETARCH) ./bin/$(TARGETOS)_$(TARGETARCH)/syz-executor$(EXE) $(CXX)
 endif
 endif
 endif

tools/check-postbuild.sh

@@ -0,0 +1,55 @@
+#!/bin/bash
+# Post-build validation for syzkaller binaries.
+
+target_os="$1"; shift
+target_arch="$1"; shift
+executor_binary="$1"; shift
+cxx_binary="$1"; shift
+
+function get_objdump_for_arm64() {
+  local compiler_binary="$1"
+  local objdump_binary=""
+
+  case "${compiler_binary}" in
+    "aarch64-linux-gnu-g++")
+      objdump_binary="aarch64-linux-gnu-objdump"
+      ;;
+    "g++")
+      objdump_binary="objdump"
+      ;;
+    clang++-[0-9]*)
+      # Extract the version number part
+      version="${compiler_binary#clang++-}"
+      objdump_binary="llvm-objdump-$version"
+      ;;
+    "clang++")
+      objdump_binary="llvm-objdump"
+      ;;
+    *)
+      # Default
+      echo "Error: Unknown compiler binary '${compiler_binary}'" >&2
+      objdump_binary=""
+      ;;
+  esac
+
+  echo "${objdump_binary}"
+}
+
+function validate_arm64_guest_code() {
+  local section="guest"
+  local objdump_bin=$(get_objdump_for_arm64 ${cxx_binary})
+  local objdump_tmp=$(mktemp -t objdump_output.XXXXXX)
+  trap "rm -f \"${objdump_tmp}\"" EXIT
+  ${objdump_bin} -d -j ${section} ${executor_binary} >${objdump_tmp} 2>&1 || exit 1
+  ( cat ${objdump_tmp} | grep "\<adrp\>" > /dev/null ) &&
+    echo "Postbuild error: found ADRP in executor's '${section}' section!" && exit 1
+  return 0
+}
+
+# For now, we only validate Linux binaries.
+[ "${target_os}" != "linux" ] && exit 0
+
+# For now, we only validate ARM64 binaries.
+[ "${target_arch}" != "arm64" ] && exit 0
+
+validate_arm64_guest_code