Re: [RFC PATCH 4/4] net: slirp: allow CFI with libslirp >= 4.7

[Samuel Thibault <samuel.thibault@gnu.org>]

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
---
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