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Date:   Wed, 8 Jan 2020 17:07:13 +0100
From:   Peter Zijlstra <peterz@infradead.org>
To:     Alexey Budankov <alexey.budankov@linux.intel.com>
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Subject: Re: [PATCH v4 2/9] perf/core: open access for CAP_SYS_PERFMON
 privileged process
Message-ID: <20200108160713.GI2844@hirez.programming.kicks-ass.net>
References: <c0460c78-b1a6-b5f7-7119-d97e5998f308@linux.intel.com>
 <c93309dc-b920-f5fa-f997-e8b2faf47b88@linux.intel.com>
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On Wed, Dec 18, 2019 at 12:25:35PM +0300, Alexey Budankov wrote:
> 
> Open access to perf_events monitoring for CAP_SYS_PERFMON privileged
> processes. For backward compatibility reasons access to perf_events
> subsystem remains open for CAP_SYS_ADMIN privileged processes but
> CAP_SYS_ADMIN usage for secure perf_events monitoring is discouraged
> with respect to CAP_SYS_PERFMON capability.
> 
> Signed-off-by: Alexey Budankov <alexey.budankov@linux.intel.com>
> ---
>  include/linux/perf_event.h | 6 +++---
>  kernel/events/core.c       | 6 +++---
>  2 files changed, 6 insertions(+), 6 deletions(-)
> 
> diff --git a/include/linux/perf_event.h b/include/linux/perf_event.h
> index 34c7c6910026..f46acd69425f 100644
> --- a/include/linux/perf_event.h
> +++ b/include/linux/perf_event.h
> @@ -1285,7 +1285,7 @@ static inline int perf_is_paranoid(void)
>  
>  static inline int perf_allow_kernel(struct perf_event_attr *attr)
>  {
> -	if (sysctl_perf_event_paranoid > 1 && !capable(CAP_SYS_ADMIN))
> +	if (sysctl_perf_event_paranoid > 1 && !perfmon_capable())
>  		return -EACCES;
>  
>  	return security_perf_event_open(attr, PERF_SECURITY_KERNEL);
> @@ -1293,7 +1293,7 @@ static inline int perf_allow_kernel(struct perf_event_attr *attr)
>  
>  static inline int perf_allow_cpu(struct perf_event_attr *attr)
>  {
> -	if (sysctl_perf_event_paranoid > 0 && !capable(CAP_SYS_ADMIN))
> +	if (sysctl_perf_event_paranoid > 0 && !perfmon_capable())
>  		return -EACCES;
>  
>  	return security_perf_event_open(attr, PERF_SECURITY_CPU);
> @@ -1301,7 +1301,7 @@ static inline int perf_allow_cpu(struct perf_event_attr *attr)
>  
>  static inline int perf_allow_tracepoint(struct perf_event_attr *attr)
>  {
> -	if (sysctl_perf_event_paranoid > -1 && !capable(CAP_SYS_ADMIN))
> +	if (sysctl_perf_event_paranoid > -1 && !perfmon_capable())
>  		return -EPERM;
>  
>  	return security_perf_event_open(attr, PERF_SECURITY_TRACEPOINT);

These are OK I suppose.

> diff --git a/kernel/events/core.c b/kernel/events/core.c
> index 059ee7116008..d9db414f2197 100644
> --- a/kernel/events/core.c
> +++ b/kernel/events/core.c
> @@ -9056,7 +9056,7 @@ static int perf_kprobe_event_init(struct perf_event *event)
>  	if (event->attr.type != perf_kprobe.type)
>  		return -ENOENT;
>  
> -	if (!capable(CAP_SYS_ADMIN))
> +	if (!perfmon_capable())
>  		return -EACCES;
>  
>  	/*

This one only allows attaching to already extant kprobes, right? It does
not allow creation of kprobes.

> @@ -9116,7 +9116,7 @@ static int perf_uprobe_event_init(struct perf_event *event)
>  	if (event->attr.type != perf_uprobe.type)
>  		return -ENOENT;
>  
> -	if (!capable(CAP_SYS_ADMIN))
> +	if (!perfmon_capable())
>  		return -EACCES;
>  
>  	/*

Idem, I presume.

> @@ -11157,7 +11157,7 @@ SYSCALL_DEFINE5(perf_event_open,
>  	}
>  
>  	if (attr.namespaces) {
> -		if (!capable(CAP_SYS_ADMIN))
> +		if (!perfmon_capable())
>  			return -EACCES;
>  	}

And given we basically make the entire kernel observable with this CAP,
busting namespaces shoulnd't be a problem either.

So yeah, I suppose that works.