linux-kernel - Re: [PATCH] perf: check branch sampling priv level in generic code

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Date:	Tue, 21 May 2013 13:08:58 +0200
From:	Peter Zijlstra <peterz@...radead.org>
To:	Stephane Eranian <eranian@...gle.com>
Cc:	linux-kernel@...r.kernel.org, mingo@...e.hu, ak@...ux.intel.com,
	jolsa@...hat.com
Subject: Re: [PATCH] perf: check branch sampling priv level in generic code

On Tue, May 21, 2013 at 12:53:37PM +0200, Stephane Eranian wrote:
> 
> This patch reverts commit 7cc23cd:
>  perf/x86/intel/lbr: Demand proper privileges for PERF_SAMPLE_BRANCH_KERNEL
> 
> The check is now implemented in generic code
> instead of x86 specific code. That way we
> do not have to repeat the test in each arch
> supporting branch sampling.

Good point indeed.

> Signed-off-by: Stephane Eranian <eranian@...gle.com>
> ---
>  arch/x86/kernel/cpu/perf_event_intel_lbr.c |   13 +++----------
>  kernel/events/core.c                       |    9 ++++-----
>  2 files changed, 7 insertions(+), 15 deletions(-)
> 

> diff --git a/kernel/events/core.c b/kernel/events/core.c
> index 9dc297f..cf79c81 100644
> --- a/kernel/events/core.c
> +++ b/kernel/events/core.c
> @@ -6327,11 +6327,6 @@ static int perf_copy_attr(struct perf_event_attr __user *uattr,
>  		if (!(mask & ~PERF_SAMPLE_BRANCH_PLM_ALL))
>  			return -EINVAL;
>  
> -		/* kernel level capture: check permissions */
> -		if ((mask & PERF_SAMPLE_BRANCH_PERM_PLM)
> -		    && perf_paranoid_kernel() && !capable(CAP_SYS_ADMIN))
> -			return -EACCES;
> -

Oh hey, there was a check.. 

>  		/* propagate priv level, when not set for branch */
>  		if (!(mask & PERF_SAMPLE_BRANCH_PLM_ALL)) {
>  
> @@ -6349,6 +6344,10 @@ static int perf_copy_attr(struct perf_event_attr __user *uattr,
>  			 */
>  			attr->branch_sample_type = mask;
>  		}
> +		/* kernel level capture: check permissions */
> +		if ((mask & PERF_SAMPLE_BRANCH_KERNEL)
> +		    && perf_paranoid_kernel() && !capable(CAP_SYS_ADMIN))
> +			return -EACCES;
>  	}
>  
>  	if (attr->sample_type & PERF_SAMPLE_REGS_USER) {
> -- 
> 1.7.9.5
> 
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