linux-kernel - Re: [PATCH] x86/uaccess: Use pointer masking to limit uaccess speculation

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Message-ID: <20200902133231.GA32133@lst.de>
Date:   Wed, 2 Sep 2020 15:32:31 +0200
From:   Christoph Hellwig <hch@....de>
To:     Mark Rutland <mark.rutland@....com>
Cc:     Christoph Hellwig <hch@....de>,
        Josh Poimboeuf <jpoimboe@...hat.com>, x86@...nel.org,
        linux-kernel@...r.kernel.org,
        Linus Torvalds <torvalds@...ux-foundation.org>,
        Al Viro <viro@...iv.linux.org.uk>,
        Will Deacon <will@...nel.org>,
        Dan Williams <dan.j.williams@...el.com>,
        Andrea Arcangeli <aarcange@...hat.com>,
        Waiman Long <longman@...hat.com>,
        Peter Zijlstra <peterz@...radead.org>,
        Thomas Gleixner <tglx@...utronix.de>,
        Andrew Cooper <andrew.cooper3@...rix.com>,
        Andy Lutomirski <luto@...nel.org>
Subject: Re: [PATCH] x86/uaccess: Use pointer masking to limit uaccess
 speculation

On Wed, Sep 02, 2020 at 12:43:48PM +0100, Mark Rutland wrote:
> I'll see what I can do.
> 
> At first glance it looks like we might need to flesh out or refactor the
> arm64 kernel maccess routines first (since we want the user maccess
> routines to use LDTR/STTR instructions that can't access kernel memory),
> but after that I think the rest is largely mechanical.

Yes, the first thing is to implement __get_kernel_nofaul and
__put_kernel_nofault.  I think they should mostly look like the existing
non-UAO versions of get_user and put_user with a fixed address space
limit.