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In-Reply-To: <20171110193138.1185728D@viggo.jf.intel.com>
References: <20171110193058.BECA7D88@viggo.jf.intel.com> <20171110193138.1185728D@viggo.jf.intel.com>
From: Andy Lutomirski <luto@kernel.org>
Date: Mon, 20 Nov 2017 12:44:35 -0800
Message-ID: <CALCETrUgi-q1S82Btjjhk7tpPim+M1QzicGu7a6hAva-tbBVzQ@mail.gmail.com>
Subject: Re: [PATCH 17/30] x86, kaiser: map debug IDT tables
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To: Dave Hansen <dave.hansen@linux.intel.com>
Cc: "linux-kernel@vger.kernel.org" <linux-kernel@vger.kernel.org>, "linux-mm@kvack.org" <linux-mm@kvack.org>, moritz.lipp@iaik.tugraz.at, Daniel Gruss <daniel.gruss@iaik.tugraz.at>, michael.schwarz@iaik.tugraz.at, richard.fellner@student.tugraz.at, Andrew Lutomirski <luto@kernel.org>, Linus Torvalds <torvalds@linux-foundation.org>, Kees Cook <keescook@google.com>, Hugh Dickins <hughd@google.com>, X86 ML <x86@kernel.org>

On Fri, Nov 10, 2017 at 11:31 AM, Dave Hansen
<dave.hansen@linux.intel.com> wrote:
>
> From: Dave Hansen <dave.hansen@linux.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

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