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Date: Wed, 24 Oct 2018 15:56:06 +0100
From: Tycho Andersen <tycho@...ho.ws>
To: Igor Stoppa <igor.stoppa@...il.com>
Cc: Mathieu Desnoyers <mathieu.desnoyers@...icios.com>,
Mimi Zohar <zohar@...ux.vnet.ibm.com>,
Kees Cook <keescook@...omium.org>,
Matthew Wilcox <willy@...radead.org>,
Dave Chinner <david@...morbit.com>,
James Morris <jmorris@...ei.org>, Michal Hocko <mhocko@...nel.org>,
kernel-hardening@...ts.openwall.com,
linux-integrity@...r.kernel.org,
linux-security-module@...r.kernel.org,
igor stoppa <igor.stoppa@...wei.com>,
Dave Hansen <dave.hansen@...ux.intel.com>,
Jonathan Corbet <corbet@....net>, Laura Abbott <labbott@...hat.com>,
Thomas Gleixner <tglx@...utronix.de>,
Kate Stewart <kstewart@...uxfoundation.org>,
"David S. Miller" <davem@...emloft.net>,
Greg Kroah-Hartman <gregkh@...uxfoundation.org>,
Philippe Ombredanne <pombredanne@...b.com>,
"Paul E. McKenney" <paulmck@...ux.vnet.ibm.com>,
Josh Triplett <josh@...htriplett.org>,
rostedt <rostedt@...dmis.org>,
Lai Jiangshan <jiangshanlai@...il.com>,
linux-kernel <linux-kernel@...r.kernel.org>
Subject: Re: [PATCH 14/17] prmem: llist, hlist, both plain and rcu
On Wed, Oct 24, 2018 at 05:03:01PM +0300, Igor Stoppa wrote:
> On 24/10/18 14:37, Mathieu Desnoyers wrote:
> > Also, is it the right approach to duplicate existing APIs, or should we
> > rather hook into page fault handlers and let the kernel do those "shadow"
> > mappings under the hood ?
>
> This question is probably a good candidate for the small Q&A section I have
> in the 00/17.
>
>
> > Adding a new GFP flags for dynamic allocation, and a macro mapping to
> > a section attribute might suffice for allocation or definition of such
> > mostly-read-only/seldom-updated data.
>
> I think what you are proposing makes sense from a pure hardening standpoint.
> From a more defensive one, I'd rather minimise the chances of giving a free
> pass to an attacker.
>
> Maybe there is a better implementation of this, than what I have in mind.
> But, based on my current understanding of what you are describing, there
> would be few issues:
>
> 1) where would the pool go? The pool is a way to manage multiple vmas and
> express common property they share. Even before a vma is associated to the
> pool.
>
> 2) there would be more code that can seamlessly deal with both protected and
> regular data. Based on what? Some parameter, I suppose.
> That parameter would be the new target.
> If the code is "duplicated", as you say, the actual differences are baked in
> at compile time. The "duplication" would also allow to have always inlined
> functions for write-rare and leave more freedom to the compiler for their
> non-protected version.
>
> Besides, I think the separate wr version also makes it very clear, to the
> user of the API, that there will be a price to pay, in terms of performance.
> The more seamlessly alternative might make this price less obvious.
What about something in the middle, where we move list to list_impl.h,
and add a few macros where you have list_set_prev() in prlist now, so
we could do,
// prlist.h
#define list_set_next(head, next) wr_ptr(&head->next, next)
#define list_set_prev(head, prev) wr_ptr(&head->prev, prev)
#include <linux/list_impl.h>
// list.h
#define list_set_next(next) (head->next = next)
#define list_set_next(prev) (head->prev = prev)
#include <linux/list_impl.h>
I wonder then if you can get rid of some of the type punning too? It's
not clear exactly why that's necessary from the series, but perhaps
I'm missing something obvious :)
I also wonder how much the actual differences being baked in at
compile time makes. Most (all?) of this code is inlined.
Cheers,
Tycho
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