linux-kernel - Re: [PATCH 17/30] x86, kaiser: map debug IDT tables

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Message-ID: <CALCETrUgi-q1S82Btjjhk7tpPim+M1QzicGu7a6hAva-tbBVzQ@mail.gmail.com>
Date:   Mon, 20 Nov 2017 12:44:35 -0800
From:   Andy Lutomirski <luto@...nel.org>
To:     Dave Hansen <dave.hansen@...ux.intel.com>
Cc:     "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, richard.fellner@...dent.tugraz.at,
        Andrew Lutomirski <luto@...nel.org>,
        Linus Torvalds <torvalds@...ux-foundation.org>,
        Kees Cook <keescook@...gle.com>,
        Hugh Dickins <hughd@...gle.com>, X86 ML <x86@...nel.org>
Subject: Re: [PATCH 17/30] x86, kaiser: map debug IDT tables

On Fri, Nov 10, 2017 at 11:31 AM, Dave Hansen
<dave.hansen@...ux.intel.com> wrote:
>
> From: Dave Hansen <dave.hansen@...ux.intel.com>
>
> The IDT is another structure which the CPU references via a
> virtual address.  It also obviously needs these to handle an
> interrupt in userspace, so these need to be mapped into the user
> copy of the page tables.

Why would the debug IDT ever be used in user mode?  IIRC it's a total
turd related to avoiding crap nesting inside NMI.  Or am I wrong?

If it *is* used in user mode, then we have a bug and it should be in
the IDT to avoid address leaks just like the normal IDT.

--Andy