linux-kernel - Re: [RFC] selftests/x86: Add test

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Date:   Fri, 5 Jan 2018 11:22:21 -0800
From:   Andy Lutomirski <luto@...capital.net>
To:     Borislav Petkov <bp@...en8.de>
Cc:     Andy Lutomirski <luto@...nel.org>, X86 ML <x86@...nel.org>,
        LKML <linux-kernel@...r.kernel.org>,
        Kees Cook <keescook@...omium.org>,
        Peter Zijlstra <peterz@...radead.org>,
        Greg Kroah-Hartman <gregkh@...uxfoundation.org>
Subject: Re: [RFC] selftests/x86: Add test_vsyscall



> On Jan 5, 2018, at 11:10 AM, Borislav Petkov <bp@...en8.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.