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From:   Alexey Budankov <alexey.budankov@linux.intel.com>
Subject: Re: [PATCH v7 00/12] Introduce CAP_PERFMON to secure system
 performance monitoring and observability
To:     James Morris <jmorris@namei.org>, Serge Hallyn <serge@hallyn.com>,
        Stephen Smalley <sds@tycho.nsa.gov>,
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        Alexei Starovoitov <ast@kernel.org>,
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Date:   Tue, 25 Feb 2020 12:55:54 +0300
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Hi,

Is there anything else I could do in order to move the changes forward
or is something still missing from this patch set?
Could you please share you mind?

Thanks,
Alexey

On 17.02.2020 11:02, Alexey Budankov wrote:
> 
> Currently access to perf_events, i915_perf and other performance
> monitoring and observability subsystems of the kernel is open only for
> a privileged process [1] with CAP_SYS_ADMIN capability enabled in the
> process effective set [2].
> 
> This patch set introduces 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 performance monitoring and observability subsystems of the kernel.
> 
> CAP_PERFMON intends to harden system security and integrity during
> performance monitoring and observability operations by decreasing attack
> surface that is available to a CAP_SYS_ADMIN privileged process [2].
> Providing the access to 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 the operation more secure. Thus, 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)
> 
> CAP_PERFMON intends to meet the demand to secure system performance
> monitoring and observability operations for adoption in security
> sensitive, restricted, multiuser production environments (e.g. HPC
> clusters, cloud and virtual compute environments), where root or
> CAP_SYS_ADMIN credentials are not available to mass users of a system,
> and securely unblock accessibility of system performance monitoring and
> observability operations beyond root and CAP_SYS_ADMIN use cases.
> 
> 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 [2] for CAP_SYS_ADMIN: "Note: this capability
> is overloaded; see Notes to kernel developers, below." For backward
> compatibility reasons access to system performance monitoring and
> observability subsystems of the kernel remains open for CAP_SYS_ADMIN
> privileged processes but CAP_SYS_ADMIN capability usage for secure
> system performance monitoring and observability operations is
> discouraged with respect to the designed CAP_PERFMON capability.
> 
> Possible alternative solution to this system security hardening,
> capabilities balancing task of making performance monitoring and
> observability operations more secure and accessible could be to use
> the existing CAP_SYS_PTRACE capability to govern system performance
> monitoring and observability subsystems. However CAP_SYS_PTRACE
> capability still provides users with more credentials than are
> required for secure performance monitoring and observability
> operations and this excess is avoided by the designed CAP_PERFMON.
> 
> Although software running under CAP_PERFMON can not ensure avoidance of
> related hardware issues, the software can still mitigate those issues
> following the official hardware issues mitigation procedure [3]. The
> bugs in the software itself can be fixed following the standard kernel
> development process [4] to maintain and harden security of system
> performance monitoring and observability operations. Finally, the patch
> set is shaped in the way that simplifies backtracking procedure of
> possible induced issues [5] as much as possible.
> 
> The patch set is for tip perf/core repository:
> git://git.kernel.org/pub/scm/linux/kernel/git/tip/tip perf/core
> sha1: fdb64822443ec9fb8c3a74b598a74790ae8d2e22
> 
> ---
> Changes in v7:
> - updated and extended kernel.rst and perf-security.rst documentation 
>   files with the information about CAP_PERFMON capability and its use cases
> - documented the case of double audit logging of CAP_PERFMON and CAP_SYS_ADMIN
>   capabilities on a SELinux enabled system
> Changes in v6:
> - avoided noaudit checks in perfmon_capable() to explicitly advertise
>   CAP_PERFMON usage thru audit logs to secure system performance
>   monitoring and observability
> Changes in v5:
> - renamed CAP_SYS_PERFMON to CAP_PERFMON
> - extended perfmon_capable() with noaudit checks
> Changes in v4:
> - converted perfmon_capable() into an inline function
> - made perf_events kprobes, uprobes, hw breakpoints and namespaces data
>   available to CAP_SYS_PERFMON privileged processes
> - applied perfmon_capable() to drivers/perf and drivers/oprofile
> - extended __cmd_ftrace() with support of CAP_SYS_PERFMON
> Changes in v3:
> - implemented perfmon_capable() macros aggregating required capabilities
>   checks
> Changes in v2:
> - made perf_events trace points available to CAP_SYS_PERFMON privileged
>   processes
> - made perf_event_paranoid_check() treat CAP_SYS_PERFMON equally to
>   CAP_SYS_ADMIN
> - applied CAP_SYS_PERFMON to i915_perf, bpf_trace, powerpc and parisc
>   system performance monitoring and observability related subsystems
> 
> ---
> Alexey Budankov (12):
>   capabilities: introduce CAP_PERFMON to kernel and user space
>   perf/core: open access to the core for CAP_PERFMON privileged process
>   perf/core: open access to probes for CAP_PERFMON privileged process
>   perf tool: extend Perf tool with CAP_PERFMON capability support
>   drm/i915/perf: open access for CAP_PERFMON privileged process
>   trace/bpf_trace: open access for CAP_PERFMON privileged process
>   powerpc/perf: open access for CAP_PERFMON privileged process
>   parisc/perf: open access for CAP_PERFMON privileged process
>   drivers/perf: open access for CAP_PERFMON privileged process
>   drivers/oprofile: open access for CAP_PERFMON privileged process
>   doc/admin-guide: update perf-security.rst with CAP_PERFMON information
>   doc/admin-guide: update kernel.rst with CAP_PERFMON information
> 
>  Documentation/admin-guide/perf-security.rst | 65 +++++++++++++--------
>  Documentation/admin-guide/sysctl/kernel.rst | 16 +++--
>  arch/parisc/kernel/perf.c                   |  2 +-
>  arch/powerpc/perf/imc-pmu.c                 |  4 +-
>  drivers/gpu/drm/i915/i915_perf.c            | 13 ++---
>  drivers/oprofile/event_buffer.c             |  2 +-
>  drivers/perf/arm_spe_pmu.c                  |  4 +-
>  include/linux/capability.h                  |  4 ++
>  include/linux/perf_event.h                  |  6 +-
>  include/uapi/linux/capability.h             |  8 ++-
>  kernel/events/core.c                        |  6 +-
>  kernel/trace/bpf_trace.c                    |  2 +-
>  security/selinux/include/classmap.h         |  4 +-
>  tools/perf/builtin-ftrace.c                 |  5 +-
>  tools/perf/design.txt                       |  3 +-
>  tools/perf/util/cap.h                       |  4 ++
>  tools/perf/util/evsel.c                     | 10 ++--
>  tools/perf/util/util.c                      |  1 +
>  18 files changed, 98 insertions(+), 61 deletions(-)
> 
> ---
> Validation (Intel Skylake, 8 cores, Fedora 29, 5.5.0-rc3+, x86_64):
> 
> libcap library [6], [7], [8] and Perf tool can be used to apply
> CAP_PERFMON capability for secure system performance monitoring and
> observability beyond the scope permitted by the system wide
> perf_event_paranoid kernel setting [9] and below are the steps for
> evaluation:
> 
>   - patch, build and boot the kernel
>   - patch, build Perf tool e.g. to /home/user/perf
>   ...
>   # git clone git://git.kernel.org/pub/scm/libs/libcap/libcap.git libcap
>   # pushd libcap
>   # patch libcap/include/uapi/linux/capabilities.h with [PATCH 1]
>   # make
>   # pushd progs
>   # ./setcap "cap_perfmon,cap_sys_ptrace,cap_syslog=ep" /home/user/perf
>   # ./setcap -v "cap_perfmon,cap_sys_ptrace,cap_syslog=ep" /home/user/perf
>   /home/user/perf: OK
>   # ./getcap /home/user/perf
>   /home/user/perf = cap_sys_ptrace,cap_syslog,cap_perfmon+ep
>   # echo 2 > /proc/sys/kernel/perf_event_paranoid
>   # cat /proc/sys/kernel/perf_event_paranoid 
>   2
>   ...
>   $ /home/user/perf top
>     ... works as expected ...
>   $ cat /proc/`pidof perf`/status
>   Name:	perf
>   Umask:	0002
>   State:	S (sleeping)
>   Tgid:	2958
>   Ngid:	0
>   Pid:	2958
>   PPid:	9847
>   TracerPid:	0
>   Uid:	500	500	500	500
>   Gid:	500	500	500	500
>   FDSize:	256
>   ...
>   CapInh:	0000000000000000
>   CapPrm:	0000004400080000
>   CapEff:	0000004400080000 => 01000100 00000000 00001000 00000000 00000000
>                                      cap_perfmon,cap_sys_ptrace,cap_syslog
>   CapBnd:	0000007fffffffff
>   CapAmb:	0000000000000000
>   NoNewPrivs:	0
>   Seccomp:	0
>   Speculation_Store_Bypass:	thread vulnerable
>   Cpus_allowed:	ff
>   Cpus_allowed_list:	0-7
>   ...
> 
> Usage of cap_perfmon effectively avoids unused credentials excess:
> 
> - with cap_sys_admin:
>   CapEff:	0000007fffffffff => 01111111 11111111 11111111 11111111 11111111
> 
> - with cap_perfmon:
>   CapEff:	0000004400080000 => 01000100 00000000 00001000 00000000 00000000
>                                     38   34               19
>                                perfmon   syslog           sys_ptrace
> 
> ---
> [1] https://www.kernel.org/doc/html/latest/admin-guide/perf-security.html
> [2] http://man7.org/linux/man-pages/man7/capabilities.7.html
> [3] https://www.kernel.org/doc/html/latest/process/embargoed-hardware-issues.html
> [4] https://www.kernel.org/doc/html/latest/admin-guide/security-bugs.html
> [5] https://www.kernel.org/doc/html/latest/process/management-style.html#decisions
> [6] http://man7.org/linux/man-pages/man8/setcap.8.html
> [7] https://git.kernel.org/pub/scm/libs/libcap/libcap.git
> [8] https://sites.google.com/site/fullycapable/, posix_1003.1e-990310.pdf
> [9] http://man7.org/linux/man-pages/man2/perf_event_open.2.html
>