Changing stack protector initialization

[Florian Weimer <fweimer@redhat.com>]

I need a few more pseudo-random bits (32 instead of 16 on 64-bit 
architectures).  I talked to some cryptography people and they told me 
to expand the 16-byte secret by hashing it with SHA-256.

This key expansion has to happen both in ld.so (for the stack protector 
and pointer guard) and libc.so (for the new stuff).  My first attempt 
failed because doing the initialization in ld.so triggers duplication of 
the new guard variables from libc.so in ld.so, and the libc.so variables 
are never initialized.  (This is very confusing to GDB, which does not 
tell you that you have two variables with the same name at different 
addresses.)

I think the best approach is to duplicate the initialization code and 
run it twice, once based on the _dl_random value, and once using 
getauxval (AT_RANDOM).  The other alternative would be to put the values 
computed by rtld into rtld_global or some similar place and use those 
values to initialize the libc.so variables, but this wastes 16 bytes in 
the data segment per process.  (I need to make a copy so that the 
variable access does not go through the GOT.)

Is there another option to implement this?

Thanks,
Florian