Re: [PATCH] x86/ibt: Implement FineIBT

From: Peter Zijlstra <peterz@infradead.org>
To: Kees Cook <keescook@chromium.org>
Cc: x86@kernel.org, Sami Tolvanen <samitolvanen@google.com>,
	Joao Moreira <joao@overdrivepizza.com>,
	linux-kernel@vger.kernel.org, Mark Rutland <mark.rutland@arm.com>,
	Josh Poimboeuf <jpoimboe@redhat.com>
Subject: Re: [PATCH] x86/ibt: Implement FineIBT
Date: Tue, 18 Oct 2022 22:05:03 +0200	[thread overview]
Message-ID: <Y08G73HOddpS40ny@hirez.programming.kicks-ass.net> (raw)
In-Reply-To: <202210181020.79AF7F7@keescook>

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?