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

[Erik Joelsson]

Looks good.

/Erik

On 2019-11-26 05:07, Baesken, Matthias wrote:

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