linux-kernel - Re: [PATCH 06/18] x86, barrier: stop speculation for failed access

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Date:   Sat, 6 Jan 2018 22:21:04 +0100 (CET)
From:   Thomas Gleixner <tglx@...utronix.de>
To:     Alexei Starovoitov <alexei.starovoitov@...il.com>
cc:     Alan Cox <gnomes@...rguk.ukuu.org.uk>,
        Linus Torvalds <torvalds@...ux-foundation.org>,
        Dan Williams <dan.j.williams@...el.com>,
        linux-kernel@...r.kernel.org, linux-arch@...r.kernel.org,
        Andi Kleen <ak@...ux.intel.com>, Arnd Bergmann <arnd@...db.de>,
        Greg Kroah-Hartman <gregkh@...uxfoundation.org>,
        Peter Zijlstra <peterz@...radead.org>, netdev@...r.kernel.org,
        Ingo Molnar <mingo@...hat.com>,
        "H. Peter Anvin" <hpa@...or.com>
Subject: Re: [PATCH 06/18] x86, barrier: stop speculation for failed
 access_ok

On Sat, 6 Jan 2018, Alexei Starovoitov wrote:
> So how about we do array_access() macro similar to above by default
> with extra CONFIG_ to convert it to lfence ?
> Why default to AND approach instead of lfence ?
> Because the kernel should still be usable. If security
> sacrifices performance so much such security will be turned off.
> Ex: kpti suppose to add 5-30%. If it means 10% on production workload
> and the datacenter capacity cannot grow 10% overnight, kpti will be off.

That's the decision and responsibility of the person who disables it.

Thanks,

	tglx