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From:   Kees Cook <keescook@google.com>
Date:   Mon, 23 Apr 2018 10:06:20 -0700
Message-ID: <CAGXu5jLN_rzmfgM-Xne836ip+qMc8T1QX=mhozo3NFLNssgUfw@mail.gmail.com>
Subject: Re: [PATCH 27/37] x86/mm/pti: Keep permissions when cloning kernel
 text in pti_clone_kernel_text()
To:     Joerg Roedel <joro@8bytes.org>
Cc:     Thomas Gleixner <tglx@linutronix.de>,
        Ingo Molnar <mingo@kernel.org>,
        "H . Peter Anvin" <hpa@zytor.com>, X86 ML <x86@kernel.org>,
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        Linus Torvalds <torvalds@linux-foundation.org>,
        Andy Lutomirski <luto@kernel.org>,
        Dave Hansen <dave.hansen@intel.com>,
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        Brian Gerst <brgerst@gmail.com>,
        David Laight <David.Laight@aculab.com>,
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        Daniel Gruss <daniel.gruss@iaik.tugraz.at>,
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        Andrea Arcangeli <aarcange@redhat.com>,
        Waiman Long <llong@redhat.com>, Pavel Machek <pavel@ucw.cz>,
        "David H . Gutteridge" <dhgutteridge@sympatico.ca>,
        Joerg Roedel <jroedel@suse.de>
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On Mon, Apr 23, 2018 at 8:47 AM, Joerg Roedel <joro@8bytes.org> wrote:
> From: Joerg Roedel <jroedel@suse.de>
>
> Mapping the kernel text area to user-space makes only sense
> if it has the same permissions as in the kernel page-table.
> If permissions are different this will cause a TLB reload
> when using the kernel page-table, which is as good as not
> mapping it at all.
>
> On 64-bit kernels this patch makes no difference, as the
> whole range cloned by pti_clone_kernel_text() is mapped RO
> anyway. On 32 bit there are writeable mappings in the range,
> so just keep the permissions as they are.

Why are there R/W text mappings in this range? I find that to be
unexpected. Shouldn't CONFIG_DEBUG_WX already complain if that were
true?

-Kees

-- 
Kees Cook
Pixel Security