RFR [XS] 8234809: set relro in linker flags when building with gcc - was RE: binary Hardening on linux using Relocation Read-Only (relro)

[Baesken, Matthias]

> Hello Erik, Florian ,  currently   relro  is set already  for libjvm.
> I think if this works nicely  for libjvm, it shouldn't do any harm to set it as well
> in the BASIC_LDFLAGS  for other binaries .
> I would propose a patch like :

Hello,  here is my webrev , please review .

Bug/webrev :

https://bugs.openjdk.java.net/browse/JDK-8234809

http://cr.openjdk.java.net/~mbaesken/webrevs/8234809.0/


Thanks, Matthias

> 
> > I would  involve at least hotspot-dev for a wider discussion on this as libjvm
> is
> > the most affected library.
> 
> Hello Erik, Florian ,  currently   relro  is set already  for libjvm.
> I think if this works nicely  for libjvm, it shouldn't do any harm to set it as well
> in the BASIC_LDFLAGS  for other binaries .
> I would propose a patch like :
> 
> diff -r 80e1201f6c9a make/autoconf/flags-ldflags.m4
> --- a/make/autoconf/flags-ldflags.m4    Fri Nov 22 09:06:35 2019 -0500
> +++ b/make/autoconf/flags-ldflags.m4    Tue Nov 26 13:05:42 2019 +0100
> @@ -70,10 +70,9 @@
>      fi
> 
>      # Add -z defs, to forbid undefined symbols in object files.
> -    BASIC_LDFLAGS="$BASIC_LDFLAGS -Wl,-z,defs"
> -
> -    BASIC_LDFLAGS_JVM_ONLY="-Wl,-O1 -Wl,-z,relro"
> -
> +    # add relro (mark relocations read only) for all libs
> +    BASIC_LDFLAGS="$BASIC_LDFLAGS -Wl,-z,defs -Wl,-z,relro"
> +    BASIC_LDFLAGS_JVM_ONLY="-Wl,-O1"
> 
> 
> If I understand
> https://bugzilla.redhat.com/show_bug.cgi?id=1571359
> correct, RedHat is setting those flags already  via the build system .
> 
> Regarding  "bindnow"  (ld -z now) ,   this might be set  additionally   by using --
> with-extra-ldflags .
> 
> 
> Best regards, Matthias
> 
> 
> > Hello,
> >
> > I wasn't directly involved in introducing these flags, but my
> > understanding is that it's always a performance compromise. I would
> > involve at least hotspot-dev for a wider discussion on this as libjvm is
> > the most affected library.
> >
> > /Erik
> >
> > On 2019-11-25 06:42, Baesken, Matthias wrote:
> > > Hello,   I wonder why  the  binary hardening  on linux  using Relocation
> > Read-Only (relro)  is not enabled by default.
> > >
> > > Some info can be found here :
> > >
> > > https://wiki.debian.org/Hardening
> > >
> > > https://www.redhat.com/en/blog/hardening-elf-binaries-using-
> > relocation-read-only-relro
> > >
> > >
> > > Currently I  notice  the settings only  for debug  / fastdebug builds , see
> > flags-ldflags.m4 :
> > >
> > >    # Setup debug level-dependent LDFLAGS
> > >    if test "x$TOOLCHAIN_TYPE" = xgcc; then
> > >      if test "x$OPENJDK_TARGET_OS" = xlinux; then
> > >        if test x$DEBUG_LEVEL = xrelease; then
> > >
> > DEBUGLEVEL_LDFLAGS_JDK_ONLY="$DEBUGLEVEL_LDFLAGS_JDK_ONLY -
> > Wl,-O1"
> > >        else
> > >          # mark relocations read only on (fast/slow) debug builds
> > >          DEBUGLEVEL_LDFLAGS_JDK_ONLY="-Wl,-z,relro"
> > >        fi
> > >        if test x$DEBUG_LEVEL = xslowdebug; then
> > >          # do relocations at load
> > >          DEBUGLEVEL_LDFLAGS="-Wl,-z,now"
> > >        fi
> > >      fi
> > >
> > > Shouldn't we use  at least  "-Wl,-z,relro" also on product builds ?
> > >
> > > For  "-Wl,-z,now"   some  startup  performance hits are mentioned in
> > articles/blogs -  any experiences / performance-measurements   with this
> in
> > the OpenJDK  context ?
> > >
> > > Best regards, Matthias
> > >