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References: <20230123220500.21077-1-kirill.shutemov@linux.intel.com> <20230123220500.21077-7-kirill.shutemov@linux.intel.com>
In-Reply-To: <20230123220500.21077-7-kirill.shutemov@linux.intel.com>
From:   Alexander Potapenko <glider@google.com>
Date:   Thu, 9 Feb 2023 15:10:07 +0100
Message-ID: <CAG_fn=XyP5hCe8y6B8KpcGbvK6YSuj_1Quq-OgszxRsZ1NXRGg@mail.gmail.com>
Subject: Re: [PATCHv15 06/17] x86/uaccess: Provide untagged_addr() and remove
 tags before address check
To:     "Kirill A. Shutemov" <kirill.shutemov@linux.intel.com>
Cc:     Dave Hansen <dave.hansen@linux.intel.com>,
        Andy Lutomirski <luto@kernel.org>,
        Peter Zijlstra <peterz@infradead.org>, x86@kernel.org,
        Kostya Serebryany <kcc@google.com>,
        Andrey Ryabinin <ryabinin.a.a@gmail.com>,
        Andrey Konovalov <andreyknvl@gmail.com>,
        Taras Madan <tarasmadan@google.com>,
        Dmitry Vyukov <dvyukov@google.com>,
        "H . J . Lu" <hjl.tools@gmail.com>,
        Andi Kleen <ak@linux.intel.com>,
        Rick Edgecombe <rick.p.edgecombe@intel.com>,
        Bharata B Rao <bharata@amd.com>,
        Jacob Pan <jacob.jun.pan@linux.intel.com>,
        Ashok Raj <ashok.raj@intel.com>,
        Linus Torvalds <torvalds@linux-foundation.org>,
        linux-mm@kvack.org, linux-kernel@vger.kernel.org
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On Mon, Jan 23, 2023 at 11:05 PM Kirill A. Shutemov
<kirill.shutemov@linux.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@linux.intel.com>
> Acked-by: Peter Zijlstra (Intel) <peterz@infradead.org>
Tested-by: Alexander Potapenko <glider@google.com>