perf_event_open is not restricted to admin by default

[Thadeu Lima de Souza Cascardo]

[Impact]
perf_event_open is not restricted by default, which means unprivileged users may have access to information they should not have.

[Test case]
Run as an unprivileged user:
perf stat true
and check that it fails.

[Potential regression]
Users who expect to be able to use perf will not be able to do it. The fix might also cause the build to fail, in case it doesn't match enforced config options.

[Launchpad Janitor (janitor)]

This bug was fixed in the package linux-raspi2 - 4.15.0-1078.83

---------------
linux-raspi2 (4.15.0-1078.83) bionic; urgency=medium

  * bionic/linux-raspi2: 4.15.0-1078.83 -proposed tracker (LP: #1911270)

  * perf_event_open is not restricted to admin by default (LP: #1905786)
    - [Config]: set CONFIG_SECURITY_PERF_EVENTS_RESTRICT

  [ Ubuntu: 4.15.0-133.137 ]

  * bionic/linux: 4.15.0-133.137 -proposed tracker (LP: #1911295)
  * [drm:qxl_enc_commit [qxl]] *ERROR* head number too large or missing monitors
    config: (LP: #1908219)
    - qxl: remove qxl_io_log()
    - qxl: move qxl_send_monitors_config()
    - qxl: hook monitors_config updates into crtc, not encoder.
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    - Input: i8042 - add ByteSpeed touchpad to noloop table
  * vmx_nm_test in ubuntu_kvm_unit_tests interrupted on X-oracle-4.15 /
    B-oracle-4.15 / X-KVM / B-KVM (LP: #1872401)
    - KVM: nVMX: Always reflect #NM VM-exits to L1
  * stack trace in kernel (LP: #1903596)
    - net: napi: remove useless stack trace
  * CVE-2020-27777
    - [Config]: Set CONFIG_PPC_RTAS_FILTER
  * Bionic update: upstream stable patchset 2020-12-04 (LP: #1906875)
    - regulator: defer probe when trying to get voltage from unresolved supply
    - ring-buffer: Fix recursion protection transitions between interrupt context
    - time: Prevent undefined behaviour in timespec64_to_ns()
    - nbd: don't update block size after device is started
    - btrfs: sysfs: init devices outside of the chunk_mutex
    - btrfs: reschedule when cloning lots of extents
    - genirq: Let GENERIC_IRQ_IPI select IRQ_DOMAIN_HIERARCHY
    - hv_balloon: disable warning when floor reached
    - net: xfrm: fix a race condition during allocing spi
    - perf tools: Add missing swap for ino_generation
    - ALSA: hda: prevent undefined shift in snd_hdac_ext_bus_get_link()
    - can: rx-offload: don't call kfree_skb() from IRQ context
    - can: dev: can_get_echo_skb(): prevent call to kfree_skb() in hard IRQ
      context
    - can: dev: __can_get_echo_skb(): fix real payload length return value for RTR
      frames
    - can: can_create_echo_skb(): fix echo skb generation: always use skb_clone()
    - can: peak_usb: add range checking in decode operations
    - can: peak_usb: peak_usb_get_ts_time(): fix timestamp wrapping
    - can: peak_canfd: pucan_handle_can_rx(): fix echo management when loopback is
      on
    - xfs: flush new eof page on truncate to avoid post-eof corruption
    - Btrfs: fix missing error return if writeback for extent buffer never started
    - ath9k_htc: Use appropriate rs_datalen type
    - usb: gadget: goku_udc: fix potential crashes in probe
    - gfs2: Free rd_bits later in gfs2_clear_rgrpd to fix use-after-free
    - gfs2: Add missing truncate_inode_pages_final for sd_aspace
    - gfs2: check for live vs. read-only file system in gfs2_fitrim
    - scsi: hpsa: Fix memory leak in hpsa_init_one()
    - drm/amdgpu: perform srbm soft reset always on SDMA resume
    - mac80211: fix use of skb payload instead of header
    - cfg80211: regulatory: Fix inconsistent format argument
    - scsi: scsi_dh_alua: Avoid crash during alua_bus...