linux-kernel - Re: [PATCHv5 05/13] x86/uaccess: Provide untagged_addr() and remove tags before address check

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Date:   Thu, 21 Jul 2022 15:14:19 +0200
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>,
        "the arch/x86 maintainers" <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>,
        Linux Memory Management List <linux-mm@...ck.org>,
        LKML <linux-kernel@...r.kernel.org>
Subject: Re: [PATCHv5 05/13] x86/uaccess: Provide untagged_addr() and remove
 tags before address check

On Wed, Jul 13, 2022 at 1:13 AM 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. In only handles userspace
> addresses. The untagging mask is stored in mmu_context and will be set
> on enabling LAM for the process.
>
> The tags must not be included into check whether it's okay to access the
> userspace address.
>
> Strip tags in access_ok().
>
> get_user() and put_user() don't use access_ok(), but check access
> against TASK_SIZE directly in assembly. Strip tags, before calling into
> the assembly helper.
>
> Signed-off-by: Kirill A. Shutemov <kirill.shutemov@...ux.intel.com>
Tested-by: Alexander Potapenko <glider@...gle.com>