Date:	Fri, 10 Jun 2011 13:19:32 +0200
From:	Ingo Molnar <mingo@...e.hu>
To:	pageexec@...email.hu
Cc:	Linus Torvalds <torvalds@...ux-foundation.org>,
	Andi Kleen <andi@...stfloor.org>,
	Andy Lutomirski <luto@....edu>, x86@...nel.org,
	Thomas Gleixner <tglx@...utronix.de>,
	linux-kernel@...r.kernel.org, Jesper Juhl <jj@...osbits.net>,
	Borislav Petkov <bp@...en8.de>,
	Andrew Morton <akpm@...ux-foundation.org>,
	Arjan van de Ven <arjan@...radead.org>,
	Jan Beulich <JBeulich@...ell.com>,
	richard -rw- weinberger <richard.weinberger@...il.com>,
	Mikael Pettersson <mikpe@...uu.se>,
	Brian Gerst <brgerst@...il.com>,
	Louis Rilling <Louis.Rilling@...labs.com>,
	Valdis.Kletnieks@...edu
Subject: Re: [PATCH v5 9/9] x86-64: Add CONFIG_UNSAFE_VSYSCALLS to
 feature-removal-schedule


* pageexec@...email.hu <pageexec@...email.hu> wrote:

> let me tell you now a real distadvantage of your coverup: [...]

Our opinion is that the scheme you are suggesting is flawed and 
reduces security, so we refuse to use it. That is not a 'coverup', to 
the contrary, it *helps* security - see below.

> [...] you're hurting the good guys (the defenders) a lot more than 
> you're hurting the bad guys (the attackers). why? because of the 
> usual asymmetry of the situation we often face in security. an 
> attacker needs to find only a single commit silently fixing a 
> security bug (never mind finding the earlier commit that introduced 
> it) whereas the defenders would have to find all of them.
> 
> thanks to your policy you can guess which side has a distinct 
> advantage from the start and how well the other side fares.

Firstly, the assymetry is fundamental: attackers *always* have an 
easier way destroying stuff than the good guys are at building new 
things. This is the second law of thermodynamics.

Secondly, you are missing one fundamental aspect: the 'good guys' are 
not just the 'defenders'. The good guys are a *much* broader group of 
people: the 'bug fixers'.

Thirdly, you never replied in substance to our arguments that CVE 
numbers are woefully inadequate: they miss the majority of bugs that 
can have a security impact. In fact i argue that the way software is 
written and fixed today it's not possible to effectively map out 
'bugs with a security impact' at all: pretty much *any* bug that 
modifies the kernel image can have a security impact. Bug fixers are 
not at all concentrated on thinking like parasitic attackers, so 
security side effects often remain undiscovered. Why pretend we have 
a list of CVEs when we know that it's only fake?

Fourth, exactly how does putting CVE numbers make it harder for 
attackers? It makes it distinctly *easier*: people will update their 
systems based on a list of say 10 CVEs that affect them, totally 
blind to the 100+ other bugs that may (or may not) have an effect on 
them. An attacker will now only have to find an *already fixed* bug 
that has a security impact and which didn't get a CVE and attack a 
large body of systems that people think are safe.

With the current upstream kernel policy we do not deceive users: we 
say that the way to be most secure is to be uptodate. Attackers will 
have to find an entirely new, not yet fixed security hole, instead of 
just a bug that missed the CVE filter ...

I.e. our opinion is, on very good and honest grounds, that your 
scheme creates a false sense of security and actually harms real 
security and we simply refuse to support such a scheme.

Thanks,

	Ingo
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