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References: <cover.1464129798.git.luto@kernel.org> <f766e3c623fd9cf76568741e28e28d0de7d912ce.1464129798.git.luto@kernel.org>
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From: Andy Lutomirski <luto@amacapital.net>
Date: Sun, 29 May 2016 09:52:26 -0700
Message-ID: <CALCETrXRu2hZgZgQhzSv_Xf3CVKfM4hAg0rA5g=KDTG9wedbsw@mail.gmail.com>
Subject: Re: [PATCH 7/7] x86/uaccess: OOPS or warn on a fault with KERNEL_DS
 and !pagefault_disabled()
To: Borislav Petkov <bp@alien8.de>
Cc: Andy Lutomirski <luto@kernel.org>, X86 ML <x86@kernel.org>,
        "linux-kernel@vger.kernel.org" <linux-kernel@vger.kernel.org>,
        Kees Cook <keescook@chromium.org>, Brian Gerst <brgerst@gmail.com>
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On Wed, May 25, 2016 at 8:33 AM, Borislav Petkov <bp@alien8.de> wrote:
> On Tue, May 24, 2016 at 03:48:44PM -0700, Andy Lutomirski wrote:
>> +     if (unlikely(!is_user_ds && !pagefault_disabled())) {
>> +             if (extra < TASK_SIZE_MAX) {
>> +                     /*
>> +                      * Accessing user address under KERNEL_DS.  This is a
>> +                      * bug and should be fixed, but OOPSing is not helpful
>> +                      * for exploit mitigation.
>> +                      */
>> +                     WARN_ONCE(1, "BUG: uaccess fault at 0x%lx with KERNEL_DS\n",
>
>                         WARN and BUG?
>
> Also, let's have this string and the one below differ for finding out
> where we are during debugging.

Done.