Re: [Intel-gfx] [PATCH v7 00/12] Introduce CAP_PERFMON to secure system performance monitoring and observability

[James Morris <jmorris@namei.org>]

On Sun, 1 Mar 2020, Serge Hallyn wrote:

> Thanks, this looks good to me, in keeping with the CAP_SYSLOG break.
> 
> Acked-by: Serge E. Hallyn <serge@hallyn.com>
> 
> for the set.
> 
> James/Ingo/Peter, if noone has remaining objections, whose branch
> should these go in through?
> 
> thanks,

I was assuming via the perf tree, but I am happy to take them.


> -serge
> 
> On Tue, Feb 25, 2020 at 12:55:54PM +0300, Alexey Budankov wrote:
> > 
> > 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
> > > 
> > _______________________________________________
> > Intel-gfx mailing list
> > Intel-gfx@lists.freedesktop.org
> > https://lists.freedesktop.org/mailman/listinfo/intel-gfx
> 

-- 
James Morris
<jmorris@namei.org>