Re: [PATCH 1/1] x86/entry/64: randomize kernel stack offset upon syscall

[Ingo Molnar <mingo@kernel.org>]

* Andy Lutomirski <luto@kernel.org> wrote:

> On Wed, Apr 10, 2019 at 4:43 AM Ingo Molnar <mingo@kernel.org> wrote:
> >
> >
> > * Elena Reshetova <elena.reshetova@intel.com> wrote:
> >
> > > 2)  Andy's tests, misc-tests: ./timing_test_64 10M sys_enosys
> > >     base:                                        10000000 loops in 1.62224s = 162.22 nsec / loop
> > >     random_offset (prandom_u32() every syscall): 10000000 loops in 1.64660s = 166.26 nsec / loop
> >
> > Stupid question, how did you manage to buil timing_test_64? Here it fails
> > with a bog standard gcc 7.3.0 x86-64 distro toolchain:
> >
> >  dagon:~/luto-misc-tests.git> make timing_test_64
> >  g++ -m64 -o timing_test_64 -O2 -g -std=gnu++11 -pthread -Wall  timing_test.cc -lrt -ldl
> >  /usr/bin/ld: /tmp/cc8VRkuV.o: relocation R_X86_64_32S against `.text.startup' can not be used when making a PIE object; recompile with -fPIC
> >  /usr/bin/ld: final link failed: Nonrepresentable section on outputcollect2: error: ld returned 1 exit status
> >  Makefile:39: recipe for target 'timing_test_64' failed
> >
> 
> I think your toolchain is screwy.  If I create this file as ingo.c:
> 
> #include <stdio.h>
> 
> int main(int argc, char **argv)
> {
>     printf("Hello world!");
> 
>     return 0;
> }
> 
> And build it like this, it fails:
> 
> $ gcc -o ingo -g ingo.c -pie
> /usr/bin/ld: /tmp/ccofYU9N.o: relocation R_X86_64_32 against `.rodata'
> can not be used when making a PIE object; recompile with -fPIC
> /usr/bin/ld: final link failed: nonrepresentable section on output
> collect2: error: ld returned 1 exit status
> 
> Which I assume means that -pie requires -fPIC, and your toolchain is
> screwed up and is defaulting to useless options.  I'm guessing you
> should file a bug against your distro gcc package.  For me, it works
> if I remove -pie.

It's just a bog standard Ubuntu x86-64 installation.

Thanks,

	Ingo