Re: [PATCH v6 20/27] x86: Support global stack cookie

[Andy Lutomirski]

On Thu, Jan 31, 2019 at 11:29 AM Thomas Garnier <thgarnie@xxxxxxxxxxxx> wrote:
>
> Add an off-by-default configuration option to use a global stack cookie
> instead of the default TLS. This configuration option will only be used
> with PIE binaries.
>
> For kernel stack cookie, the compiler uses the mcmodel=kernel to switch
> between the fs segment to gs segment. A PIE binary does not use
> mcmodel=kernel because it can be relocated anywhere, therefore the
> compiler will default to the fs segment register. This is fixed on the
> latest version of gcc.

I hate all these gcc-sucks-so-we-hack-it-and-change-nasty-semantics
options.  How about just preventing use of both stack protector and
PIE unless the version of gcc in use is new enough.

Also, does -mstack-protector-guard-reg not solve this?  See
https://gcc.gnu.org/bugzilla/show_bug.cgi?id=81708.  Or is there
another bug?  Or are you worried about gcc versions that don't have
that feature yet?