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From: Dave Hansen <dave.hansen@linux.intel.com>
To: Andy Lutomirski <luto@kernel.org>
Cc: "linux-kernel@vger.kernel.org" <linux-kernel@vger.kernel.org>,
	"linux-mm@kvack.org" <linux-mm@kvack.org>,
	richard.fellner@student.tugraz.at, moritz.lipp@iaik.tugraz.at,
	Daniel Gruss <daniel.gruss@iaik.tugraz.at>,
	michael.schwarz@iaik.tugraz.at,
	Linus Torvalds <torvalds@linux-foundation.org>,
	Kees Cook <keescook@google.com>, Hugh Dickins <hughd@google.com>,
	X86 ML <x86@kernel.org>
Subject: Re: [PATCH 05/23] x86, kaiser: unmap kernel from userspace page tables (core patch)
Date: Sun, 26 Nov 2017 08:24:37 -0800	[thread overview]
Message-ID: <2e4773b2-2cb3-284e-f0a7-3eaebc2676e5@linux.intel.com> (raw)
In-Reply-To: <CALCETrXqcB_2oBktvLTc2k1z_O65mTs2rDF5ZMYnFvhs2Kh3Ng@mail.gmail.com>

On 11/26/2017 08:10 AM, Andy Lutomirski wrote:
>> As a side benefit, this shouldn't have magical interactions with the
>> vsyscall page any more.
>>
>> Are there cases that this would get wrong?
>>
> Quick ping: did this get lost?

It does drop a warning that the other version of the code has, but
that's pretty minor.

Basically, we need two checks:

	pgd_userspace_access() (aka _PAGE_USER) and
	pgdp_maps_userspace()

The original code does pgd_userspace_access() in a top-level if and then
the pgdp_maps_userspace() checks at the second level.  I think you are
basically suggesting that we flip that.

Logically, I'm sure we can make it work.  It's just a matter of needing
to look at other things first.

BTW, this comment is, I think incorrect:

>   if (pgdp_maps_userspace(pgdp)) {
...
>   } else {
>     /*
>      * We can get here due to vmalloc, a vmalloc fault, memory
> hot-add, or initial setup
>      * of kernelmode page tables.  Regardless of which particular code
> path we're in,
>      * these mappings should not be automatically propagated to the
> usermode tables.
>      */

Since we pre-populated the entire kernel area's PGDs, I don't think
we'll ever have a valid reason to be doing a set_pgd() again on the
kernel area.

  reply	other threads:[~2017-11-26 16:24 UTC|newest]

Thread overview: 66+ messages / expand[flat|nested]  mbox.gz  Atom feed  top
2017-11-23  0:34 [PATCH 00/23] [v4] KAISER: unmap most of the kernel from userspace page tables Dave Hansen
2017-11-23  0:34 ` [PATCH 01/23] x86, kaiser: disable global pages by default with KAISER Dave Hansen
2017-11-23  0:34 ` [PATCH 02/23] x86, kaiser: prepare assembly for entry/exit CR3 switching Dave Hansen
2017-11-23  0:34 ` [PATCH 03/23] x86, kaiser: introduce user-mapped per-cpu areas Dave Hansen
2017-11-23  0:34 ` [PATCH 04/23] x86, kaiser: mark per-cpu data structures required for entry/exit Dave Hansen
2017-11-23  0:34 ` [PATCH 05/23] x86, kaiser: unmap kernel from userspace page tables (core patch) Dave Hansen
2017-11-23  4:07   ` Andy Lutomirski
2017-11-26 16:10     ` Andy Lutomirski
2017-11-26 16:24       ` Dave Hansen [this message]
2017-11-26 16:29         ` Andy Lutomirski
2018-01-05  4:16   ` Yisheng Xie
2018-01-05  5:18     ` Dave Hansen
2018-01-05  6:16       ` Yisheng Xie
2018-01-05  6:29         ` Dave Hansen
2018-01-05 11:49           ` Andrea Arcangeli
2018-01-05 18:19           ` Jiri Kosina
2018-01-05 19:00             ` Jiri Kosina
2018-01-05 19:03             ` Dave Hansen
2018-01-05 19:17               ` Jiri Kosina
2018-01-05 19:18                 ` Jiri Kosina
2018-01-05 19:55                 ` Andrea Arcangeli
2018-01-05 21:07                 ` Dave Hansen
2018-01-05 21:14                   ` Jiri Kosina
2018-01-05 21:29                     ` Andy Lutomirski
2018-01-05 22:48                     ` Hugh Dickins
2018-01-06  4:54             ` Hanjun Guo
2018-01-06  6:06               ` Dave Hansen
2018-01-06  6:28                 ` Hanjun Guo
2018-01-06  6:53                   ` Hanjun Guo
2018-01-06  7:55                     ` Dave Hansen
2018-01-06  8:42                       ` Hanjun Guo
2018-01-06  7:51                   ` Dave Hansen
2018-01-06 17:22                     ` Andrea Arcangeli
2017-11-23  0:34 ` [PATCH 06/23] x86, kaiser: allow NX poison to be set in p4d/pgd Dave Hansen
2017-11-23  0:34 ` [PATCH 07/23] x86, kaiser: make sure static PGDs are 8k in size Dave Hansen
2017-11-23  0:34 ` [PATCH 08/23] x86, kaiser: map cpu entry area Dave Hansen
2017-11-23  0:34 ` [PATCH 09/23] x86, kaiser: map dynamically-allocated LDTs Dave Hansen
2017-11-23 19:42   ` Eric Biggers
2017-11-23 20:12     ` Andy Lutomirski
2017-11-23  0:34 ` [PATCH 10/23] x86, kaiser: map espfix structures Dave Hansen
2017-11-23  0:34 ` [PATCH 11/23] x86, kaiser: map entry stack variables Dave Hansen
2017-11-23  3:31   ` Andy Lutomirski
2017-11-23 15:37     ` Dave Hansen
2017-11-23 15:55       ` Andy Lutomirski
2017-11-23  0:35 ` [PATCH 12/23] x86, kaiser: map virtually-addressed performance monitoring buffers Dave Hansen
2017-11-23  0:35 ` [PATCH 13/23] x86, mm: Move CR3 construction functions Dave Hansen
2017-11-23  0:35 ` [PATCH 14/23] x86, mm: remove hard-coded ASID limit checks Dave Hansen
2017-11-23  0:35 ` [PATCH 15/23] x86, mm: put mmu-to-h/w ASID translation in one place Dave Hansen
2017-11-23  0:35 ` [PATCH 16/23] x86, pcid, kaiser: allow flushing for future ASID switches Dave Hansen
2017-11-23  0:35 ` [PATCH 17/23] x86, kaiser: use PCID feature to make user and kernel switches faster Dave Hansen
2017-11-23  0:35 ` [PATCH 18/23] x86, kaiser: disable native VSYSCALL Dave Hansen
2017-11-23  0:35 ` [PATCH 19/23] x86, kaiser: add debugfs file to turn KAISER on/off at runtime Dave Hansen
2017-11-23  0:35 ` [PATCH 20/23] x86, kaiser: add a function to check for KAISER being enabled Dave Hansen
2017-11-25  1:23   ` Eduardo Valentin
2017-11-23  0:35 ` [PATCH 21/23] x86, kaiser: un-poison PGDs at runtime Dave Hansen
2017-11-25  1:17   ` Eduardo Valentin
2017-11-23  0:35 ` [PATCH 22/23] x86, kaiser: allow KAISER to be enabled/disabled " Dave Hansen
2017-11-23  0:35 ` [PATCH 23/23] x86, kaiser: add Kconfig Dave Hansen
2017-11-23  7:23 ` [PATCH 00/23] [v4] KAISER: unmap most of the kernel from userspace page tables Ingo Molnar
2017-11-23  7:27 ` Ingo Molnar
2017-11-23  7:32   ` Ingo Molnar
2017-11-23 15:02     ` Dave Hansen
2017-11-23 16:20 ` Dave Hansen
2017-11-24  6:35   ` Ingo Molnar
2017-11-24  6:41     ` Dave Hansen
2017-11-24  7:33       ` Ingo Molnar

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