linux-kernel - Re: [PATCH v5 01/10] capabilities: introduce CAP

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Date:   Tue, 21 Jan 2020 09:43:49 -0500
From:   Stephen Smalley <sds@...ho.nsa.gov>
To:     Alexey Budankov <alexey.budankov@...ux.intel.com>,
        Peter Zijlstra <peterz@...radead.org>,
        Arnaldo Carvalho de Melo <acme@...nel.org>,
        Ingo Molnar <mingo@...hat.com>,
        "jani.nikula@...ux.intel.com" <jani.nikula@...ux.intel.com>,
        "joonas.lahtinen@...ux.intel.com" <joonas.lahtinen@...ux.intel.com>,
        "rodrigo.vivi@...el.com" <rodrigo.vivi@...el.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>,
        James Morris <jmorris@...ei.org>,
        Will Deacon <will.deacon@....com>,
        Mark Rutland <mark.rutland@....com>,
        Robert Richter <rric@...nel.org>,
        Alexei Starovoitov <ast@...nel.org>
Cc:     Jiri Olsa <jolsa@...hat.com>, Andi Kleen <ak@...ux.intel.com>,
        Stephane Eranian <eranian@...gle.com>,
        Igor Lubashev <ilubashe@...mai.com>,
        Alexander Shishkin <alexander.shishkin@...ux.intel.com>,
        Namhyung Kim <namhyung@...nel.org>,
        Song Liu <songliubraving@...com>,
        Lionel Landwerlin <lionel.g.landwerlin@...el.com>,
        Thomas Gleixner <tglx@...utronix.de>,
        linux-kernel <linux-kernel@...r.kernel.org>,
        "linux-security-module@...r.kernel.org" 
        <linux-security-module@...r.kernel.org>,
        "selinux@...r.kernel.org" <selinux@...r.kernel.org>,
        "intel-gfx@...ts.freedesktop.org" <intel-gfx@...ts.freedesktop.org>,
        "linux-parisc@...r.kernel.org" <linux-parisc@...r.kernel.org>,
        "linuxppc-dev@...ts.ozlabs.org" <linuxppc-dev@...ts.ozlabs.org>,
        linux-arm-kernel@...ts.infradead.org,
        "linux-perf-users@...r.kernel.org" <linux-perf-users@...r.kernel.org>,
        oprofile-list@...ts.sf.net
Subject: Re: [PATCH v5 01/10] capabilities: introduce CAP_PERFMON to kernel
 and user space

On 1/20/20 6:23 AM, Alexey Budankov wrote:
> 
> Introduce CAP_PERFMON capability designed to secure system performance
> monitoring and observability operations so that CAP_PERFMON would assist
> CAP_SYS_ADMIN capability in its governing role for perf_events, i915_perf
> and other performance monitoring and observability subsystems.
> 
> CAP_PERFMON intends to harden system security and integrity during system
> performance monitoring and observability operations by decreasing attack
> surface that is available to a CAP_SYS_ADMIN privileged process [1].
> Providing access to system performance monitoring and observability
> operations 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 intends to take over CAP_SYS_ADMIN credentials related to
> system performance monitoring and observability operations and balance
> amount of CAP_SYS_ADMIN credentials following the recommendations in the
> capabilities man page [1] for CAP_SYS_ADMIN: "Note: this capability is
> overloaded; see Notes to kernel developers, below."
> 
> Although the software running under CAP_PERFMON can not ensure avoidance
> of related hardware issues, the software can still mitigate these issues
> following the official embargoed hardware issues mitigation procedure [2].
> The bugs in the software itself could be fixed following the standard
> kernel development process [3] to maintain and harden security of system
> performance monitoring and observability operations.
> 
> [1] http://man7.org/linux/man-pages/man7/capabilities.7.html
> [2] https://www.kernel.org/doc/html/latest/process/embargoed-hardware-issues.html
> [3] https://www.kernel.org/doc/html/latest/admin-guide/security-bugs.html
> 
> Signed-off-by: Alexey Budankov <alexey.budankov@...ux.intel.com>
> ---
>   include/linux/capability.h          | 12 ++++++++++++
>   include/uapi/linux/capability.h     |  8 +++++++-
>   security/selinux/include/classmap.h |  4 ++--
>   3 files changed, 21 insertions(+), 3 deletions(-)
> 
> diff --git a/include/linux/capability.h b/include/linux/capability.h
> index ecce0f43c73a..8784969d91e1 100644
> --- a/include/linux/capability.h
> +++ b/include/linux/capability.h
> @@ -251,6 +251,18 @@ extern bool privileged_wrt_inode_uidgid(struct user_namespace *ns, const struct
>   extern bool capable_wrt_inode_uidgid(const struct inode *inode, int cap);
>   extern bool file_ns_capable(const struct file *file, struct user_namespace *ns, int cap);
>   extern bool ptracer_capable(struct task_struct *tsk, struct user_namespace *ns);
> +static inline bool perfmon_capable(void)
> +{
> +	struct user_namespace *ns = &init_user_ns;
> +
> +	if (ns_capable_noaudit(ns, CAP_PERFMON))
> +		return ns_capable(ns, CAP_PERFMON);
> +
> +	if (ns_capable_noaudit(ns, CAP_SYS_ADMIN))
> +		return ns_capable(ns, CAP_SYS_ADMIN);
> +
> +	return false;
> +}

Why _noaudit()?  Normally only used when a permission failure is 
non-fatal to the operation.  Otherwise, we want the audit message.