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Date:   Thu, 16 Jun 2022 11:34:14 +0200
From:   Peter Zijlstra <peterz@infradead.org>
To:     "Edgecombe, Rick P" <rick.p.edgecombe@intel.com>
Cc:     "kirill.shutemov@linux.intel.com" <kirill.shutemov@linux.intel.com>,
        "Lutomirski, Andy" <luto@kernel.org>,
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        "linux-mm@kvack.org" <linux-mm@kvack.org>,
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        "andreyknvl@gmail.com" <andreyknvl@gmail.com>,
        "ak@linux.intel.com" <ak@linux.intel.com>,
        "dvyukov@google.com" <dvyukov@google.com>,
        "x86@kernel.org" <x86@kernel.org>,
        "ryabinin.a.a@gmail.com" <ryabinin.a.a@gmail.com>,
        "glider@google.com" <glider@google.com>
Subject: Re: [PATCHv3 5/8] x86/uaccess: Provide untagged_addr() and remove
 tags before address check
Message-ID: <Yqr5FmoBB5LZRhU5@hirez.programming.kicks-ass.net>
References: <20220610143527.22974-1-kirill.shutemov@linux.intel.com>
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On Mon, Jun 13, 2022 at 05:36:43PM +0000, Edgecombe, Rick P wrote:

> Is this special kernel address handling only needed because
> copy_to_kernel_nofault(), etc call the user helpers?

It is to make absolutely sure we don't need to go audit everything, if
code is correct without untag_pointer() it will still be correct with it
on.

Also avoids future bugs due to being robust in general.