configure,meson: support Control-Flow Integrity

This patch adds a flag to enable/disable control flow integrity checks
on indirect function calls.
This feature only allows indirect function calls at runtime to functions
with compatible signatures.

This feature is only provided by LLVM/Clang, and depends on link-time
optimization which is currently supported only with LLVM/Clang >= 6.0

We also add an option to enable a debugging version of cfi, with verbose
output in case of a CFI violation.

CFI on indirect function calls does not support calls to functions in
shared libraries (since they were not known at compile time), and such
calls are forbidden. QEMU relies on dlopen/dlsym when using modules,
so we make modules incompatible with CFI.

All the checks are performed in meson.build. configure is only used to
forward the flags to meson

Signed-off-by: Daniele Buono <dbuono@linux.vnet.ibm.com>
Message-Id: <20201204230615.2392-5-dbuono@linux.vnet.ibm.com>
Signed-off-by: Paolo Bonzini <pbonzini@redhat.com>

configure

@@ -411,6 +411,8 @@ coroutine=""
 coroutine_pool="$default_feature"
 debug_stack_usage="no"
 crypto_afalg="no"
+cfi="false"
+cfi_debug="false"
 seccomp="$default_feature"
 glusterfs="$default_feature"
 glusterfs_xlator_opt="no"
@@ -1195,6 +1197,16 @@ for opt do
   ;;
   --disable-safe-stack) safe_stack="no"
   ;;
+  --enable-cfi)
+      cfi="true";
+      lto="true";
+  ;;
+  --disable-cfi) cfi="false"
+  ;;
+  --enable-cfi-debug) cfi_debug="true"
+  ;;
+  --disable-cfi-debug) cfi_debug="false"
+  ;;
   --disable-curses) curses="disabled"
   ;;
   --enable-curses) curses="enabled"
@@ -1788,7 +1800,13 @@ disabled with --disable-FEATURE, default is enabled if available
   sparse          sparse checker
   safe-stack      SafeStack Stack Smash Protection. Depends on
                   clang/llvm >= 3.7 and requires coroutine backend ucontext.
-
+  cfi             Enable Control-Flow Integrity for indirect function calls.
+                  In case of a cfi violation, QEMU is terminated with SIGILL
+                  Depends on lto and is incompatible with modules
+                  Automatically enables Link-Time Optimization (lto)
+  cfi-debug       In case of a cfi violation, a message containing the line that
+                  triggered the error is written to stderr. After the error,
+                  QEMU is still terminated with SIGILL
   gnutls          GNUTLS cryptography support
   nettle          nettle cryptography support
   gcrypt          libgcrypt cryptography support
@@ -6971,7 +6989,7 @@ NINJA=$ninja $meson setup \
         -Db_pie=$(if test "$pie" = yes; then echo true; else echo false; fi) \
         ${staticpic:+-Db_staticpic=$staticpic} \
         -Db_coverage=$(if test "$gcov" = yes; then echo true; else echo false; fi) \
-        -Db_lto=$lto \
+        -Db_lto=$lto -Dcfi=$cfi -Dcfi_debug=$cfi_debug \
         -Dmalloc=$malloc -Dmalloc_trim=$malloc_trim -Dsparse=$sparse \
         -Dkvm=$kvm -Dhax=$hax -Dwhpx=$whpx -Dhvf=$hvf \
         -Dxen=$xen -Dxen_pci_passthrough=$xen_pci_passthrough -Dtcg=$tcg \

meson.build

@@ -773,6 +773,7 @@ elif get_option('vhost_user_blk_server').disabled() or not have_system
     have_vhost_user_blk_server = false
 endif
 
+
 if get_option('fuse').disabled() and get_option('fuse_lseek').enabled()
   error('Cannot enable fuse-lseek while fuse is disabled')
 endif
@@ -795,6 +796,46 @@ if not get_option('fuse_lseek').disabled()
   endif
 endif
 
+if get_option('cfi')
+  cfi_flags=[]
+  # Check for dependency on LTO
+  if not get_option('b_lto')
+    error('Selected Control-Flow Integrity but LTO is disabled')
+  endif
+  if config_host.has_key('CONFIG_MODULES')
+    error('Selected Control-Flow Integrity is not compatible with modules')
+  endif
+  # Check for cfi flags. CFI requires LTO so we can't use
+  # get_supported_arguments, but need a more complex "compiles" which allows
+  # custom arguments
+  if cc.compiles('int main () { return 0; }', name: '-fsanitize=cfi-icall',
+                 args: ['-flto', '-fsanitize=cfi-icall'] )
+    cfi_flags += '-fsanitize=cfi-icall'
+  else
+    error('-fsanitize=cfi-icall is not supported by the compiler')
+  endif
+  if cc.compiles('int main () { return 0; }',
+                 name: '-fsanitize-cfi-icall-generalize-pointers',
+                 args: ['-flto', '-fsanitize=cfi-icall',
+                        '-fsanitize-cfi-icall-generalize-pointers'] )
+    cfi_flags += '-fsanitize-cfi-icall-generalize-pointers'
+  else
+    error('-fsanitize-cfi-icall-generalize-pointers is not supported by the compiler')
+  endif
+  if get_option('cfi_debug')
+    if cc.compiles('int main () { return 0; }',
+                   name: '-fno-sanitize-trap=cfi-icall',
+                   args: ['-flto', '-fsanitize=cfi-icall',
+                          '-fno-sanitize-trap=cfi-icall'] )
+      cfi_flags += '-fno-sanitize-trap=cfi-icall'
+    else
+      error('-fno-sanitize-trap=cfi-icall is not supported by the compiler')
+    endif
+  endif
+  add_project_arguments(cfi_flags, native: false, language: ['c', 'cpp', 'objc'])
+  add_project_link_arguments(cfi_flags, native: false, language: ['c', 'cpp', 'objc'])
+endif
+
 #################
 # config-host.h #
 #################
@@ -831,6 +872,7 @@ config_host_data.set('CONFIG_MALLOC_TRIM', has_malloc_trim)
 config_host_data.set('CONFIG_STATX', has_statx)
 config_host_data.set('CONFIG_FUSE', fuse.found())
 config_host_data.set('CONFIG_FUSE_LSEEK', fuse_lseek.found())
+config_host_data.set('CONFIG_CFI', get_option('cfi'))
 config_host_data.set('QEMU_VERSION', '"@0@"'.format(meson.project_version()))
 config_host_data.set('QEMU_VERSION_MAJOR', meson.project_version().split('.')[0])
 config_host_data.set('QEMU_VERSION_MINOR', meson.project_version().split('.')[1])
@@ -2195,6 +2237,8 @@ if targetos == 'windows'
   summary_info += {'QGA MSI support':   config_host.has_key('CONFIG_QGA_MSI')}
 endif
 summary_info += {'seccomp support':   config_host.has_key('CONFIG_SECCOMP')}
+summary_info += {'CFI support':       get_option('cfi')}
+summary_info += {'CFI debug support': get_option('cfi_debug')}
 summary_info += {'coroutine backend': config_host['CONFIG_COROUTINE_BACKEND']}
 summary_info += {'coroutine pool':    config_host['CONFIG_COROUTINE_POOL'] == '1'}
 summary_info += {'debug stack usage': config_host.has_key('CONFIG_DEBUG_STACK_USAGE')}

meson_options.txt

@@ -35,6 +35,10 @@ option('xen_pci_passthrough', type: 'feature', value: 'auto',
        description: 'Xen PCI passthrough support')
 option('tcg', type: 'feature', value: 'auto',
        description: 'TCG support')
+option('cfi', type: 'boolean', value: 'false',
+       description: 'Control-Flow Integrity (CFI)')
+option('cfi_debug', type: 'boolean', value: 'false',
+       description: 'Verbose errors in case of CFI violation')
 
 option('cocoa', type : 'feature', value : 'auto',
        description: 'Cocoa user interface (macOS only)')