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

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Date:   Mon, 20 May 2019 08:40:48 -0700
From:   Dan Williams <dan.j.williams@...el.com>
To:     Jan Kara <jack@...e.cz>
Cc:     Kees Cook <keescook@...omium.org>,
        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 Mon, May 20, 2019 at 12:52 AM Jan Kara <jack@...e.cz> wrote:
>
> 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>

Will do, thanks Jan.