linux-kernel - Re: [PATCH] x86/alternatives: Fix optimize

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Message-ID: <1515584201.22302.113.camel@infradead.org>
Date:   Wed, 10 Jan 2018 11:36:41 +0000
From:   David Woodhouse <dwmw2@...radead.org>
To:     Borislav Petkov <bp@...en8.de>
Cc:     Linus Torvalds <torvalds@...ux-foundation.org>,
        Andi Kleen <andi@...stfloor.org>,
        Thomas Gleixner <tglx@...utronix.de>,
        the arch/x86 maintainers <x86@...nel.org>,
        Linux Kernel Mailing List <linux-kernel@...r.kernel.org>,
        Paul Turner <pjt@...gle.com>,
        Andrew Lutomirski <luto@...nel.org>,
        Peter Zijlstra <peterz@...radead.org>,
        Tom Lendacky <thomas.lendacky@....com>,
        Tim Chen <tim.c.chen@...ux.intel.com>,
        Greg Kroah-Hartman <gregkh@...ux-foundation.org>,
        Dave Hansen <dave.hansen@...el.com>,
        Jiri Kosina <jikos@...nel.org>, Andi Kleen <ak@...ux.intel.com>
Subject: Re: [PATCH] x86/alternatives: Fix optimize_nops() checking

On Wed, 2018-01-10 at 12:28 +0100, Borislav Petkov wrote:
> From: Borislav Petkov <bp@...e.de>
> Date: Wed, 10 Jan 2018 12:14:07 +0100
> 
> We check only the first byte whether it is a NOP but if David Woodhouse
> wants to do some crazy experiments with slapping NOPs in front of the
> payload and having the actual instructions after it, this "optimized"
> test breaks. :-)

:)

Thank you.

Tested-by: David Woodhouse <dwmw@...zon.co.uk>

That fixed and understood, I shall remove the offending NOPs anyway,
because aligning instructions in the *altinstr* section is entirely
pointless as they might still not be aligned when they get copied into
place anyway.


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