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From: Ard Biesheuvel <ard.biesheuvel@linaro.org>
To: Peter Zijlstra <peterz@infradead.org>
Cc: Andy Lutomirski <luto@amacapital.net>,
	Andy Lutomirski <luto@kernel.org>,
	Will Deacon <will.deacon@arm.com>,
	Mark Rutland <mark.rutland@arm.com>,
	Matt Fleming <matt@codeblueprint.co.uk>,
	Sai Praneeth Prakhya <sai.praneeth.prakhya@intel.com>,
	"linux-efi@vger.kernel.org" <linux-efi@vger.kernel.org>,
	"linux-kernel@vger.kernel.org" <linux-kernel@vger.kernel.org>,
	joeyli <jlee@suse.com>, Borislav Petkov <bp@alien8.de>,
	"Michael S. Tsirkin" <mst@redhat.com>,
	"Neri, Ricardo" <ricardo.neri@intel.com>,
	"Ravi V. Shankar" <ravi.v.shankar@intel.com>
Subject: Re: [PATCH 3/3] x86/efi: Use efi_switch_mm() rather than manually twiddling with cr3
Date: Mon, 21 Aug 2017 17:08:50 +0100	[thread overview]
Message-ID: <CAKv+Gu_whUkAdM4xHLs-Cm90hRmqBbVgyDTyBVrGoTO1G6WzLg@mail.gmail.com> (raw)
In-Reply-To: <20170821155913.7bmmy7zaihpd6s7h@hirez.programming.kicks-ass.net>

On 21 August 2017 at 16:59, Peter Zijlstra <peterz@infradead.org> wrote:
> On Mon, Aug 21, 2017 at 08:23:10AM -0700, Andy Lutomirski wrote:
>> > Ah, but only root can create per-cpu events or attach events to kernel
>> > threads (with sensible paranoia levels).
>>
>> But this may not need to be percpu.  If a non root user can trigger, say, an EFI variable read in their own thread context, boom.
>
> I was going by the proposed: "everything EFI in a kthread" model. But
> yes, if that's not done, then you're quite right.
>

How does this work in cases where we need to call into UEFI from
non-process context? Or at least from a context where current != EFI's
kthread. We have EFI pstore code, for instance, that records panic
data. Should we make an exception for those?

I'm happy to have a stab at implementing the EFI kthread, but I'd like
to get some of these details clarified first.

WARNING: multiple messages have this Message-ID (diff)
From: Ard Biesheuvel <ard.biesheuvel-QSEj5FYQhm4dnm+yROfE0A@public.gmane.org>
To: Peter Zijlstra <peterz-wEGCiKHe2LqWVfeAwA7xHQ@public.gmane.org>
Cc: Andy Lutomirski <luto-kltTT9wpgjJwATOyAt5JVQ@public.gmane.org>,
	Andy Lutomirski <luto-DgEjT+Ai2ygdnm+yROfE0A@public.gmane.org>,
	Will Deacon <will.deacon-5wv7dgnIgG8@public.gmane.org>,
	Mark Rutland <mark.rutland-5wv7dgnIgG8@public.gmane.org>,
	Matt Fleming
	<matt-mF/unelCI9GS6iBeEJttW/XRex20P6io@public.gmane.org>,
	Sai Praneeth Prakhya
	<sai.praneeth.prakhya-ral2JQCrhuEAvxtiuMwx3w@public.gmane.org>,
	"linux-efi-u79uwXL29TY76Z2rM5mHXA@public.gmane.org"
	<linux-efi-u79uwXL29TY76Z2rM5mHXA@public.gmane.org>,
	"linux-kernel-u79uwXL29TY76Z2rM5mHXA@public.gmane.org"
	<linux-kernel-u79uwXL29TY76Z2rM5mHXA@public.gmane.org>,
	joeyli <jlee-IBi9RG/b67k@public.gmane.org>,
	Borislav Petkov <bp-Gina5bIWoIWzQB+pC5nmwQ@public.gmane.org>,
	"Michael S. Tsirkin"
	<mst-H+wXaHxf7aLQT0dZR+AlfA@public.gmane.org>,
	"Neri,
	Ricardo" <ricardo.neri-ral2JQCrhuEAvxtiuMwx3w@public.gmane.org>,
	"Ravi V. Shankar"
	<ravi.v.shankar-ral2JQCrhuEAvxtiuMwx3w@public.gmane.org>
Subject: Re: [PATCH 3/3] x86/efi: Use efi_switch_mm() rather than manually twiddling with cr3
Date: Mon, 21 Aug 2017 17:08:50 +0100	[thread overview]
Message-ID: <CAKv+Gu_whUkAdM4xHLs-Cm90hRmqBbVgyDTyBVrGoTO1G6WzLg@mail.gmail.com> (raw)
In-Reply-To: <20170821155913.7bmmy7zaihpd6s7h-Nxj+rRp3nVydTX5a5knrm8zTDFooKrT+cvkQGrU6aU0@public.gmane.org>

On 21 August 2017 at 16:59, Peter Zijlstra <peterz-wEGCiKHe2LqWVfeAwA7xHQ@public.gmane.org> wrote:
> On Mon, Aug 21, 2017 at 08:23:10AM -0700, Andy Lutomirski wrote:
>> > Ah, but only root can create per-cpu events or attach events to kernel
>> > threads (with sensible paranoia levels).
>>
>> But this may not need to be percpu.  If a non root user can trigger, say, an EFI variable read in their own thread context, boom.
>
> I was going by the proposed: "everything EFI in a kthread" model. But
> yes, if that's not done, then you're quite right.
>

How does this work in cases where we need to call into UEFI from
non-process context? Or at least from a context where current != EFI's
kthread. We have EFI pstore code, for instance, that records panic
data. Should we make an exception for those?

I'm happy to have a stab at implementing the EFI kthread, but I'd like
to get some of these details clarified first.

  reply	other threads:[~2017-08-21 16:08 UTC|newest]

Thread overview: 44+ messages / expand[flat|nested]  mbox.gz  Atom feed  top
2017-08-15 19:18 [PATCH 0/3] Use mm_struct and switch_mm() instead of manually Sai Praneeth Prakhya
2017-08-15 19:18 ` [PATCH 1/3] efi: Use efi_mm in x86 as well as ARM Sai Praneeth Prakhya
2017-08-15 19:18 ` [PATCH 2/3] x86/efi: Replace efi_pgd with efi_mm.pgd Sai Praneeth Prakhya
2017-08-15 19:18   ` Sai Praneeth Prakhya
2017-08-15 19:18 ` [PATCH 3/3] x86/efi: Use efi_switch_mm() rather than manually twiddling with cr3 Sai Praneeth Prakhya
2017-08-15 21:46   ` Andy Lutomirski
2017-08-16  0:23     ` Sai Praneeth Prakhya
2017-08-16  0:23       ` Sai Praneeth Prakhya
2017-08-16  0:47       ` Andy Lutomirski
2017-08-16  0:47         ` Andy Lutomirski
2017-08-16  9:31     ` Ard Biesheuvel
2017-08-16  9:53       ` Mark Rutland
2017-08-16  9:53         ` Mark Rutland
2017-08-16 10:07         ` Will Deacon
2017-08-16 10:07           ` Will Deacon
2017-08-16 11:03           ` Mark Rutland
2017-08-16 12:57             ` Matt Fleming
2017-08-16 12:57               ` Matt Fleming
2017-08-16 16:14               ` Andy Lutomirski
2017-08-16 16:14                 ` Andy Lutomirski
2017-08-15 22:35                 ` Mark Rutland
2017-08-17 10:35                   ` Will Deacon
2017-08-17 15:52                     ` Andy Lutomirski
2017-08-17 15:52                       ` Andy Lutomirski
2017-08-21 10:33                       ` Peter Zijlstra
2017-08-21 10:33                         ` Peter Zijlstra
2017-08-21 13:56                         ` Andy Lutomirski
2017-08-21 13:56                           ` Andy Lutomirski
2017-08-21 14:08                           ` Peter Zijlstra
2017-08-21 15:23                             ` Andy Lutomirski
2017-08-21 15:23                               ` Andy Lutomirski
2017-08-21 15:59                               ` Peter Zijlstra
2017-08-21 15:59                                 ` Peter Zijlstra
2017-08-21 16:08                                 ` Ard Biesheuvel [this message]
2017-08-21 16:08                                   ` Ard Biesheuvel
2017-08-23 22:52                               ` Sai Praneeth Prakhya
2017-08-23 22:52                                 ` Sai Praneeth Prakhya
2017-08-25 15:13                                 ` Andy Lutomirski
2017-08-25 15:13                                   ` Andy Lutomirski
2017-08-21 17:24                           ` Peter Zijlstra
2017-08-25  2:36     ` Sai Praneeth Prakhya
2017-08-25 15:13       ` Andy Lutomirski
2017-12-17  0:06 [PATCH 3/3] x86/efi: Use efi_switch_mm() rather than manually twiddling with %cr3 Sai Praneeth Prakhya
2017-12-17  0:06 ` Sai Praneeth Prakhya

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