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Date:   Wed, 29 Jan 2020 08:18:04 +1100 (AEDT)
From:   James Morris <jmorris@namei.org>
To:     Alexey Budankov <alexey.budankov@linux.intel.com>
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Subject: Re: [PATCH v6 09/10] drivers/perf: open access for CAP_PERFMON
 privileged process
In-Reply-To: <f2877038-da53-f981-4ddb-4e6c1c27c60f@linux.intel.com>
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References: <74d524ab-ac11-a7b8-1052-eba10f117e09@linux.intel.com> <f2877038-da53-f981-4ddb-4e6c1c27c60f@linux.intel.com>
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On Tue, 28 Jan 2020, Alexey Budankov wrote:

> 
> Open access to monitoring for CAP_PERFMON privileged process.
> Providing the access under CAP_PERFMON capability singly, without the
> rest of CAP_SYS_ADMIN credentials, excludes chances to misuse the
> credentials and makes operation more secure.
> 
> CAP_PERFMON implements the principal of least privilege for performance
> monitoring and observability operations (POSIX IEEE 1003.1e 2.2.2.39 principle
> of least privilege: A security design principle that states that a process
> or program be granted only those privileges (e.g., capabilities) necessary
> to accomplish its legitimate function, and only for the time that such
> privileges are actually required)
> 
> For backward compatibility reasons access to the monitoring remains open
> for CAP_SYS_ADMIN privileged processes but CAP_SYS_ADMIN usage for secure
> monitoring is discouraged with respect to CAP_PERFMON capability.
> 
> Signed-off-by: Alexey Budankov <alexey.budankov@linux.intel.com>
> ---
>  drivers/perf/arm_spe_pmu.c | 4 ++--
>  1 file changed, 2 insertions(+), 2 deletions(-)
> 


Acked-by: James Morris <jamorris@linux.microsoft.com>


> diff --git a/drivers/perf/arm_spe_pmu.c b/drivers/perf/arm_spe_pmu.c
> index 4e4984a55cd1..5dff81bc3324 100644
> --- a/drivers/perf/arm_spe_pmu.c
> +++ b/drivers/perf/arm_spe_pmu.c
> @@ -274,7 +274,7 @@ static u64 arm_spe_event_to_pmscr(struct perf_event *event)
>  	if (!attr->exclude_kernel)
>  		reg |= BIT(SYS_PMSCR_EL1_E1SPE_SHIFT);
>  
> -	if (IS_ENABLED(CONFIG_PID_IN_CONTEXTIDR) && capable(CAP_SYS_ADMIN))
> +	if (IS_ENABLED(CONFIG_PID_IN_CONTEXTIDR) && perfmon_capable())
>  		reg |= BIT(SYS_PMSCR_EL1_CX_SHIFT);
>  
>  	return reg;
> @@ -700,7 +700,7 @@ static int arm_spe_pmu_event_init(struct perf_event *event)
>  		return -EOPNOTSUPP;
>  
>  	reg = arm_spe_event_to_pmscr(event);
> -	if (!capable(CAP_SYS_ADMIN) &&
> +	if (!perfmon_capable() &&
>  	    (reg & (BIT(SYS_PMSCR_EL1_PA_SHIFT) |
>  		    BIT(SYS_PMSCR_EL1_CX_SHIFT) |
>  		    BIT(SYS_PMSCR_EL1_PCT_SHIFT))))
> 

-- 
James Morris
<jmorris@namei.org>