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Date:   Wed, 2 Sep 2020 15:32:31 +0200
From:   Christoph Hellwig <hch@lst.de>
To:     Mark Rutland <mark.rutland@arm.com>
Cc:     Christoph Hellwig <hch@lst.de>,
        Josh Poimboeuf <jpoimboe@redhat.com>, x86@kernel.org,
        linux-kernel@vger.kernel.org,
        Linus Torvalds <torvalds@linux-foundation.org>,
        Al Viro <viro@zeniv.linux.org.uk>,
        Will Deacon <will@kernel.org>,
        Dan Williams <dan.j.williams@intel.com>,
        Andrea Arcangeli <aarcange@redhat.com>,
        Waiman Long <longman@redhat.com>,
        Peter Zijlstra <peterz@infradead.org>,
        Thomas Gleixner <tglx@linutronix.de>,
        Andrew Cooper <andrew.cooper3@citrix.com>,
        Andy Lutomirski <luto@kernel.org>
Subject: Re: [PATCH] x86/uaccess: Use pointer masking to limit uaccess
 speculation
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References: <f12e7d3cecf41b2c29734ea45a393be21d4a8058.1597848273.git.jpoimboe@redhat.com> <20200901140208.GA95447@C02TD0UTHF1T.local> <20200901144641.GA28580@lst.de> <20200901145442.GC95447@C02TD0UTHF1T.local> <20200901150553.GA30034@lst.de> <20200901154629.GA882@lst.de> <20200902114348.GA1002@C02TD0UTHF1T.local>
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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.