Allow BPF tracing under lockdown

This bug is awaiting verification that the kernel in -proposed solves the problem. Please test the kernel and update this bug with the results. If the problem is solved, change the tag 'verification-needed-eoan' to 'verification-done-eoan'. If the problem still exists, change the tag 'verification-needed-eoan' to 'verification-failed-eoan'.

If verification is not done by 5 working days from today, this fix will be dropped from the source code, and this bug will be closed.

See https://wiki.ubuntu.com/Testing/EnableProposed for documentation how to enable and use -proposed. Thank you!

This really should be turned into a test case. @cascardo, to your knowledge, does this test case exist in the current bpf test suite?

ubuntu@eoan:~$ uname -r
5.3.0-46-generic
ubuntu@eoan:~$ grep -i lockdown /proc/cmdline
BOOT_IMAGE=/boot/vmlinuz-5.3.0-46-generic root=PARTUUID=486ca49b-7073-4f42-84a9-c3724b219786 ro console=tty1 console=ttyS0 lockdown
ubuntu@eoan:~$ dmesg | grep -i lockdown
[ 0.000000] Command line: BOOT_IMAGE=/boot/vmlinuz-5.3.0-46-generic root=PARTUUID=486ca49b-7073-4f42-84a9-c3724b219786 ro console=tty1 console=ttyS0 lockdown
[ 0.000000] Kernel is locked down from command line; see man kernel_lockdown.7
[ 0.019403] Kernel command line: BOOT_IMAGE=/boot/vmlinuz-5.3.0-46-generic root=PARTUUID=486ca49b-7073-4f42-84a9-c3724b219786 ro console=tty1 console=ttyS0 lockdown
[ 1.389113] Lockdown: swapper/0: Hibernation is restricted; see man kernel_lockdown.7
ubuntu@eoan:~$ sudo bpftrace -e 'tracepoint:syscalls:sys_enter_openat { printf("filename: [%s]; flags: [%d]\n", str(args->filename), args->flags); }'
Attaching 1 probe...
filename: [/proc/interrupts]; flags: [0]
filename: [/proc/stat]; flags: [0]
^C

ubuntu@eoan:~$ sudo bpftrace -e 'kprobe:do_nanosleep { printf("PID %d sleeping\n", pid); }'
Attaching 1 probe...
PID 509 sleeping
PID 509 sleeping
^C

ubuntu@eoan:~$

This bug was fixed in the package linux - 5.3.0-46.38

---------------
linux (5.3.0-46.38) eoan; urgency=medium

  * eoan/linux: 5.3.0-43.36 -proposed tracker (LP: #1867301)

  * Fix AMD Stoney Ridge screen flickering under 4K resolution (LP: #1864005)
    - iommu/amd: Disable IOMMU on Stoney Ridge systems

  * Allow BPF tracing under lockdown (LP: #1868626)
    - Revert "UBUNTU: SAUCE: (efi-lockdown) Lock down kprobes"
    - Revert "bpf: Restrict bpf when kernel lockdown is in confidentiality mode"

  * Missing wireless network interface after kernel 5.3.0-43 upgrade with eoan
    (LP: #1868442)
    - iwlwifi: mvm: Do not require PHY_SKU NVM section for 3168 devices

  * Packaging resync (LP: #1786013)
    - [Packaging] resync getabis
    - [Packaging] update helper scripts

  * iSCSI-target: Deleting a LUN hangs in the kernel (LP: #1862682)
    - scsi: Revert "target/core: Inline transport_lun_remove_cmd()"

  * Stop using get_scalar_status command in Dell AIO uart backlight driver
    (LP: #1865402)
    - SAUCE: platform/x86: dell-uart-backlight: add get_display_mode command

  * Eoan update: upstream stable patchset 2020-03-11 (LP: #1867051)
    - Revert "drm/sun4i: dsi: Change the start delay calculation"
    - ovl: fix lseek overflow on 32bit
    - kernel/module: Fix memleak in module_add_modinfo_attrs()
    - media: iguanair: fix endpoint sanity check
    - ocfs2: fix oops when writing cloned file
    - x86/cpu: Update cached HLE state on write to TSX_CTRL_CPUID_CLEAR
    - udf: Allow writing to 'Rewritable' partitions
    - printk: fix exclusive_console replaying
    - iwlwifi: mvm: fix NVM check for 3168 devices
    - sparc32: fix struct ipc64_perm type definition
    - cls_rsvp: fix rsvp_policy
    - gtp: use __GFP_NOWARN to avoid memalloc warning
    - l2tp: Allow duplicate session creation with UDP
    - net: hsr: fix possible NULL deref in hsr_handle_frame()
    - net_sched: fix an OOB access in cls_tcindex
    - net: stmmac: Delete txtimer in suspend()
    - bnxt_en: Fix TC queue mapping.
    - tcp: clear tp->total_retrans in tcp_disconnect()
    - tcp: clear tp->delivered in tcp_disconnect()
    - tcp: clear tp->data_segs{in|out} in tcp_disconnect()
    - tcp: clear tp->segs_{in|out} in tcp_disconnect()
    - rxrpc: Fix use-after-free in rxrpc_put_local()
    - rxrpc: Fix insufficient receive notification generation
    - rxrpc: Fix missing active use pinning of rxrpc_local object
    - rxrpc: Fix NULL pointer deref due to call->conn being cleared on disconnect
    - media: uvcvideo: Avoid cyclic entity chains due to malformed USB descriptors
    - mfd: dln2: More sanity checking for endpoints
    - ipc/msg.c: consolidate all xxxctl_down() functions
    - tracing: Fix sched switch start/stop refcount racy updates
    - rcu: Avoid data-race in rcu_gp_fqs_check_wake()
    - brcmfmac: Fix memory leak in brcmf_usbdev_qinit
    - usb: typec: tcpci: mask event interrupts when remove driver
    - usb: gadget: legacy: set max_speed to super-speed
    - usb: gadget: f_ncm: Use atomic_t to track in-flight request
    - usb: gadget: f_ecm: Use atomic_t to track in-flight request
    - ALSA: usb-audio: Fix endianess in descriptor validatio...