linux-kernel - Re: [PATCH] x86: Disable CET instrumentation in the kernel

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Date:   Fri, 29 Jan 2021 11:03:31 -0600
From:   Josh Poimboeuf <jpoimboe@...hat.com>
To:     Nikolay Borisov <nborisov@...e.com>
Cc:     Borislav Petkov <bp@...en8.de>, x86@...nel.org,
        Masami Hiramatsu <masami.hiramatsu@...il.com>,
        Masami Hiramatsu <mhiramat@...nel.org>,
        Peter Zijlstra <peterz@...radead.org>,
        LKML <linux-kernel@...r.kernel.org>,
        Alexei Starovoitov <ast@...nel.org>, bpf@...r.kernel.org,
        Steven Rostedt <rostedt@...dmis.org>
Subject: Re: [PATCH] x86: Disable CET instrumentation in the kernel

On Fri, Jan 29, 2021 at 06:54:08PM +0200, Nikolay Borisov wrote:
> 
> 
> On 29.01.21 г. 18:49 ч., Josh Poimboeuf wrote:
> > Agreed, stable is a good idea.   I think Nikolay saw it with GCC 9.
> 
> 
> Yes I did, with the default Ubuntu compiler as well as the default gcc-10 compiler: 
> 
> # gcc -v -Q -O2 --help=target | grep protection
> 
> gcc version 9.3.0 (Ubuntu 9.3.0-17ubuntu1~20.04) 
> COLLECT_GCC_OPTIONS='-v' '-Q' '-O2' '--help=target' '-mtune=generic' '-march=x86-64'
>  /usr/lib/gcc/x86_64-linux-gnu/9/cc1 -v -imultiarch x86_64-linux-gnu help-dummy -dumpbase help-dummy -mtune=generic -march=x86-64 -auxbase help-dummy -O2 -version --help=target -fasynchronous-unwind-tables -fstack-protector-strong -Wformat -Wformat-security -fstack-clash-protection -fcf-protection -o /tmp/ccSecttk.s
> GNU C17 (Ubuntu 9.3.0-17ubuntu1~20.04) version 9.3.0 (x86_64-linux-gnu)
> 	compiled by GNU C version 9.3.0, GMP version 6.2.0, MPFR version 4.0.2, MPC version 1.1.0, isl version isl-0.22.1-GMP
> 
> 
> It has -fcf-protection turned on by default it seems. 

Yup, explains why I didn't see it:

gcc version 10.2.1 20201125 (Red Hat 10.2.1-9) (GCC)
COLLECT_GCC_OPTIONS='-v' '-Q' '-O2' '--help=target' '-mtune=generic' '-march=x86-64'
 /usr/libexec/gcc/x86_64-redhat-linux/10/cc1 -v help-dummy -dumpbase help-dummy -mtune=generic -march=x86-64 -auxbase help-dummy -O2 -version --help=target -o /tmp/cclBz55H.s


-- 
Josh