Re: [GIT PULL] usercopy whitelisting for v4.15-rc1

From: Kees Cook
Date: Fri Nov 17 2017 - 15:38:41 EST

On Fri, Nov 17, 2017 at 9:45 AM, Paolo Bonzini <pbonzini@xxxxxxxxxx> wrote:
> On 17/11/2017 18:35, Linus Torvalds wrote:
>> Honestly, I'm unlikely to pull this at all this merge window, simply
>> because I won't have time for it. This merge window is not going to be
>> one where I can take a leisurely look at something like this.
>> If you can make a smaller pull request that introduces the
>> infrastructure, but that _obviously_ cannot actually break anything,
>> that would be more likely to be palatable.
> As someone that was actually bitten by this stuff, and had a closer look
> at the usercopy whitelisting stuff... This one is really fail-fast
> (oopses all around if you forget to patch something), and with hardly

This is why I introduced the fallback mode: with both kvm and sctp
(ipv6) not noticed until late in the development cycle, I became much
less satisfied it had gotten sufficient testing. I wanted to make sure
there was a way for the series to land without actually breaking
things due to any missed whitelists.

> any configuration dependency. It's certainly a lot less scary to me
> than the GCC plugin stuff.

Agreed: this is a different type of change entirely. The GCC plugins
tend to be pretty invasive and non-discoverable. I prefer stuff like
this series, which is all visible in the code.

> But I don't want to ruin your Thanksgiving, so if Kees and/or you choose
> not to do this pull request---please do pull a subset, even after -rc1.
> It's easy enough to drop the final patch that changes whitelisting to
> blacklisting, and it'd be one less series bouncing around and touching
> files in several subsystems.

With the fallback mode, missed whitelists generate a WARN and are
allowed, so this series effectively only introduces tight controls on
the places where a whitelist is specifically introduced. And I went to
great lengths to document each whitelist usage in the commit logs.

I would agree it would be nice to get at least a subset of this in,
though. Linus, what would make you most comfortable?


Kees Cook
Pixel Security