Re: [PATCH 2/4] debian: Enable CET on amd64

From: Dave Chinner <david@fromorbit.com>
To: Bastian Germann <bastiangermann@fishpost.de>
Cc: linux-xfs@vger.kernel.org, Dimitri John Ledkov <xnox@ubuntu.com>
Subject: Re: [PATCH 2/4] debian: Enable CET on amd64
Date: Sun, 21 Feb 2021 14:59:43 +1100	[thread overview]
Message-ID: <20210221035943.GJ4662@dread.disaster.area> (raw)
In-Reply-To: <20210220121610.3982-3-bastiangermann@fishpost.de>

On Sat, Feb 20, 2021 at 01:16:07PM +0100, Bastian Germann wrote:
> This is a change introduced in 5.6.0-1ubuntu3.
> 
> Reported-by: Dimitri John Ledkov <xnox@ubuntu.com>
> Signed-off-by: Bastian Germann <bastiangermann@fishpost.de>
> ---
>  debian/changelog | 1 +
>  debian/rules     | 8 +++++++-
>  2 files changed, 8 insertions(+), 1 deletion(-)
> 
> diff --git a/debian/changelog b/debian/changelog
> index 8320a2e8..c77f04ab 100644
> --- a/debian/changelog
> +++ b/debian/changelog
> @@ -2,6 +2,7 @@ xfsprogs (5.11.0-rc0-1) experimental; urgency=medium
>  
>    [ Dimitri John Ledkov ]
>    * Drop trying to create upstream distribution
> +  * Enable CET on amd64
>  
>   -- Bastian Germann <bastiangermann@fishpost.de>  Sat, 20 Feb 2021 11:57:31 +0100
>  
> diff --git a/debian/rules b/debian/rules
> index 8a3345b6..dd093f2c 100755
> --- a/debian/rules
> +++ b/debian/rules
> @@ -23,8 +23,14 @@ pkgdev = DIST_ROOT=`pwd`/$(dirdev); export DIST_ROOT;
>  pkgdi  = DIST_ROOT=`pwd`/$(dirdi); export DIST_ROOT;
>  stdenv = @GZIP=-q; export GZIP;
>  
> +ifeq ($(target),amd64)
> +export DEB_CFLAGS_MAINT_APPEND=-fcf-protection
> +export DEB_LDFLAGS_MAINT_APPEND=-fcf-protection
> +endif
> +include /usr/share/dpkg/default.mk
> +
>  options = export DEBUG=-DNDEBUG DISTRIBUTION=debian \
> -	  INSTALL_USER=root INSTALL_GROUP=root \
> +	  INSTALL_USER=root INSTALL_GROUP=root LDFLAGS='$(LDFLAGS)' \
>  	  LOCAL_CONFIGURE_OPTIONS="--enable-editline=yes --enable-blkid=yes --disable-ubsan --disable-addrsan --disable-threadsan --enable-lto" ;
>  diopts  = $(options) \
>  	  export OPTIMIZER=-Os LOCAL_CONFIGURE_OPTIONS="--enable-gettext=no --disable-ubsan --disable-addrsan --disable-threadsan --enable-lto" ;

No. This is not the way to turn on build wide compiler/linker
options/protections.

IOWs, if you want to turn on control flow protections to make ROP
exploits harder (why that actually matters for xfsprogs is beyond
me), then it you need to add a configure option similar to
--enable-lto. Then it can actually be enabled and used by other
distros, not just Ubuntu, and it will also ensure that builds will
fail at configure time if the compiler/linker does not support this
functionality.

Cheers,

Dave.
-- 
Dave Chinner
david@fromorbit.com