From: Kees Cook <kees@kernel.org>
To: Alexei Starovoitov <alexei.starovoitov@gmail.com>
Cc: Kumar Kartikeya Dwivedi <memxor@gmail.com>,
bpf <bpf@vger.kernel.org>, Emil Tsalapatis <emil@etsalapatis.com>,
Alexei Starovoitov <ast@kernel.org>,
Andrii Nakryiko <andrii@kernel.org>,
Daniel Borkmann <daniel@iogearbox.net>,
Martin KaFai Lau <martin.lau@kernel.org>,
Eduard Zingerman <eddyz87@gmail.com>,
Barret Rhoden <brho@google.com>,
Matt Bobrowski <mattbobrowski@google.com>,
kkd@meta.com, Kernel Team <kernel-team@meta.com>,
linux-hardening@vger.kernel.org
Subject: Re: [PATCH bpf-next v5 08/12] bpf: Report rqspinlock deadlocks/timeout to BPF stderr
Date: Wed, 30 Jul 2025 16:19:23 -0700 [thread overview]
Message-ID: <202507301618.ABE8A9BB23@keescook> (raw)
In-Reply-To: <CAADnVQLbgXxUROzhKhdK8v+2Z4f5nqV34rHMn2Q0PebUo+VqyQ@mail.gmail.com>
On Wed, Jul 30, 2025 at 04:13:25PM -0700, Alexei Starovoitov wrote:
> On Wed, Jul 30, 2025 at 4:09 PM Kees Cook <kees@kernel.org> wrote:
> >
> > On Wed, Jul 30, 2025 at 04:07:33PM -0700, Alexei Starovoitov wrote:
> > > On Wed, Jul 30, 2025 at 4:02 PM Kees Cook <kees@kernel.org> wrote:
> > > >
> > > > 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.
> > >
> > > There is no leak here.
> > > The prog was loaded by root and error is read by root.
> >
> > uid has nothing to do with it. Leaking addresses needs the right
> > capability set. Is that always true here?
>
> yes. For bpf prog to use this kfunc it needs CAP_BPF and CAP_PERMON.
> What's allowed under them is described in include/uapi/linux/capability.h
Okay, thanks! That wasn't detailed in the commit log (for folks like me
with less familiarity with BPF), so I just got worried when I saw
"stderr" mentioned. :)
--
Kees Cook
next prev parent reply other threads:[~2025-07-30 23:19 UTC|newest]
Thread overview: 19+ messages / expand[flat|nested] mbox.gz Atom feed top
2025-07-03 20:48 [PATCH bpf-next v5 00/12] BPF Standard Streams Kumar Kartikeya Dwivedi
2025-07-03 20:48 ` [PATCH bpf-next v5 01/12] bpf: Refactor bprintf buffer support Kumar Kartikeya Dwivedi
2025-07-03 20:48 ` [PATCH bpf-next v5 02/12] bpf: Introduce BPF standard streams Kumar Kartikeya Dwivedi
2025-07-03 20:48 ` [PATCH bpf-next v5 03/12] bpf: Add function to extract program source info Kumar Kartikeya Dwivedi
2025-07-03 20:48 ` [PATCH bpf-next v5 04/12] bpf: Ensure RCU lock is held around bpf_prog_ksym_find Kumar Kartikeya Dwivedi
2025-07-03 20:48 ` [PATCH bpf-next v5 05/12] bpf: Add function to find program from stack trace Kumar Kartikeya Dwivedi
2025-07-03 20:48 ` [PATCH bpf-next v5 06/12] bpf: Add dump_stack() analogue to print to BPF stderr Kumar Kartikeya Dwivedi
2025-07-03 20:48 ` [PATCH bpf-next v5 07/12] bpf: Report may_goto timeout " Kumar Kartikeya Dwivedi
2025-07-03 20:48 ` [PATCH bpf-next v5 08/12] bpf: Report rqspinlock deadlocks/timeout " Kumar Kartikeya Dwivedi
2025-07-30 23:02 ` Kees Cook
2025-07-30 23:07 ` Alexei Starovoitov
2025-07-30 23:09 ` Kees Cook
2025-07-30 23:13 ` Alexei Starovoitov
2025-07-30 23:19 ` Kees Cook [this message]
2025-07-03 20:48 ` [PATCH bpf-next v5 09/12] libbpf: Add bpf_stream_printk() macro Kumar Kartikeya Dwivedi
2025-07-03 20:48 ` [PATCH bpf-next v5 10/12] libbpf: Introduce bpf_prog_stream_read() API Kumar Kartikeya Dwivedi
2025-07-03 20:48 ` [PATCH bpf-next v5 11/12] bpftool: Add support for dumping streams Kumar Kartikeya Dwivedi
2025-07-03 20:48 ` [PATCH bpf-next v5 12/12] selftests/bpf: Add tests for prog streams Kumar Kartikeya Dwivedi
2025-07-04 2:40 ` [PATCH bpf-next v5 00/12] BPF Standard Streams patchwork-bot+netdevbpf
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