From: Linus Torvalds <torvalds@linux-foundation.org>
To: Dan Williams <dan.j.williams@intel.com>
Cc: Christoph Hellwig <hch@lst.de>, Linux MM <linux-mm@kvack.org>,
Jan Kara <jack@suse.cz>, Arnd Bergmann <arnd@arndb.de>,
"linux-nvdimm@lists.01.org" <linux-nvdimm@lists.01.org>,
Linux API <linux-api@vger.kernel.org>,
Andy Lutomirski <luto@kernel.org>,
Andrew Morton <akpm@linux-foundation.org>
Subject: Re: [PATCH 2/2] mm: introduce MAP_VALIDATE, a mechanism for for safely defining new mmap flags
Date: Thu, 31 Aug 2017 18:27:31 -0700 [thread overview]
Message-ID: <CA+55aFwsfUj1f41w8hqt9LN3-ajmJ=2AB1Nb6ZzwHgE1OKxGOw@mail.gmail.com> (raw)
In-Reply-To: <CAPcyv4jvTB4Aiei1-fGybyJNopXQy9zADpnFcuRNdZCS4Mf1QQ@mail.gmail.com>
On Thu, Aug 31, 2017 at 6:01 PM, Dan Williams <dan.j.williams@intel.com> wrote:
>
> Ugh, nommu defeats the MAP_SHARED_VALIDATE proposal from Linus.
>
> if ((flags & MAP_TYPE) != MAP_PRIVATE &&
> (flags & MAP_TYPE) != MAP_SHARED)
> return -EINVAL;
>
> ...parisc strikes again.
Why? That's no different from the case statement for the mmu case,
just written differently.
You *want* existing kernels to fail, since they don't test the bits
you want to test.
So you just want to rewrite these all as
switch (flags & MAP_TYPE) {
case MAP_SHARED_VALIDATE:
.. validate the other bits...
/* fallhtough */
case MAP_SHARED:
.. do the shared case ..
case MAP_PRIVATE:
.. do the private case ..
default:
return -EINVAL;
}
and you're all good.
I'm not seeing the problem.
Of course, I also suspect that for nommu you might as well just always
return -EINVAL anyway. The only people who would ever use
MAP_SHARED_VALIDATE are the kinds of people who do things that just
aren't likely relevant on nommu, but whatever..
Linus
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next prev parent reply other threads:[~2017-09-01 1:27 UTC|newest]
Thread overview: 12+ messages / expand[flat|nested] mbox.gz Atom feed top
2017-08-30 23:08 [PATCH 0/2] MAP_VALIDATE and mmap flags validation Dan Williams
2017-08-30 23:08 ` [PATCH 1/2] vfs: add flags parameter to ->mmap() in 'struct file_operations' Dan Williams
2017-08-31 10:02 ` Christoph Hellwig
2017-09-01 0:54 ` Dan Williams
2017-08-30 23:08 ` [PATCH 2/2] mm: introduce MAP_VALIDATE, a mechanism for for safely defining new mmap flags Dan Williams
2017-08-31 10:03 ` Christoph Hellwig
2017-09-01 1:01 ` Dan Williams
2017-09-01 1:27 ` Linus Torvalds [this message]
2017-09-01 1:40 ` Dan Williams
2017-09-01 7:34 ` Christoph Hellwig
2017-08-31 16:49 ` Linus Torvalds
2017-08-31 21:31 ` Dan Williams
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