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From: Sebastian Andrzej Siewior <bigeasy@linutronix.de>
To: Andy Lutomirski <luto@amacapital.net>
Cc: Andy Lutomirski <luto@kernel.org>,
	Dave Hansen <dave.hansen@linux.intel.com>,
	LKML <linux-kernel@vger.kernel.org>, X86 ML <x86@kernel.org>,
	Paolo Bonzini <pbonzini@redhat.com>,
	Radim Krcmar <rkrcmar@redhat.com>, kvm list <kvm@vger.kernel.org>,
	"Jason A. Donenfeld" <Jason@zx2c4.com>,
	Rik van Riel <riel@surriel.com>
Subject: Re: [PATCH 05/11] x86/fpu: set PKRU state for kernel threads
Date: Thu, 18 Oct 2018 20:25:39 +0200	[thread overview]
Message-ID: <20181018182538.vgotfpsdy7qxl2tg@linutronix.de> (raw)
In-Reply-To: <CC7B46F7-7A6E-4CAF-A1EB-91271CC7B092@amacapital.net>

On 2018-10-18 09:48:24 [-0700], Andy Lutomirski wrote:
> > On Oct 18, 2018, at 9:26 AM, Sebastian Andrzej Siewior <bigeasy@linutronix.de> wrote:
> >> On 2018-10-12 11:02:18 [-0700], Andy Lutomirski wrote:
> >> On Fri, Oct 12, 2018 at 10:54 AM Dave Hansen
> >>> So I'm kinda missing the point of the patch.
> >> 
> >> use_mm().
> > 
> > So. I would drop that patch from queue. Anyone feels different about it?
> > 
> 
> I think we *do* want the patch. It’s a bugfix for use_mm users, right?

This is the loophole that has been pointed out. I am not convinced what
the correct behaviour should be here (and we have five users of that
interface). For instance f_fs[0].  It reads data from the USB EP and
then writes it to userland task. Due to $circumstances it happens in a
workqueue instead of the task's context.  So it borrows the mm with
use_mm().  The current behaviour random because the PKRU value can not
be predicted. It may or may not work.

Setting it to allow-all/none would let the operation always fail or
succeed which might be an improvement in terms of debugging. However it
is hard to judge what the correct behaviour should be. Should fail or
succeed.
But this is not the only loophole: There is ptrace interface which is
used by gdb (just checked) and also bypasses PKRU. So…

[0] drivers/usb/gadget/function/f_fs.c::ffs_user_copy_worker()

Sebastian

  parent reply	other threads:[~2018-10-18 18:25 UTC|newest]

Thread overview: 57+ messages / expand[flat|nested]  mbox.gz  Atom feed  top
2018-10-04 14:05 [PATCH 00/11 v3] x86: load FPU registers on return to userland Sebastian Andrzej Siewior
2018-10-04 14:05 ` [PATCH 01/11] x86/entry: remove _TIF_ALLWORK_MASK Sebastian Andrzej Siewior
2018-10-11 16:27   ` Borislav Petkov
2018-10-04 14:05 ` [PATCH 02/11] x86/fpu: add (__)make_fpregs_active helpers Sebastian Andrzej Siewior
2018-10-04 14:05 ` [PATCH 03/11] x86/fpu: make __raw_xsave_addr() use feature number instead of mask Sebastian Andrzej Siewior
2018-10-11 17:30   ` Christophe de Dinechin
2018-10-18 11:19     ` Sebastian Andrzej Siewior
2018-10-12 15:52   ` Dave Hansen
2018-10-18 11:17     ` Sebastian Andrzej Siewior
2018-10-18 11:21       ` Sebastian Andrzej Siewior
2018-10-17 10:01   ` Borislav Petkov
2018-10-18 11:48     ` Sebastian Andrzej Siewior
2018-10-04 14:05 ` [PATCH 04/11] x86/fpu: eager switch PKRU state Sebastian Andrzej Siewior
2018-10-12 17:51   ` Dave Hansen
2018-10-12 18:09     ` Andy Lutomirski
2018-10-12 19:44       ` Dave Hansen
2018-10-18 16:13     ` Sebastian Andrzej Siewior
2018-10-18 17:50       ` Dave Hansen
2018-10-04 14:05 ` [PATCH 05/11] x86/fpu: set PKRU state for kernel threads Sebastian Andrzej Siewior
2018-10-12 17:54   ` Dave Hansen
2018-10-12 18:02     ` Andy Lutomirski
2018-10-18 16:26       ` Sebastian Andrzej Siewior
2018-10-18 16:48         ` Andy Lutomirski
2018-10-18 17:47           ` Dave Hansen
2018-10-18 18:25           ` Sebastian Andrzej Siewior [this message]
2018-10-18 20:46             ` Andy Lutomirski
2018-10-18 20:56               ` Dave Hansen
2018-10-18 21:24                 ` Sebastian Andrzej Siewior
2018-10-18 21:58                   ` Andy Lutomirski
2018-10-19  7:44               ` Paolo Bonzini
2018-10-19 16:59                 ` Andy Lutomirski
2018-10-19 17:01                   ` Dave Hansen
2018-10-19 17:37                     ` Andy Lutomirski
2018-10-19 18:26                       ` Dave Hansen
2018-10-04 14:05 ` [PATCH 06/11] x86/pkeys: make init_pkru_value static Sebastian Andrzej Siewior
2018-10-12 17:55   ` Dave Hansen
2018-10-04 14:05 ` [PATCH 07/11] x86/pkeys: Drop the preempt-disable section Sebastian Andrzej Siewior
2018-10-12 17:58   ` Dave Hansen
2018-10-12 18:07     ` Andy Lutomirski
2018-10-12 20:26       ` Sebastian Andrzej Siewior
2018-10-04 14:05 ` [PATCH 08/11] x86/fpu: Always store the registers in copy_fpstate_to_sigframe() Sebastian Andrzej Siewior
2018-10-11 17:50   ` Christophe de Dinechin
2018-10-11 21:18     ` Andy Lutomirski
2018-10-12 18:15   ` Dave Hansen
2018-11-02 14:42     ` Sebastian Andrzej Siewior
2018-10-04 14:05 ` [PATCH 09/11] x86/entry: add TIF_LOAD_FPU Sebastian Andrzej Siewior
2018-10-04 14:05 ` [PATCH 10/11] x86/fpu: prepare copy_fpstate_to_sigframe for TIF_LOAD_FPU Sebastian Andrzej Siewior
2018-10-12 19:40   ` Dave Hansen
2018-10-15 15:24     ` Borislav Petkov
2018-11-02 15:44       ` Sebastian Andrzej Siewior
2018-11-02 22:55     ` Sebastian Andrzej Siewior
2018-10-04 14:05 ` [PATCH 11/11] x86/fpu: defer FPU state load until return to userspace Sebastian Andrzej Siewior
2018-10-04 16:14   ` Andy Lutomirski
2018-10-12 20:25     ` Sebastian Andrzej Siewior
2018-10-04 16:45 ` [PATCH 00/11 v3] x86: load FPU registers on return to userland Rik van Riel
2018-10-04 16:50   ` Andy Lutomirski
2018-10-05 11:55   ` Sebastian Andrzej Siewior

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