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From: Linus Torvalds <torvalds@linux-foundation.org>
Date: Thu, 14 Dec 2017 14:14:00 -0800
Message-ID: <CA+55aFzT=+Vc75O8yjGYcSiWVVvrRMOZT2Ydhs7S=0RUAtscAA@mail.gmail.com>
Subject: Re: [PATCH v2 11/17] selftests/x86/ldt_gdt: Prepare for access bit forced
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To: Peter Zijlstra <peterz@infradead.org>
Cc: Andy Lutomirski <luto@kernel.org>, "linux-kernel@vger.kernel.org" <linux-kernel@vger.kernel.org>, Thomas Gleixner <tglx@linutronix.de>, X86 ML <x86@kernel.org>, Dave Hansen <dave.hansen@intel.com>, Borislav Petkov <bpetkov@suse.de>, Greg KH <gregkh@linuxfoundation.org>, Kees Cook <keescook@google.com>, Hugh Dickins <hughd@google.com>, Brian Gerst <brgerst@gmail.com>, Josh Poimboeuf <jpoimboe@redhat.com>, Denys Vlasenko <dvlasenk@redhat.com>, Boris Ostrovsky <boris.ostrovsky@oracle.com>, Juergen Gross <jgross@suse.com>, David Laight <David.Laight@aculab.com>, Eduardo Valentin <eduval@amazon.com>, "Liguori, Anthony" <aliguori@amazon.com>, Will Deacon <will.deacon@arm.com>, "linux-mm@kvack.org" <linux-mm@kvack.org>, "Kirill A. Shutemov" <kirill.shutemov@linux.intel.com>, Dan Williams <dan.j.williams@intel.com>

On Thu, Dec 14, 2017 at 2:02 PM, Peter Zijlstra <peterz@infradead.org> wrote:
>
> _Should_ being the operative word, because I cannot currently see it
> DTRT. But maybe I'm missing the obvious -- I tend to do that at times.

At least the old get_user_pages_fast() code used to check the USER bit:

        unsigned long need_pte_bits = _PAGE_PRESENT|_PAGE_USER;

        if (write)
                need_pte_bits |= _PAGE_RW;

but that may have been lost when we converted over to the generic code.

It shouldn't actually _matter_, since we'd need to change access_ok()
anyway (and gup had better check that!)

             Linus

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