linux-kernel - Re: [PATCH] x86/ibt: Implement FineIBT

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Date:   Tue, 18 Oct 2022 22:05:03 +0200
From:   Peter Zijlstra <peterz@...radead.org>
To:     Kees Cook <keescook@...omium.org>
Cc:     x86@...nel.org, Sami Tolvanen <samitolvanen@...gle.com>,
        Joao Moreira <joao@...rdrivepizza.com>,
        linux-kernel@...r.kernel.org, Mark Rutland <mark.rutland@....com>,
        Josh Poimboeuf <jpoimboe@...hat.com>
Subject: Re: [PATCH] x86/ibt: Implement FineIBT

On Tue, Oct 18, 2022 at 11:09:13AM -0700, Kees Cook wrote:
> I still think it's worth noting it does technically weaken the
> "attacker-controlled executable memory content injection" attack
> requirements, too. While an attacker needs to make sure they place an
> ENDBR at the start of their injected code, they no longer need to also
> learn and inject the CFI hash too, as the malicious code can just not
> do the check at all. The difference in protection currently isn't much.

Hmm, true; although I do feel that the moment attackers can write code
we might be having worse problems.

> It's not a very difficult requirement to get attacker-controlled bytes
> into executable memory, as there are already existing APIs that provide
> this to varying degrees of reachability, utility, and discoverability --
> for example, BPF JIT when constant blinding isn't enabled (the unfortunate
> default). 

BPF has another problem in that the current control transfer to BPF
progs is nocfi. At the very least we can have them have a hash, no?