ETDYN guide

- +ETDYN guide The PaX Team @@ -27,6 +27,7 @@ These guidelines are required to achieve full Address S= pace Layout Randomization =20 Introduction +

One of the features of PaX is Address Space Layout Randomization (= ASLR) that allows the kernel to randomize the addresses of various areas in @@ -67,10 +68,12 @@ These guidelines are required to achieve full Address= Space Layout Randomization themselves in the future.

=20 +

=20 How to produce ET_DYN ELF executables +

=20

The following discussion assumes that the GNU toolchain (such as g= cc and @@ -114,8 +117,8 @@ These guidelines are required to achieve full Address= Space Layout Randomization care about gcrt1.o). It is no coincidence that crt1.o is not linked i= nto shared libraries as this object contains (among others) the low-level= entry point and startup code that invokes the C library startup code which = in - turn calls main().=20 - Initiating the building of ET_DYN executables on Gentoo does no= t require us to put -shared in our CFLAGS or LDFLAGS

+ turn calls main().

+ Initiating the building of ET_DYN executables on Gentoo does no= t require us to put -shared in our CFLAGS or LDFLAGS =20

Making crt1.o position independent is easy, we just have to make u= se of the GOT (in keeping with the tradition of the glibc naming convention for= the @@ -148,20 +151,22 @@ These guidelines are required to achieve full Addre= ss Space Layout Randomization code) they can be compiled once and put into the same directory where the other systemwide crt* files are.

=20 ET_DYN ELF executables (The Gentoo Way) +

=20 -

On Gentoo this is accomplished by merging hardened-gcc: +

On Gentoo this is accomplished by merging hardened-gcc: =20

-# emerge hardened-gcc
+# emerge hardened-gcc

=20 -

hardened-gcc is an umbrella package for non-mainstream gcc = modifications - The hardened-gcc packages was initially created by Alexander G= abert=20 +

hardened-gcc is an umbrella package for non-mainstream gcc = modifications + The hardened-gcc packages was initially created by Alexander G= abert=20 for this special purpose we are serving here: rolling out the etdyn specs file and interp.o together with the position independent crt1S.o. But this package is not limited to that purpose. =20 @@ -184,21 +189,17 @@ These guidelines are required to achieve full Addre= ss Space Layout Randomization one is chpax built as an ET_EXEC.

=20

-# file /sbin/chpax
+# file /sbin/chpax
 /sbin/chpax: ELF 32-bit LSB shared object, Intel 80386, version 1 \
 (GNU/Linux), stripped
 /sbin/chpax: ELF 32-bit LSB executable, Intel 80386, version 1 (SYSV), f=
or \
 GNU/Linux 2.0.0, dynamically linked (uses shared libs), stripped

=20 - - - + =20 -To keep the bugs down for us we really dont want the -end user mucking with the specs -solar - -

We can further simplify the building of ET_DYN executables by modi= fying + + +

+ + + =20 Credits

=20