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Date:   Tue, 6 Oct 2020 10:26:25 +0200
From:   Peter Zijlstra <peterz@infradead.org>
To:     Andy Lutomirski <luto@kernel.org>
Cc:     x86@kernel.org, LKML <linux-kernel@vger.kernel.org>,
        "Christopherson, Sean J" <sean.j.christopherson@intel.com>
Subject: Re: [PATCH 1/2] x86/stackprotector/32: Make the canary into a
 regular percpu variable
Message-ID: <20201006082625.GM2628@hirez.programming.kicks-ass.net>
References: <cover.1601925251.git.luto@kernel.org>
 <4b3b4fbf8e9806840135e95cef142a0adefc3455.1601925251.git.luto@kernel.org>
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On Mon, Oct 05, 2020 at 12:30:03PM -0700, Andy Lutomirski wrote:
> @@ -441,6 +441,9 @@ struct fixed_percpu_data {
>  	 * GCC hardcodes the stack canary as %gs:40.  Since the
>  	 * irq_stack is the object at %gs:0, we reserve the bottom
>  	 * 48 bytes of the irq stack for the canary.
> +	 *
> +	 * Once we are willing to require -mstack-protector-guard-symbol=
> +	 * support for x86_64 stackprotector, we can get rid of this.
>  	 */
>  	char		gs_base[40];
>  	unsigned long	stack_canary;

I'm all in favour of simply requiring GCC-8.1 to build a more secure
x86_64 kernel. Gives people an incentive to not use ancient compilers.

And if you do want to use your ancient compiler, we'll still build, you
just don't get to have stackprotector.