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From: Dave Hansen <dave.hansen@intel.com>
To: Andy Lutomirski <luto@amacapital.net>, Fenghua Yu <fenghua.yu@intel.com>
Cc: Andy Lutomirski <luto@kernel.org>,
	Weiny Ira <ira.weiny@intel.com>,
	Thomas Gleixner <tglx@linutronix.de>,
	Ingo Molnar <mingo@redhat.com>, Borislav Petkov <bp@alien8.de>,
	Peter Zijlstra <peterz@infradead.org>,
	Dave Hansen <dave.hansen@linux.intel.com>,
	X86 ML <x86@kernel.org>, Dan Williams <dan.j.williams@intel.com>,
	Vishal Verma <vishal.l.verma@intel.com>,
	Andrew Morton <akpm@linux-foundation.org>,
	"open list:DOCUMENTATION" <linux-doc@vger.kernel.org>,
	LKML <linux-kernel@vger.kernel.org>,
	linux-nvdimm <linux-nvdimm@lists.01.org>,
	Linux FS Devel <linux-fsdevel@vger.kernel.org>,
	Linux-MM <linux-mm@kvack.org>,
	"open list:KERNEL SELFTEST FRAMEWORK" 
	<linux-kselftest@vger.kernel.org>
Subject: Re: [PATCH RFC V2 17/17] x86/entry: Preserve PKRS MSR across exceptions
Date: Thu, 23 Jul 2020 10:30:31 -0700	[thread overview]
Message-ID: <71f0e3d8-6dfa-742d-eaa7-330b59611e2f@intel.com> (raw)
In-Reply-To: <C03DA782-BD1A-42E3-B118-ABB34BC5F2AF@amacapital.net>

On 7/23/20 10:08 AM, Andy Lutomirski wrote:
> Suppose some kernel code (a syscall or kernel thread) changes PKRS
> then takes a page fault. The page fault handler needs a fresh PKRS.
> Then the page fault handler (say a VMA’s .fault handler) changes
> PKRS.  The we get an interrupt. The interrupt *also* needs a fresh
> PKRS and the page fault value needs to be saved somewhere.
> 
> So we have more than one saved value per thread, and thread_struct
> isn’t going to solve this problem.

Taking a step back...  This is all true only if we decide that we want
protection keys to provide protection during exceptions and interrupts.
 Right now, the code supports nesting:

	kmap(foo);
		kmap(bar);
		kunmap(bar);
	kunmap(foo);

with a reference count.  So, the nested kmap() will see the count
elevated and do nothing.

I'm generally OK with this getting merged without extending PKS
protection to interrupts and exceptions.  Ira and Fenghua should
certainly give it a go, but I'd like to see it as an add-on feature and
we can judge the benefits versus complexity separately.

Ira was looking at adding it because it _looked_ simple.  Andy has me
really scared about it now. :)


  reply	other threads:[~2020-07-23 17:30 UTC|newest]

Thread overview: 73+ messages / expand[flat|nested]  mbox.gz  Atom feed  top
2020-07-17  7:20 [PATCH RFC V2 00/17] PKS: Add Protection Keys Supervisor (PKS) support ira.weiny
2020-07-17  7:20 ` [PATCH RFC V2 01/17] x86/pkeys: Create pkeys_internal.h ira.weiny
2020-07-17  7:20 ` [PATCH RFC V2 02/17] x86/fpu: Refactor arch_set_user_pkey_access() for PKS support ira.weiny
2020-07-17  8:54   ` Peter Zijlstra
2020-07-17 20:52     ` Ira Weiny
2020-07-20  9:14       ` Peter Zijlstra
2020-07-17 22:36     ` Dave Hansen
2020-07-20  9:13       ` Peter Zijlstra
2020-07-17  7:20 ` [PATCH RFC V2 03/17] x86/pks: Enable Protection Keys Supervisor (PKS) ira.weiny
2020-07-17  7:20 ` [PATCH RFC V2 04/17] x86/pks: Preserve the PKRS MSR on context switch ira.weiny
2020-07-17  8:31   ` Peter Zijlstra
2020-07-17 21:39     ` Ira Weiny
2020-07-17  8:59   ` Peter Zijlstra
2020-07-17 22:34     ` Ira Weiny
2020-07-20  9:15       ` Peter Zijlstra
2020-07-20 18:35         ` Ira Weiny
2020-07-17  7:20 ` [PATCH RFC V2 05/17] x86/pks: Add PKS kernel API ira.weiny
2020-07-17  7:20 ` [PATCH RFC V2 06/17] x86/pks: Add a debugfs file for allocated PKS keys ira.weiny
2020-07-17  7:20 ` [PATCH RFC V2 07/17] Documentation/pkeys: Update documentation for kernel pkeys ira.weiny
2020-07-17  7:20 ` [PATCH RFC V2 08/17] x86/pks: Add PKS Test code ira.weiny
2020-07-17  7:20 ` [PATCH RFC V2 09/17] memremap: Convert devmap static branch to {inc,dec} ira.weiny
2020-07-17  7:20 ` [PATCH RFC V2 10/17] fs/dax: Remove unused size parameter ira.weiny
2020-07-17  7:20 ` [PATCH RFC V2 11/17] drivers/dax: Expand lock scope to cover the use of addresses ira.weiny
2020-07-17  7:20 ` [PATCH RFC V2 12/17] memremap: Add zone device access protection ira.weiny
2020-07-17  9:10   ` Peter Zijlstra
2020-07-18  5:06     ` Ira Weiny
2020-07-20  9:16       ` Peter Zijlstra
2020-07-17  9:17   ` Peter Zijlstra
2020-07-18  5:51     ` Ira Weiny
2020-07-17  9:20   ` Peter Zijlstra
2020-07-17  7:20 ` [PATCH RFC V2 13/17] kmap: Add stray write protection for device pages ira.weiny
2020-07-17  9:21   ` Peter Zijlstra
2020-07-19  4:13     ` Ira Weiny
2020-07-20  9:17       ` Peter Zijlstra
2020-07-21 16:31         ` Ira Weiny
2020-07-17  7:20 ` [PATCH RFC V2 14/17] dax: Stray write protection for dax_direct_access() ira.weiny
2020-07-17  9:22   ` Peter Zijlstra
2020-07-19  4:41     ` Ira Weiny
2020-07-17  7:20 ` [PATCH RFC V2 15/17] nvdimm/pmem: Stray write protection for pmem->virt_addr ira.weiny
2020-07-17  7:20 ` [PATCH RFC V2 16/17] [dax|pmem]: Enable stray write protection ira.weiny
2020-07-17  9:25   ` Peter Zijlstra
2020-07-17  7:20 ` [PATCH RFC V2 17/17] x86/entry: Preserve PKRS MSR across exceptions ira.weiny
2020-07-17  9:30   ` Peter Zijlstra
2020-07-21 18:01     ` Ira Weiny
2020-07-21 19:11       ` Peter Zijlstra
2020-07-17  9:34   ` Peter Zijlstra
2020-07-17 10:06   ` Peter Zijlstra
2020-07-22  5:27     ` Ira Weiny
2020-07-22  9:48       ` Peter Zijlstra
2020-07-22 21:24         ` Ira Weiny
2020-07-23 20:08       ` Thomas Gleixner
2020-07-23 20:15         ` Thomas Gleixner
2020-07-24 17:23           ` Ira Weiny
2020-07-24 17:29             ` Andy Lutomirski
2020-07-24 19:43               ` Ira Weiny
2020-07-22 16:21   ` Andy Lutomirski
2020-07-23 16:18     ` Fenghua Yu
2020-07-23 16:23       ` Dave Hansen
2020-07-23 16:52         ` Fenghua Yu
2020-07-23 17:08           ` Andy Lutomirski
2020-07-23 17:30             ` Dave Hansen [this message]
2020-07-23 20:23               ` Thomas Gleixner
2020-07-23 20:22             ` Thomas Gleixner
2020-07-23 21:30               ` Andy Lutomirski
2020-07-23 22:14                 ` Thomas Gleixner
2020-07-23 19:53   ` Thomas Gleixner
2020-07-23 22:04     ` Ira Weiny
2020-07-23 23:41       ` Thomas Gleixner
2020-07-24 21:24         ` Thomas Gleixner
2020-07-24 21:31           ` Thomas Gleixner
2020-07-25  0:09           ` Andy Lutomirski
2020-07-27 20:59           ` Ira Weiny
2020-07-24 22:19 ` [PATCH RFC V2 00/17] PKS: Add Protection Keys Supervisor (PKS) support Kees Cook

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