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

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Message-ID: <CAGXu5jL=aowLRbn1QQaSXuSvmJrKos0msSXCmU18kqTRjy2gPA@mail.gmail.com>
Date:   Fri, 17 Nov 2017 12:35:28 -0800
From:   Kees Cook <keescook@...omium.org>
To:     Linus Torvalds <torvalds@...ux-foundation.org>,
        Paolo Bonzini <pbonzini@...hat.com>
Cc:     David Windsor <dave@...lcore.net>,
        Linux Kernel Mailing List <linux-kernel@...r.kernel.org>
Subject: Re: [GIT PULL] usercopy whitelisting for v4.15-rc1

On Fri, Nov 17, 2017 at 9:45 AM, Paolo Bonzini <pbonzini@...hat.com> 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

-- 
Kees Cook
Pixel Security