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

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Message-Id: <B974F3CA-6A2A-42EB-A478-3606BCCB520D@amacapital.net>
Date:   Fri, 5 Jan 2018 12:10:02 -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 11:28 AM, Borislav Petkov <bp@...en8.de> wrote:
> 
>> On Fri, Jan 05, 2018 at 11:22:21AM -0800, Andy Lutomirski wrote:
>> It's emulated!  We catch the page fault and fake the whole thing :)
> 
> Then I'm really confused. It says "ro" above, which means _PAGE_RW is
> not set so page is read-only.
> 
> I must be missing something...
> 

It's meant to be read-only, user-acccessible, NX as far as the CPU is concerned.  When user code calls it, we get an instruction fetch fault, and the kernel fixes it up.

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