linux-kernel - Re: [PATCHv15 06/17] x86/uaccess: Provide untagged_addr() and remove tags before address check

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Message-ID: <CAG_fn=XyP5hCe8y6B8KpcGbvK6YSuj_1Quq-OgszxRsZ1NXRGg@mail.gmail.com>
Date:   Thu, 9 Feb 2023 15:10:07 +0100
From:   Alexander Potapenko <glider@...gle.com>
To:     "Kirill A. Shutemov" <kirill.shutemov@...ux.intel.com>
Cc:     Dave Hansen <dave.hansen@...ux.intel.com>,
        Andy Lutomirski <luto@...nel.org>,
        Peter Zijlstra <peterz@...radead.org>, x86@...nel.org,
        Kostya Serebryany <kcc@...gle.com>,
        Andrey Ryabinin <ryabinin.a.a@...il.com>,
        Andrey Konovalov <andreyknvl@...il.com>,
        Taras Madan <tarasmadan@...gle.com>,
        Dmitry Vyukov <dvyukov@...gle.com>,
        "H . J . Lu" <hjl.tools@...il.com>,
        Andi Kleen <ak@...ux.intel.com>,
        Rick Edgecombe <rick.p.edgecombe@...el.com>,
        Bharata B Rao <bharata@....com>,
        Jacob Pan <jacob.jun.pan@...ux.intel.com>,
        Ashok Raj <ashok.raj@...el.com>,
        Linus Torvalds <torvalds@...ux-foundation.org>,
        linux-mm@...ck.org, linux-kernel@...r.kernel.org
Subject: Re: [PATCHv15 06/17] x86/uaccess: Provide untagged_addr() and remove
 tags before address check

On Mon, Jan 23, 2023 at 11:05 PM Kirill A. Shutemov
<kirill.shutemov@...ux.intel.com> wrote:
>
> untagged_addr() is a helper used by the core-mm to strip tag bits and
> get the address to the canonical shape based on rules of the current
> thread. It only handles userspace addresses.
>
> The untagging mask is stored in per-CPU variable and set on context
> switching to the task.
>
> The tags must not be included into check whether it's okay to access the
> userspace address. Strip tags in access_ok().
>
> Signed-off-by: Kirill A. Shutemov <kirill.shutemov@...ux.intel.com>
> Acked-by: Peter Zijlstra (Intel) <peterz@...radead.org>
Tested-by: Alexander Potapenko <glider@...gle.com>