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

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Date:   Thu, 2 Nov 2017 11:57:33 -0700
From:   Linus Torvalds <torvalds@...ux-foundation.org>
To:     Thomas Gleixner <tglx@...utronix.de>
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, 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.

              Linus