linux-kernel - RE: [PATCH 10/10] powerpc: remove address space overrides using set

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Date:   Wed, 2 Sep 2020 13:13:22 +0000
From:   David Laight <David.Laight@...LAB.COM>
To:     'Christoph Hellwig' <hch@....de>,
        Christophe Leroy <christophe.leroy@...roup.eu>
CC:     Linus Torvalds <torvalds@...ux-foundation.org>,
        Al Viro <viro@...iv.linux.org.uk>,
        Michael Ellerman <mpe@...erman.id.au>,
        "x86@...nel.org" <x86@...nel.org>,
        "linux-fsdevel@...r.kernel.org" <linux-fsdevel@...r.kernel.org>,
        "linux-arch@...r.kernel.org" <linux-arch@...r.kernel.org>,
        "linuxppc-dev@...ts.ozlabs.org" <linuxppc-dev@...ts.ozlabs.org>,
        Kees Cook <keescook@...omium.org>,
        "linux-kernel@...r.kernel.org" <linux-kernel@...r.kernel.org>
Subject: RE: [PATCH 10/10] powerpc: remove address space overrides using
 set_fs()

From: Christoph Hellwig
> Sent: 02 September 2020 13:37
> 
> On Wed, Sep 02, 2020 at 08:15:12AM +0200, Christophe Leroy wrote:
> >> -		return 0;
> >> -	return (size == 0 || size - 1 <= seg.seg - addr);
> >> +	if (addr >= TASK_SIZE_MAX)
> >> +		return false;
> >> +	if (size == 0)
> >> +		return false;
> >
> > __access_ok() was returning true when size == 0 up to now. Any reason to
> > return false now ?
> 
> No, this is accidental and broken.  Can you re-run your benchmark with
> this fixed?

Is TASK_SIZE_MASK defined such that you can do:

	return (addr | size) < TASK_SIZE_MAX) || !size;

    David

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