linux-kernel - Re: [PATCH v2 5/7] rust: file: add `Kuid` wrapper

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Message-ID: <20231208204501.GJ28727@noisy.programming.kicks-ass.net>
Date:   Fri, 8 Dec 2023 21:45:01 +0100
From:   Peter Zijlstra <peterz@...radead.org>
To:     Kees Cook <keescook@...omium.org>
Cc:     Miguel Ojeda <miguel.ojeda.sandonis@...il.com>,
        Alice Ryhl <aliceryhl@...gle.com>,
        Miguel Ojeda <ojeda@...nel.org>,
        Alex Gaynor <alex.gaynor@...il.com>,
        Wedson Almeida Filho <wedsonaf@...il.com>,
        Boqun Feng <boqun.feng@...il.com>, Gary Guo <gary@...yguo.net>,
        Björn Roy Baron <bjorn3_gh@...tonmail.com>,
        Benno Lossin <benno.lossin@...ton.me>,
        Andreas Hindborg <a.hindborg@...sung.com>,
        Alexander Viro <viro@...iv.linux.org.uk>,
        Christian Brauner <brauner@...nel.org>,
        Greg Kroah-Hartman <gregkh@...uxfoundation.org>,
        Arve Hjønnevåg <arve@...roid.com>,
        Todd Kjos <tkjos@...roid.com>,
        Martijn Coenen <maco@...roid.com>,
        Joel Fernandes <joel@...lfernandes.org>,
        Carlos Llamas <cmllamas@...gle.com>,
        Suren Baghdasaryan <surenb@...gle.com>,
        Dan Williams <dan.j.williams@...el.com>,
        Matthew Wilcox <willy@...radead.org>,
        Thomas Gleixner <tglx@...utronix.de>,
        Daniel Xu <dxu@...uu.xyz>, linux-kernel@...r.kernel.org,
        rust-for-linux@...r.kernel.org, linux-fsdevel@...r.kernel.org
Subject: Re: [PATCH v2 5/7] rust: file: add `Kuid` wrapper

On Fri, Dec 08, 2023 at 10:18:47AM -0800, Kees Cook wrote:

> Even if we look at the prerequisites for mounting an attack here, we've
> already got things in place to help mitigate arbitrary code execution
> (KCFI, BTI, etc). Nothing is perfect, but speculation gadgets are
> pretty far down on the list of concerns, IMO. We have no real x86 ROP
> defense right now in the kernel, so that's a much lower hanging fruit
> for attackers.

Supervisor shadow stacks, as they exist today, just can't work on Linux.
Should get fixed with FRED, but yeah, this is all somewhat unfortunate.

> As another comparison, on x86 there are so many direct execution gadgets
> present in middle-of-instruction code patterns that worrying about a
> speculation gadget seems silly to me.

FineIBT (or even IBT) limits the middle of function gadgets
significantly.