linux-kernel - Re: [PATCH 10/11] retpoline/taint: Taint kernel for missing retpoline in compiler

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Date:   Thu, 4 Jan 2018 01:29:58 +0100 (CET)
From:   Thomas Gleixner <tglx@...utronix.de>
To:     Andi Kleen <andi@...stfloor.org>
cc:     tglx@...uxtronix.de, torvalds@...ux-foundation.org,
        gregkh@...ux-foundation.org, dwmw@...zon.co.uk,
        tim.c.chen@...ux.intel.com, linux-kernel@...r.kernel.org,
        dave.hansen@...el.com, Andi Kleen <ak@...ux.intel.com>
Subject: Re: [PATCH 10/11] retpoline/taint: Taint kernel for missing retpoline
 in compiler

On Wed, 3 Jan 2018, Andi Kleen wrote:
>  	unwind_init();
> +
> +#ifndef RETPOLINE
> +	add_taint(TAINT_NO_RETPOLINE, LOCKDEP_STILL_OK);
> +	pr_warn("No support for retpoline in kernel compiler\n");
> +	pr_warn("Kernel may be vulnerable to data leaks.\n");

That's blantantly wrong.

The kernel is not vulnerable to data leaks. The hardware is.

An that's what the CPU_BUG bit is for. If the mitigation is in place,
activate the proper feature bit like we did with PTI

Thanks,

	tglx