linux-kernel - Re: [tip:x86/urgent] x86/io: Mark target address as output in 'insb()' asm

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Message-ID: <20170712192421.cpuucr2a233xcovl@gmail.com>
Date:   Wed, 12 Jul 2017 21:24:22 +0200
From:   Ingo Molnar <mingo@...nel.org>
To:     Linus Torvalds <torvalds@...ux-foundation.org>
Cc:     Andrew Lutomirski <luto@...nel.org>,
        Denys Vlasenko <dvlasenk@...hat.com>,
        Borislav Petkov <bp@...en8.de>,
        Josh Poimboeuf <jpoimboe@...hat.com>,
        Kalle Valo <kvalo@...eaurora.org>, Peter Anvin <hpa@...or.com>,
        Linux Kernel Mailing List <linux-kernel@...r.kernel.org>,
        Thomas Gleixner <tglx@...utronix.de>,
        Arnd Bergmann <arnd@...db.de>,
        Peter Zijlstra <peterz@...radead.org>,
        Brian Gerst <brgerst@...il.com>,
        "linux-tip-commits@...r.kernel.org" 
        <linux-tip-commits@...r.kernel.org>
Subject: Re: [tip:x86/urgent] x86/io: Mark target address as output in
 'insb()' asm


* Linus Torvalds <torvalds@...ux-foundation.org> wrote:

> On Wed, Jul 12, 2017 at 6:10 AM, tip-bot for Arnd Bergmann
> <tipbot@...or.com> wrote:
> >
> > Apparently the assember constraints are slightly off here, as marking the
> > 'addr' argument as a memory output seems appropriate here and gets rid
> > of the warning. For consistency I'm also adding it as input for outsb().
> 
> The new constraints look very questionable to me.

Ok, I've removed the commit.

> The real fix is probably to just mark them as "clobbers memory" (ie
> just add "memory" to the clobber list).
> 
> If you want to be fancy, you can try to do what <asm/uaccess.h> does,
> which is a disgusting hack, but has traditionally worked;
> 
>   struct __large_struct { unsigned long buf[100]; };
>   #define __m(x) (*(struct __large_struct __user *)(x))
> 
> and then use your approach with "m" and "=m".

Arnd, could you please try Linus's suggestions?

Thanks,

	Ingo