slirp 4.7 introduces a new CFI-friendly timer callback that does
not pass function pointers within libslirp as callbacks for timers.
Check the version number and, if it is new enough, allow using CFI
even with a system libslirp.

Signed-off-by: Paolo Bonzini <pbonzini@redhat.com>
---
 meson.build | 24 ++++++++++++------------
 1 file changed, 12 insertions(+), 12 deletions(-)

diff --git a/meson.build b/meson.build
index 861de93c4f..92a83580a3 100644
--- a/meson.build
+++ b/meson.build
@@ -2485,21 +2485,21 @@ if have_system
     slirp = declare_dependency(link_with: libslirp,
                                dependencies: slirp_deps,
                                include_directories: slirp_inc)
+  else
+    # slirp <4.7 is incompatible with CFI support in QEMU.  This is because
+    # it passes function pointers within libslirp as callbacks for timers.
+    # When using a system-wide shared libslirp, the type information for the
+    # callback is missing and the timer call produces a false positive with CFI.
+    #
+    # Now that slirp_opt has been defined, check if the selected slirp is compatible
+    # with control-flow integrity.
+    if get_option('cfi') and slirp.found() and slirp.version().version_compare('<4.7')
+      error('Control-Flow Integrity is not compatible with system-wide slirp.' \
+             + ' Please configure with --enable-slirp=git or upgrade to libslirp 4.7')
+    endif
   endif
 endif
 
-# For CFI, we need to compile slirp as a static library together with qemu.
-# This is because we register slirp functions as callbacks for QEMU Timers.
-# When using a system-wide shared libslirp, the type information for the
-# callback is missing and the timer call produces a false positive with CFI.
-#
-# Now that slirp_opt has been defined, check if the selected slirp is compatible
-# with control-flow integrity.
-if get_option('cfi') and slirp_opt == 'system'
-  error('Control-Flow Integrity is not compatible with system-wide slirp.' \
-         + ' Please configure with --enable-slirp=git')
-endif
-
 fdt = not_found
 if have_system
   fdt_opt = get_option('fdt')
-- 
2.35.1

Paolo Bonzini, le mar. 12 avril 2022 14:13:37 +0200, a ecrit:
> slirp 4.7 introduces a new CFI-friendly timer callback that does
> not pass function pointers within libslirp as callbacks for timers.
> Check the version number and, if it is new enough, allow using CFI
> even with a system libslirp.
> 
> Signed-off-by: Paolo Bonzini <pbonzini@redhat.com>

Reviewed-by: Samuel Thibault <samuel.thibault@ens-lyon.org>

> ---
>  meson.build | 24 ++++++++++++------------
>  1 file changed, 12 insertions(+), 12 deletions(-)
> 
> diff --git a/meson.build b/meson.build
> index 861de93c4f..92a83580a3 100644
> --- a/meson.build
> +++ b/meson.build
> @@ -2485,21 +2485,21 @@ if have_system
>      slirp = declare_dependency(link_with: libslirp,
>                                 dependencies: slirp_deps,
>                                 include_directories: slirp_inc)
> +  else
> +    # slirp <4.7 is incompatible with CFI support in QEMU.  This is because
> +    # it passes function pointers within libslirp as callbacks for timers.
> +    # When using a system-wide shared libslirp, the type information for the
> +    # callback is missing and the timer call produces a false positive with CFI.
> +    #
> +    # Now that slirp_opt has been defined, check if the selected slirp is compatible
> +    # with control-flow integrity.
> +    if get_option('cfi') and slirp.found() and slirp.version().version_compare('<4.7')
> +      error('Control-Flow Integrity is not compatible with system-wide slirp.' \
> +             + ' Please configure with --enable-slirp=git or upgrade to libslirp 4.7')
> +    endif
>    endif
>  endif
>  
> -# For CFI, we need to compile slirp as a static library together with qemu.
> -# This is because we register slirp functions as callbacks for QEMU Timers.
> -# When using a system-wide shared libslirp, the type information for the
> -# callback is missing and the timer call produces a false positive with CFI.
> -#
> -# Now that slirp_opt has been defined, check if the selected slirp is compatible
> -# with control-flow integrity.
> -if get_option('cfi') and slirp_opt == 'system'
> -  error('Control-Flow Integrity is not compatible with system-wide slirp.' \
> -         + ' Please configure with --enable-slirp=git')
> -endif
> -
>  fdt = not_found
>  if have_system
>    fdt_opt = get_option('fdt')
> -- 
> 2.35.1
> 

-- 
Samuel
---
Pour une évaluation indépendante, transparente et rigoureuse !
Je soutiens la Commission d'Évaluation de l'Inria.