[PATCH v2 0/4] perf: Use capabilities instead of uid and euid

[Igor Lubashev <ilubashe@akamai.com>]

Series v1: https://lkml.kernel.org/lkml/1562112605-6235-1-git-send-email-ilubashe@akamai.com


Kernel is using capabilities instead of uid and euid to restrict access to
kernel pointers and tracing facilities.  This patch series updates the perf to
better match the security model used by the kernel.

This series enables instructions in Documentation/admin-guide/perf-security.rst
to actually work, even when kernel.perf_event_paranoid=2 and
kernel.kptr_restrict=1.

The series consists of four patches:

  01: perf: Add capability-related utilities
    Add utility functions to check capabilities and perf_event_paranoid checks,
    if libcap-dev[el] is available. (Otherwise, assume no capabilities.)

  02: perf: Use CAP_SYS_ADMIN with perf_event_paranoid checks
    Replace the use of euid==0 with a check for CAP_SYS_ADMIN whenever
    perf_event_paranoid level is verified.

  03: perf: Use CAP_SYSLOG with kptr_restrict checks
    Replace the use of uid and euid with a check for CAP_SYSLOG when
    kptr_restrict is verified (similar to kernel/kallsyms.c and lib/vsprintf.c).
    Consult perf_event_paranoid when kptr_restrict==0 (see kernel/kallsyms.c).

  04: perf: Use CAP_SYS_ADMIN instead of euid==0 with ftrace
    Replace the use of euid==0 with a check for CAP_SYS_ADMIN before mounting
    debugfs for ftrace.

I tested this by following Documentation/admin-guide/perf-security.rst
guidelines and setting sysctls:

   kernel.perf_event_paranoid=2
   kernel.kptr_restrict=1

As an unpriviledged user who is in perf_users group (setup via instructions
above), I executed:
   perf record -a -- sleep 1

Without the patch, perf record did not capture any kernel functions.
With the patch, perf included all kernel funcitons.


Changelog:
v2:  * Added a build feature check for libcap-dev[el] as suggested by Arnaldo


Igor Lubashev (4):
  perf: Add capability-related utilities
  perf: Use CAP_SYS_ADMIN with perf_event_paranoid checks
  perf: Use CAP_SYSLOG with kptr_restrict checks
  perf: Use CAP_SYS_ADMIN instead of euid==0 with ftrace

 tools/build/Makefile.feature         |  2 ++
 tools/build/feature/Makefile         |  4 ++++
 tools/build/feature/test-libcap.c    | 20 ++++++++++++++++++++
 tools/perf/Makefile.config           | 11 +++++++++++
 tools/perf/Makefile.perf             |  2 ++
 tools/perf/arch/arm/util/cs-etm.c    |  3 ++-
 tools/perf/arch/arm64/util/arm-spe.c |  4 ++--
 tools/perf/arch/x86/util/intel-bts.c |  3 ++-
 tools/perf/arch/x86/util/intel-pt.c  |  2 +-
 tools/perf/builtin-ftrace.c          |  4 +++-
 tools/perf/util/Build                |  2 ++
 tools/perf/util/cap.c                | 29 +++++++++++++++++++++++++++++
 tools/perf/util/cap.h                | 24 ++++++++++++++++++++++++
 tools/perf/util/event.h              |  1 +
 tools/perf/util/evsel.c              |  2 +-
 tools/perf/util/python-ext-sources   |  1 +
 tools/perf/util/symbol.c             | 15 +++++++++++----
 tools/perf/util/util.c               |  9 +++++++++
 18 files changed, 127 insertions(+), 11 deletions(-)
 create mode 100644 tools/build/feature/test-libcap.c
 create mode 100644 tools/perf/util/cap.c
 create mode 100644 tools/perf/util/cap.h

-- 
2.7.4