linux-kernel - Re: [PATCH v1 1/1] bpf: Mark BPF printing functions with _

lists.openwall.net		lists / announce owl-users owl-dev john-users john-dev passwdqc-users yescrypt popa3d-users / oss-security kernel-hardening musl sabotage tlsify passwords / crypt-dev xvendor / Bugtraq Full-Disclosure linux-kernel linux-netdev linux-ext4 linux-hardening linux-cve-announce PHC
Open Source and information security mailing list archives

Hash Suite: Windows password security audit tool. GUI, reports in PDF.

[<prev] [next>] [<thread-prev] [thread-next>] [day] [month] [year] [list]

Message-ID: <aTgl_bjO1O9Ddpmv@smile.fi.intel.com>
Date: Tue, 9 Dec 2025 15:37:45 +0200
From: Andy Shevchenko <andriy.shevchenko@...ux.intel.com>
To: Alexei Starovoitov <alexei.starovoitov@...il.com>
Cc: Alexei Starovoitov <ast@...nel.org>, bpf <bpf@...r.kernel.org>,
	LKML <linux-kernel@...r.kernel.org>,
	linux-trace-kernel <linux-trace-kernel@...r.kernel.org>,
	Daniel Borkmann <daniel@...earbox.net>,
	John Fastabend <john.fastabend@...il.com>,
	Andrii Nakryiko <andrii@...nel.org>,
	Martin KaFai Lau <martin.lau@...ux.dev>,
	Eduard Zingerman <eddyz87@...il.com>, Song Liu <song@...nel.org>,
	Yonghong Song <yonghong.song@...ux.dev>,
	KP Singh <kpsingh@...nel.org>, Stanislav Fomichev <sdf@...ichev.me>,
	Hao Luo <haoluo@...gle.com>, Jiri Olsa <jolsa@...nel.org>,
	Matt Bobrowski <mattbobrowski@...gle.com>,
	Steven Rostedt <rostedt@...dmis.org>,
	Masami Hiramatsu <mhiramat@...nel.org>,
	Mathieu Desnoyers <mathieu.desnoyers@...icios.com>,
	Alan Maguire <alan.maguire@...cle.com>,
	kernel test robot <lkp@...el.com>
Subject: Re: [PATCH v1 1/1] bpf: Mark BPF printing functions with __printf()
 attribute

On Tue, Dec 09, 2025 at 06:12:46PM +0900, Alexei Starovoitov wrote:
> On Tue, Dec 9, 2025 at 1:21 AM Andy Shevchenko
> <andriy.shevchenko@...ux.intel.com> wrote:
> >
> > The printing functions in BPF code are using printf() type of format,
> > and compiler is not happy about them as is:
> >
> > kernel/bpf/helpers.c:1069:9: error: function ‘____bpf_snprintf’ might be a candidate for ‘gnu_printf’ format attribute [-Werror=suggest-attribute=format]
> >  1069 |         err = bstr_printf(str, str_size, fmt, data.bin_args);
> >       |         ^~~
> >
> > kernel/trace/bpf_trace.c:377:9: error: function ‘____bpf_trace_printk’ might be a candidate for ‘gnu_printf’ format attribute [-Werror=suggest-attribute=format]
> >   377 |         ret = bstr_printf(data.buf, MAX_BPRINTF_BUF, fmt, data.bin_args);
> >       |         ^~~
> >
> > kernel/trace/bpf_trace.c:433:9: error: function ‘____bpf_trace_vprintk’ might be a candidate for ‘gnu_printf’ format attribute [-Werror=suggest-attribute=format]
> >   433 |         ret = bstr_printf(data.buf, MAX_BPRINTF_BUF, fmt, data.bin_args);
> >       |         ^~~
> >
> > kernel/trace/bpf_trace.c:475:9: error: function ‘____bpf_seq_printf’ might be a candidate for ‘gnu_printf’ format attribute [-Werror=suggest-attribute=format]
> >   475 |         seq_bprintf(m, fmt, data.bin_args);
> >       |         ^~~~~~~~~~~
> >
> > Fix the compilation errors by adding __printf() attribute. For that
> > we need to pass it down to the BPF_CALL_x() and wrap into PRINTF_BPF_CALL_*()
> > to make code neater.

> This is pointless churn to shut up a warning.

In some cases, like mine, it's an error.

> Teach syzbot to stop this spam instead.

It prevents to perform `make W=1` builds with the default CONFIG_WERROR,
which is 'y'.

> At the end this patch doesn't make any visible difference,
> since user declarations of these helpers are auto generated
> from uapi/bpf.h file and __printf attribute is not there.

I see, thanks for the review.
Any recommendations on how to fix this properly?

-- 
With Best Regards,
Andy Shevchenko