linux-kernel - Re: [PATCH linux-next 2/2] perf: Return EACCESS when need perfmon capability

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Message-ID: <57627eec-10b5-4eb0-bfe2-f404a3492eee@linaro.org>
Date: Mon, 6 Jan 2025 15:59:43 +0000
From: James Clark <james.clark@...aro.org>
To: Luo Gengkun <luogengkun@...weicloud.com>
Cc: mingo@...hat.com, acme@...nel.org, namhyung@...nel.org,
 mark.rutland@....com, alexander.shishkin@...ux.intel.com, jolsa@...nel.org,
 irogers@...gle.com, adrian.hunter@...el.com, kan.liang@...ux.intel.com,
 tglx@...utronix.de, bp@...en8.de, dave.hansen@...ux.intel.com,
 x86@...nel.org, hpa@...or.com, will@...nel.org, paul@...l-moore.com,
 jmorris@...ei.org, serge@...lyn.com, rostedt@...dmis.org,
 mhiramat@...nel.org, mathieu.desnoyers@...icios.com,
 stephen.smalley.work@...il.com, omosnace@...hat.com,
 linux-perf-users@...r.kernel.org, linux-kernel@...r.kernel.org,
 linux-arm-kernel@...ts.infradead.org, linux-security-module@...r.kernel.org,
 linux-trace-kernel@...r.kernel.org, selinux@...r.kernel.org,
 Peter Zijlstra <peterz@...radead.org>
Subject: Re: [PATCH linux-next 2/2] perf: Return EACCESS when need perfmon
 capability



On 23/12/2024 7:06 am, Luo Gengkun wrote:
> For perf_allow_kernel and perf_allow_cpu, both return EACCES when require
> CAP_PERFMON or CAP_SYS_ADMIN permissions, so update perf_allow_tracepoint
> to keep them the same.
> 
> Signed-off-by: Luo Gengkun <luogengkun@...weicloud.com>
> ---
>   include/linux/perf_event.h | 2 +-
>   1 file changed, 1 insertion(+), 1 deletion(-)
> 
> diff --git a/include/linux/perf_event.h b/include/linux/perf_event.h
> index 5d2ec4283ebf..c1bc0d7a275b 100644
> --- a/include/linux/perf_event.h
> +++ b/include/linux/perf_event.h
> @@ -1685,7 +1685,7 @@ static inline int perf_allow_cpu(void)
>   static inline int perf_allow_tracepoint(void)
>   {
>   	if (sysctl_perf_event_paranoid > -1 && !perfmon_capable())
> -		return -EPERM;
> +		return -EACCES;
>   

Is this necessary other than for consistency? If not it might be best to 
leave it inconsistent even if it's wrong. I see quite a few "if EPERM do 
this..." type things in Perf, so changing this would break error 
messages being shown to users.

If anything, EPERM seems more correct because EACCESS is more about file 
access.

Thanks
James