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From: Peter Zijlstra <peterz@infradead.org>
To: Igor Stoppa <igor.stoppa@gmail.com>
Cc: Mimi Zohar <zohar@linux.vnet.ibm.com>,
	Kees Cook <keescook@chromium.org>,
	Matthew Wilcox <willy@infradead.org>,
	Dave Chinner <david@fromorbit.com>,
	James Morris <jmorris@namei.org>,
	Michal Hocko <mhocko@kernel.org>,
	kernel-hardening@lists.openwall.com,
	linux-integrity@vger.kernel.org,
	linux-security-module@vger.kernel.org, igor.stoppa@huawei.com,
	Dave Hansen <dave.hansen@linux.intel.com>,
	Jonathan Corbet <corbet@lwn.net>,
	Laura Abbott <labbott@redhat.com>,
	Will Deacon <will.deacon@arm.com>,
	Boqun Feng <boqun.feng@gmail.com>, Arnd Bergmann <arnd@arndb.de>,
	linux-arch@vger.kernel.org, linux-kernel@vger.kernel.org
Subject: Re: [PATCH 16/17] prmem: pratomic-long
Date: Tue, 30 Oct 2018 16:58:41 +0100
Message-ID: <20181030155841.GF8177@hirez.programming.kicks-ass.net> (raw)
In-Reply-To: <806bfff0-8d62-9918-480d-ec791b93841e@gmail.com>

On Mon, Oct 29, 2018 at 11:17:14PM +0200, Igor Stoppa wrote:
> 
> 
> On 25/10/2018 01:13, Peter Zijlstra wrote:
> > On Wed, Oct 24, 2018 at 12:35:03AM +0300, Igor Stoppa wrote:
> > > +static __always_inline
> > > +bool __pratomic_long_op(bool inc, struct pratomic_long_t *l)
> > > +{
> > > +	struct page *page;
> > > +	uintptr_t base;
> > > +	uintptr_t offset;
> > > +	unsigned long flags;
> > > +	size_t size = sizeof(*l);
> > > +	bool is_virt = __is_wr_after_init(l, size);
> > > +
> > > +	if (WARN(!(is_virt || likely(__is_wr_pool(l, size))),
> > > +		 WR_ERR_RANGE_MSG))
> > > +		return false;
> > > +	local_irq_save(flags);
> > > +	if (is_virt)
> > > +		page = virt_to_page(l);
> > > +	else
> > > +		vmalloc_to_page(l);
> > > +	offset = (~PAGE_MASK) & (uintptr_t)l;
> > > +	base = (uintptr_t)vmap(&page, 1, VM_MAP, PAGE_KERNEL);
> > > +	if (WARN(!base, WR_ERR_PAGE_MSG)) {
> > > +		local_irq_restore(flags);
> > > +		return false;
> > > +	}
> > > +	if (inc)
> > > +		atomic_long_inc((atomic_long_t *)(base + offset));
> > > +	else
> > > +		atomic_long_dec((atomic_long_t *)(base + offset));
> > > +	vunmap((void *)base);
> > > +	local_irq_restore(flags);
> > > +	return true;
> > > +
> > > +}
> > 
> > That's just hideously nasty.. and horribly broken.
> > 
> > We're not going to duplicate all these kernel interfaces wrapped in gunk
> > like that.
> 
> one possibility would be to have macros which use typeof() on the parameter
> being passed, to decide what implementation to use: regular or write-rare
> 
> This means that type punning would still be needed, to select the
> implementation.
> 
> Would this be enough? Is there some better way?

Like mentioned elsewhere; if you do write_enable() + write_disable()
thingies, it all becomes:

	write_enable();
	atomic_foo(&bar);
	write_disable();

No magic gunk infested duplication at all. Of course, ideally you'd then
teach objtool about this (or a GCC plugin I suppose) to ensure any
enable reached a disable.

The alternative is something like:

#define ALLOW_WRITE(stmt) do { write_enable(); do { stmt; } while (0); write_disable(); } while (0)

which then allows you to write:

	ALLOW_WRITE(atomic_foo(&bar));

No duplication.

> > Also, you _cannot_ call vunmap() with IRQs disabled. Clearly
> > you've never tested this with debug bits enabled.
> 
> I thought I had them. And I _did_ have them enabled, at some point.
> But I must have messed up with the configuration and I failed to notice
> this.
> 
> I can think of a way it might work, albeit it's not going to be very pretty:
> 
> * for the vmap(): if I understand correctly, it might sleep while obtaining
> memory for creating the mapping. This part could be executed before
> disabling interrupts. The rest of the function, instead, would be executed
> after interrupts are disabled.
> 
> * for vunmap(): after the writing is done, change also the alternate mapping
> to read only, then enable interrupts and destroy the alternate mapping.
> Making also the secondary mapping read only makes it equally secure as the
> primary, which means that it can be visible also with interrupts enabled.

That doesn't work if you wanted to do this write while you already have
IRQs disabled for example.



  reply index

Thread overview: 140+ messages / expand[flat|nested]  mbox.gz  Atom feed  top
2018-10-23 21:34 [RFC v1 PATCH 00/17] prmem: protected memory Igor Stoppa
2018-10-23 21:34 ` [PATCH 01/17] prmem: linker section for static write rare Igor Stoppa
2018-10-23 21:34 ` [PATCH 02/17] prmem: write rare for static allocation Igor Stoppa
2018-10-25  0:24   ` Dave Hansen
2018-10-29 18:03     ` Igor Stoppa
2018-10-26  9:41   ` Peter Zijlstra
2018-10-29 20:01     ` Igor Stoppa
2018-10-23 21:34 ` [PATCH 03/17] prmem: vmalloc support for dynamic allocation Igor Stoppa
2018-10-25  0:26   ` Dave Hansen
2018-10-29 18:07     ` Igor Stoppa
2018-10-23 21:34 ` [PATCH 04/17] prmem: " Igor Stoppa
2018-10-23 21:34 ` [PATCH 05/17] prmem: shorthands for write rare on common types Igor Stoppa
2018-10-25  0:28   ` Dave Hansen
2018-10-29 18:12     ` Igor Stoppa
2018-10-23 21:34 ` [PATCH 06/17] prmem: test cases for memory protection Igor Stoppa
2018-10-24  3:27   ` Randy Dunlap
2018-10-24 14:24     ` Igor Stoppa
2018-10-25 16:43   ` Dave Hansen
2018-10-29 18:16     ` Igor Stoppa
2018-10-23 21:34 ` [PATCH 07/17] prmem: lkdtm tests " Igor Stoppa
2018-10-23 21:34 ` [PATCH 08/17] prmem: struct page: track vmap_area Igor Stoppa
2018-10-24  3:12   ` Matthew Wilcox
2018-10-24 23:01     ` Igor Stoppa
2018-10-25  2:13       ` Matthew Wilcox
2018-10-29 18:21         ` Igor Stoppa
2018-10-23 21:34 ` [PATCH 09/17] prmem: hardened usercopy Igor Stoppa
2018-10-29 11:45   ` Chris von Recklinghausen
2018-10-29 18:24     ` Igor Stoppa
2018-10-23 21:34 ` [PATCH 10/17] prmem: documentation Igor Stoppa
2018-10-24  3:48   ` Randy Dunlap
2018-10-24 14:30     ` Igor Stoppa
2018-10-24 23:04   ` Mike Rapoport
2018-10-29 19:05     ` Igor Stoppa
2018-10-26  9:26   ` Peter Zijlstra
2018-10-26 10:20     ` Matthew Wilcox
2018-10-29 19:28       ` Igor Stoppa
2018-10-26 10:46     ` Kees Cook
2018-10-28 18:31       ` Peter Zijlstra
2018-10-29 21:04         ` Igor Stoppa
2018-10-30 15:26           ` Peter Zijlstra
2018-10-30 16:37             ` Kees Cook
2018-10-30 17:06               ` Andy Lutomirski
2018-10-30 17:58                 ` Matthew Wilcox
2018-10-30 18:03                   ` Dave Hansen
2018-10-31  9:18                     ` Peter Zijlstra
2018-10-30 18:28                   ` Tycho Andersen
2018-10-30 19:20                     ` Matthew Wilcox
2018-10-30 20:43                       ` Igor Stoppa
2018-10-30 21:02                         ` Andy Lutomirski
2018-10-30 21:07                           ` Kees Cook
2018-10-30 21:25                             ` Igor Stoppa
2018-10-30 22:15                           ` Igor Stoppa
2018-10-31 10:11                             ` Peter Zijlstra
2018-10-31 20:38                               ` Andy Lutomirski
2018-10-31 20:53                                 ` Andy Lutomirski
2018-10-31  9:45                           ` Peter Zijlstra
2018-10-30 21:35                         ` Matthew Wilcox
2018-10-30 21:49                           ` Igor Stoppa
2018-10-31  4:41                           ` Andy Lutomirski
2018-10-31  9:08                             ` Igor Stoppa
2018-10-31 19:38                               ` Igor Stoppa
2018-10-31 10:02                             ` Peter Zijlstra
2018-10-31 20:36                               ` Andy Lutomirski
2018-10-31 21:00                                 ` Peter Zijlstra
2018-10-31 22:57                                   ` Andy Lutomirski
2018-10-31 23:10                                     ` Igor Stoppa
2018-10-31 23:19                                       ` Andy Lutomirski
2018-10-31 23:26                                         ` Igor Stoppa
2018-11-01  8:21                                           ` Thomas Gleixner
2018-11-01 15:58                                             ` Igor Stoppa
2018-11-01 17:08                                     ` Peter Zijlstra
2018-10-30 18:51                   ` Andy Lutomirski
2018-10-30 19:14                     ` Kees Cook
2018-10-30 21:25                     ` Matthew Wilcox
2018-10-30 21:55                       ` Igor Stoppa
2018-10-30 22:08                         ` Matthew Wilcox
2018-10-31  9:29                       ` Peter Zijlstra
2018-10-30 23:18                     ` Nadav Amit
2018-10-31  9:08                       ` Peter Zijlstra
2018-11-01 16:31                         ` Nadav Amit
2018-11-02 21:11                           ` Nadav Amit
2018-10-31  9:36                   ` Peter Zijlstra
2018-10-31 11:33                     ` Matthew Wilcox
2018-11-13 14:25                 ` Igor Stoppa
2018-11-13 17:16                   ` Andy Lutomirski
2018-11-13 17:43                     ` Nadav Amit
2018-11-13 17:47                       ` Andy Lutomirski
2018-11-13 18:06                         ` Nadav Amit
2018-11-13 18:31                         ` Igor Stoppa
2018-11-13 18:33                           ` Igor Stoppa
2018-11-13 18:36                             ` Andy Lutomirski
2018-11-13 19:03                               ` Igor Stoppa
2018-11-21 16:34                               ` Igor Stoppa
2018-11-21 17:36                                 ` Nadav Amit
2018-11-21 18:01                                   ` Igor Stoppa
2018-11-21 18:15                                 ` Andy Lutomirski
2018-11-22 19:27                                   ` Igor Stoppa
2018-11-22 20:04                                     ` Matthew Wilcox
2018-11-22 20:53                                       ` Andy Lutomirski
2018-12-04 12:34                                         ` Igor Stoppa
2018-11-13 18:48                           ` Andy Lutomirski
2018-11-13 19:35                             ` Igor Stoppa
2018-11-13 18:26                     ` Igor Stoppa
2018-11-13 18:35                       ` Andy Lutomirski
2018-11-13 19:01                         ` Igor Stoppa
2018-10-31  9:27               ` Igor Stoppa
2018-10-26 11:09     ` Markus Heiser
2018-10-29 19:35       ` Igor Stoppa
2018-10-26 15:05     ` Jonathan Corbet
2018-10-29 19:38       ` Igor Stoppa
2018-10-29 20:35     ` Igor Stoppa
2018-10-23 21:34 ` [PATCH 11/17] prmem: llist: use designated initializer Igor Stoppa
2018-10-23 21:34 ` [PATCH 12/17] prmem: linked list: set alignment Igor Stoppa
2018-10-26  9:31   ` Peter Zijlstra
2018-10-23 21:35 ` [PATCH 13/17] prmem: linked list: disable layout randomization Igor Stoppa
2018-10-24 13:43   ` Alexey Dobriyan
2018-10-29 19:40     ` Igor Stoppa
2018-10-26  9:32   ` Peter Zijlstra
2018-10-26 10:17     ` Matthew Wilcox
2018-10-30 15:39       ` Peter Zijlstra
2018-10-23 21:35 ` [PATCH 14/17] prmem: llist, hlist, both plain and rcu Igor Stoppa
2018-10-24 11:37   ` Mathieu Desnoyers
2018-10-24 14:03     ` Igor Stoppa
2018-10-24 14:56       ` Tycho Andersen
2018-10-24 22:52         ` Igor Stoppa
2018-10-25  8:11           ` Tycho Andersen
2018-10-28  9:52       ` Steven Rostedt
2018-10-29 19:43         ` Igor Stoppa
2018-10-26  9:38   ` Peter Zijlstra
2018-10-23 21:35 ` [PATCH 15/17] prmem: test cases for prlist and prhlist Igor Stoppa
2018-10-23 21:35 ` [PATCH 16/17] prmem: pratomic-long Igor Stoppa
2018-10-25  0:13   ` Peter Zijlstra
2018-10-29 21:17     ` Igor Stoppa
2018-10-30 15:58       ` Peter Zijlstra [this message]
2018-10-30 16:28         ` Will Deacon
2018-10-31  9:10           ` Peter Zijlstra
2018-11-01  3:28             ` Kees Cook
2018-10-23 21:35 ` [PATCH 17/17] prmem: ima: turn the measurements list write rare Igor Stoppa
2018-10-24 23:03 ` [RFC v1 PATCH 00/17] prmem: protected memory Dave Chinner
2018-10-29 19:47   ` Igor Stoppa

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