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

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Message-ID: <201905170855.8E2E1AC616@keescook>
Date:   Fri, 17 May 2019 08:56:52 -0700
From:   Kees Cook <keescook@...omium.org>
To:     Dan Williams <dan.j.williams@...el.com>
Cc:     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 Fri, May 17, 2019 at 08:08:27AM -0700, Dan Williams wrote:
> As far as I can see it's mostly check_heap_object() that is the
> problem, so I'm open to finding a way to just bypass that sub-routine.
> However, as far as I can see none of the other block / filesystem user
> copy implementations submit to the hardened checks, like
> bio_copy_from_iter(), and iov_iter_copy_from_user_atomic() . So,
> either those need to grow additional checks, or the hardened copy
> implementation is targeting single object copy use cases, not
> necessarily block-I/O. Yes, Kees, please advise.

The intention is mainly for copies that haven't had explicit bounds
checking already performed on them, yes. Is there something getting
checked out of the slab, or is it literally just the overhead of doing
the "is this slab?" check that you're seeing?

-- 
Kees Cook