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

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Date:   Wed, 10 Apr 2019 13:42:59 +0200
From:   Ingo Molnar <mingo@...nel.org>
To:     Elena Reshetova <elena.reshetova@...el.com>,
        Andy Lutomirski <luto@...nel.org>
Cc:     luto@...nel.org, linux-kernel@...r.kernel.org, luto@...capital.net,
        jpoimboe@...hat.com, keescook@...omium.org, jannh@...gle.com,
        enrico.perla@...el.com, mingo@...hat.com, bp@...en8.de,
        tglx@...utronix.de, peterz@...radead.org,
        gregkh@...uxfoundation.org
Subject: Re: [PATCH 1/1] x86/entry/64: randomize kernel stack offset upon
 syscall


* Elena Reshetova <elena.reshetova@...el.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'm using cb7f9f0592f8, which is like 1.5 years old - is this still the 
latest and greatest:

  git://git.kernel.org/pub/scm/linux/kernel/git/luto/misc-tests.git

?

Thanks,

	Ingo