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Date:   Fri, 29 Jan 2021 11:58:47 -0600
From:   Seth Forshee <seth.forshee@canonical.com>
To:     Borislav Petkov <bp@alien8.de>
Cc:     Josh Poimboeuf <jpoimboe@redhat.com>,
        Nikolay Borisov <nborisov@suse.com>, x86@kernel.org,
        Masami Hiramatsu <masami.hiramatsu@gmail.com>,
        Masami Hiramatsu <mhiramat@kernel.org>,
        Peter Zijlstra <peterz@infradead.org>,
        LKML <linux-kernel@vger.kernel.org>,
        Alexei Starovoitov <ast@kernel.org>, bpf@vger.kernel.org,
        Steven Rostedt <rostedt@goodmis.org>
Subject: Re: [PATCH] x86: Disable CET instrumentation in the kernel
Message-ID: <YBRM181kNGBVKU4V@ubuntu-x1>
References: <eb1ec6a3-9e11-c769-84a4-228f23dc5e23@suse.com>
 <20210128165014.xc77qtun6fl2qfun@treble>
 <20210128215219.6kct3h2eiustncws@treble>
 <20210129102105.GA27841@zn.tnic>
 <20210129151034.iba4eaa2fuxsipqa@treble>
 <20210129163048.GD27841@zn.tnic>
 <20210129164932.qt7hhmb7x4ehomfr@treble>
 <fd874f37-5842-93ab-6b6b-872f028f2583@suse.com>
 <20210129170331.akmpnaqlwtfy4y6o@treble>
 <20210129170755.GF27841@zn.tnic>
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On Fri, Jan 29, 2021 at 06:07:55PM +0100, Borislav Petkov wrote:
> On Fri, Jan 29, 2021 at 11:03:31AM -0600, Josh Poimboeuf wrote:
> > 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
> 
> The fact that you triggered it with an Ubuntu gcc explains why the
> original patch adding that switch:
> 
> 29be86d7f9cb ("kbuild: add -fcf-protection=none when using retpoline flags")
> 
> came from a Canonical.
> 
> Adding the author to Cc for FYI.
> 
> Seth, you can find this thread starting here:
> 
> https://lkml.kernel.org/r/20210128215219.6kct3h2eiustncws@treble

Thanks for the heads up. This still works fine for our needs.

Acked-by: Seth Forshee <seth.forshee@canonical.com>