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

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Message-ID: <20190520075232.GA30972@quack2.suse.cz>
Date:   Mon, 20 May 2019 09:52:32 +0200
From:   Jan Kara <jack@...e.cz>
To:     Dan Williams <dan.j.williams@...el.com>
Cc:     Kees Cook <keescook@...omium.org>, Jan Kara <jack@...e.cz>,
        linux-nvdimm <linux-nvdimm@...ts.01.org>,
        stable <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 <linux-fsdevel@...r.kernel.org>,
        Linux Kernel Mailing List <linux-kernel@...r.kernel.org>
Subject: Re: [PATCH] libnvdimm/pmem: Bypass CONFIG_HARDENED_USERCOPY overhead

On Sat 18-05-19 21:46:03, Dan Williams wrote:
> On Fri, May 17, 2019 at 12:25 PM Kees Cook <keescook@...omium.org> wrote:
> > On Fri, May 17, 2019 at 10:28:48AM -0700, Dan Williams wrote:
> > > It seems dax_iomap_actor() is not a path where we'd be worried about
> > > needing hardened user copy checks.
> >
> > I would agree: I think the proposed patch makes sense. :)
> 
> Sounds like an acked-by to me.

Yeah, if Kees agrees, I'm fine with skipping the checks as well. I just
wanted that to be clarified. Also it helped me that you wrote:

That routine (dax_iomap_actor()) validates that the logical file offset is
within bounds of the file, then it does a sector-to-pfn translation which
validates that the physical mapping is within bounds of the block device.

That is more specific than "dax_iomap_actor() takes care of necessary
checks" which was in the changelog. And the above paragraph helped me
clarify which checks in dax_iomap_actor() you think replace those usercopy
checks. So I think it would be good to add that paragraph to those
copy_from_pmem() functions as a comment just in case we are wondering in
the future why we are skipping the checks... Also feel free to add:

Acked-by: Jan Kara <jack@...e.cz>

								Honza
-- 
Jan Kara <jack@...e.com>
SUSE Labs, CR