linux-kernel - Re: [PATCH] libnvdimm/pmem: Bypass CONFIG_HARDENED

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Date:   Fri, 17 May 2019 09:40:31 -0700
From:   Kees Cook <keescook@...omium.org>
To:     David Laight <David.Laight@...LAB.COM>
Cc:     'Jan Kara' <jack@...e.cz>, Dan Williams <dan.j.williams@...el.com>,
        "linux-nvdimm@...ts.01.org" <linux-nvdimm@...ts.01.org>,
        "stable@...r.kernel.org" <stable@...r.kernel.org>,
        Jeff Moyer <jmoyer@...hat.com>, Ingo Molnar <mingo@...hat.com>,
        Christoph Hellwig <hch@....de>,
        Al Viro <viro@...iv.linux.org.uk>,
        Thomas Gleixner <tglx@...utronix.de>,
        Matthew Wilcox <willy@...radead.org>,
        Jeff Smits <jeff.smits@...el.com>,
        "linux-fsdevel@...r.kernel.org" <linux-fsdevel@...r.kernel.org>,
        "linux-kernel@...r.kernel.org" <linux-kernel@...r.kernel.org>
Subject: Re: [PATCH] libnvdimm/pmem: Bypass CONFIG_HARDENED_USERCOPY overhead

On Fri, May 17, 2019 at 04:14:03PM +0000, David Laight wrote:
> From: Kees Cook
> > Sent: 17 May 2019 16:54
> ...
> > > I've changed some of our code to use __get_user() to avoid
> > > these stupid overheads.
> > 
> > __get_user() skips even access_ok() checking too, so that doesn't seem
> > like a good idea. Did you run access_ok() checks separately? (This
> > generally isn't recommended.)
> 
> Of course, I'm not THAT stupid :-)

Right, yes, I know. :) I just wanted to double-check since accidents
can happen. The number of underscores on these function is not really
a great way to indicate what they're doing. ;)

-- 
Kees Cook