linux-kernel - Re: [PATCH v6 09/10] drivers/perf: open access for CAP

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Message-ID: <alpine.LRH.2.21.2001290817560.2204@namei.org>
Date:   Wed, 29 Jan 2020 08:18:04 +1100 (AEDT)
From:   James Morris <jmorris@...ei.org>
To:     Alexey Budankov <alexey.budankov@...ux.intel.com>
cc:     Peter Zijlstra <peterz@...radead.org>,
        Arnaldo Carvalho de Melo <acme@...nel.org>,
        Ingo Molnar <mingo@...hat.com>,
        "benh@...nel.crashing.org" <benh@...nel.crashing.org>,
        Paul Mackerras <paulus@...ba.org>,
        Michael Ellerman <mpe@...erman.id.au>,
        "james.bottomley@...senpartnership.com" 
        <james.bottomley@...senpartnership.com>,
        Serge Hallyn <serge@...lyn.com>, Will Deacon <will@...nel.org>,
        Robert Richter <rric@...nel.org>,
        Alexei Starovoitov <ast@...nel.org>,
        "intel-gfx@...ts.freedesktop.org" <intel-gfx@...ts.freedesktop.org>,
        Jiri Olsa <jolsa@...hat.com>, Andi Kleen <ak@...ux.intel.com>,
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        Igor Lubashev <ilubashe@...mai.com>,
        Alexander Shishkin <alexander.shishkin@...ux.intel.com>,
        Namhyung Kim <namhyung@...nel.org>,
        Song Liu <songliubraving@...com>,
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        linux-kernel <linux-kernel@...r.kernel.org>,
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        <linux-security-module@...r.kernel.org>,
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        linux-arm-kernel <linux-arm-kernel@...ts.infradead.org>,
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        oprofile-list@...ts.sf.net
Subject: Re: [PATCH v6 09/10] drivers/perf: open access for CAP_PERFMON
 privileged process

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@...ux.intel.com>
> ---
>  drivers/perf/arm_spe_pmu.c | 4 ++--
>  1 file changed, 2 insertions(+), 2 deletions(-)
> 


Acked-by: James Morris <jamorris@...ux.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@...ei.org>