linux-kernel - Re: [PATCH bpf-next v2 00/26] Resilient Queued Spin Lock

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Message-ID: <20250210093127.GD10324@noisy.programming.kicks-ass.net>
Date: Mon, 10 Feb 2025 10:31:27 +0100
From: Peter Zijlstra <peterz@...radead.org>
To: Kumar Kartikeya Dwivedi <memxor@...il.com>
Cc: bpf@...r.kernel.org, linux-kernel@...r.kernel.org,
	Linus Torvalds <torvalds@...ux-foundation.org>,
	Will Deacon <will@...nel.org>, Waiman Long <llong@...hat.com>,
	Alexei Starovoitov <ast@...nel.org>,
	Andrii Nakryiko <andrii@...nel.org>,
	Daniel Borkmann <daniel@...earbox.net>,
	Martin KaFai Lau <martin.lau@...nel.org>,
	Eduard Zingerman <eddyz87@...il.com>,
	"Paul E. McKenney" <paulmck@...nel.org>, Tejun Heo <tj@...nel.org>,
	Barret Rhoden <brho@...gle.com>, Josh Don <joshdon@...gle.com>,
	Dohyun Kim <dohyunkim@...gle.com>,
	linux-arm-kernel@...ts.infradead.org, kernel-team@...a.com
Subject: Re: [PATCH bpf-next v2 00/26] Resilient Queued Spin Lock

On Thu, Feb 06, 2025 at 02:54:08AM -0800, Kumar Kartikeya Dwivedi wrote:

> Additionally, eBPF programs attached to different parts of the kernel
> can introduce new control flow into the kernel, which increases the
> likelihood of deadlocks in code not written to handle reentrancy. There
> have been multiple syzbot reports surfacing deadlocks in internal kernel
> code due to the diverse ways in which eBPF programs can be attached to
> different parts of the kernel.  By switching the BPF subsystem’s lock
> usage to rqspinlock, all of these issues can be mitigated at runtime.

Only if the called stuff is using this new lock. IIRC we've had a number
of cases where eBPF was used to tie together 'normal' kernel functions
in a way that wasn't sound. You can't help there.

As an example, eBPF calling strncpy_from_user(), which ends up in fault
injection and badness happens -- this has been since fixed, but still.