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:

quoted

On Fri, Jan 29, 2021 at 06:54:08PM +0200, Nikolay Borisov wrote:

quoted

On 29.01.21 г. 18:49 ч., Josh Poimboeuf wrote:

quoted

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 <redacted>