linux-hardening - Re: [PATCH bpf-next v5 08/12] bpf: Report rqspinlock deadlocks/timeout to BPF stderr

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Message-ID: <202507301559.C832A9C@keescook>
Date: Wed, 30 Jul 2025 16:02:12 -0700
From: Kees Cook <kees@...nel.org>
To: Kumar Kartikeya Dwivedi <memxor@...il.com>
Cc: bpf@...r.kernel.org, Emil Tsalapatis <emil@...alapatis.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>,
	Barret Rhoden <brho@...gle.com>,
	Matt Bobrowski <mattbobrowski@...gle.com>, kkd@...a.com,
	kernel-team@...a.com, linux-hardening@...r.kernel.org
Subject: Re: [PATCH bpf-next v5 08/12] bpf: Report rqspinlock
 deadlocks/timeout to BPF stderr

On Thu, Jul 03, 2025 at 01:48:14PM -0700, Kumar Kartikeya Dwivedi wrote:
> +static void bpf_prog_report_rqspinlock_violation(const char *str, void *lock, bool irqsave)
> +{
> +	struct rqspinlock_held *rqh = this_cpu_ptr(&rqspinlock_held_locks);
> +	struct bpf_stream_stage ss;
> +	struct bpf_prog *prog;
> +
> +	prog = bpf_prog_find_from_stack();
> +	if (!prog)
> +		return;
> +	bpf_stream_stage(ss, prog, BPF_STDERR, ({
> +		bpf_stream_printk(ss, "ERROR: %s for bpf_res_spin_lock%s\n", str, irqsave ? "_irqsave" : "");
> +		bpf_stream_printk(ss, "Attempted lock   = 0x%px\n", lock);
> +		bpf_stream_printk(ss, "Total held locks = %d\n", rqh->cnt);
> +		for (int i = 0; i < min(RES_NR_HELD, rqh->cnt); i++)
> +			bpf_stream_printk(ss, "Held lock[%2d] = 0x%px\n", i, rqh->locks[i]);
> +		bpf_stream_dump_stack(ss);

Please don't include %px in stuff going back to userspace in standard
error reporting. That's a kernel address leak:
https://docs.kernel.org/process/deprecated.html#p-format-specifier

I don't see any justification here, please remove the lock address or
use regular %p to get a hashed value.

-- 
Kees Cook