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Subject: Re: [RFC] selftests/x86: Add test_vsyscall
From: Andy Lutomirski <luto@amacapital.net>
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Date: Fri, 5 Jan 2018 11:22:21 -0800
Cc: Andy Lutomirski <luto@kernel.org>, X86 ML <x86@kernel.org>,
        LKML <linux-kernel@vger.kernel.org>,
        Kees Cook <keescook@chromium.org>,
        Peter Zijlstra <peterz@infradead.org>,
        Greg Kroah-Hartman <gregkh@linuxfoundation.org>
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References: <17c5ebeb2e00879b0af1a9c32bf37ecdd9b9b31b.1515130397.git.luto@kernel.org> <20180105134025.kzmnydmzrnfdokz7@pd.tnic> <CALCETrVp3AaiXcZrxKCw0ABdn5_HjO8Ud0BcapGxABRyB=sFdA@mail.gmail.com> <20180105183048.ywi5cccs4ecggwy3@pd.tnic> <CALCETrVyXAup_9uZb5EU6CWeX3TQfA6DQV9KzVbfa3b5g9zzdA@mail.gmail.com> <20180105191000.n2gnkbsyry4kd65z@pd.tnic>
To: Borislav Petkov <bp@alien8.de>
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> On Jan 5, 2018, at 11:10 AM, Borislav Petkov <bp@alien8.de> wrote:
> 
>> On Fri, Jan 05, 2018 at 10:45:49AM -0800, Andy Lutomirski wrote:
>> Not _PAGE_RW.  Probably _PAGE_USER somewhere in the hierarchy.
> 
> Yeah, just realized that. But it must be somewhere in the PT hierarchy
> because:
> 
> 0xffffffffff600000-0xffffffffff601000           4K USR ro                     NX pte
> 
> So something up needs to take _PAGE_USER too.
> 
> But WTF does it say NX there for and still can execute the vsyscall
> test? Oh boy, what a mess...
> 

It's emulated!  We catch the page fault and fake the whole thing :)

> -- 
> Regards/Gruss,
>    Boris.
> 
> Good mailing practices for 400: avoid top-posting and trim the reply.