linux-kernel - Re: [PATCH 02/23] x86, kaiser: do not set _PAGE_USER for init

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Message-ID: <alpine.DEB.2.20.1711022233360.2824@nanos>
Date:   Thu, 2 Nov 2017 22:41:35 +0100 (CET)
From:   Thomas Gleixner <tglx@...utronix.de>
To:     Linus Torvalds <torvalds@...ux-foundation.org>
cc:     Andy Lutomirski <luto@...capital.net>,
        Dave Hansen <dave.hansen@...ux.intel.com>,
        Andy Lutomirski <luto@...nel.org>,
        "linux-kernel@...r.kernel.org" <linux-kernel@...r.kernel.org>,
        "linux-mm@...ck.org" <linux-mm@...ck.org>,
        moritz.lipp@...k.tugraz.at,
        Daniel Gruss <daniel.gruss@...k.tugraz.at>,
        michael.schwarz@...k.tugraz.at, Kees Cook <keescook@...gle.com>,
        Hugh Dickins <hughd@...gle.com>, X86 ML <x86@...nel.org>
Subject: Re: [PATCH 02/23] x86, kaiser: do not set _PAGE_USER for init_mm
 page tables


On Thu, 2 Nov 2017, Linus Torvalds wrote:

> On Thu, Nov 2, 2017 at 11:40 AM, Thomas Gleixner <tglx@...utronix.de> wrote:
> >
> > Hmm. Not sure. IIRC you need to be able to read it to figure out where the
> > entry points are. They are at fixed offsets, but there is some voodoo out
> > there which reads the 'elf' to get to them.
> 
> That would actually be really painful.
> 
> But I *think* you're confusing it with the vdso case, which really
> does do that whole "generate ELF information for debuggers and dynamic
> linkers" thing. The vsyscall page never did that afaik, and purely
> relied on fixed addresses.

Yes, managed to confuse myself. The vsycall page has only the fixed offset
entry points at least when its in emulation mode.

Thanks,

	tglx