The tlv passed to iwl_dbg_tlv_alloc_trigger comes from a loaded firmware
file. The memory can be marked as read-only as firmware could be
shared. In anyway, writing to this memory is not expected. So,
iwl_dbg_tlv_alloc_trigger can crash now:

  BUG: unable to handle page fault for address: ffffae2c01bfa794
  PF: supervisor write access in kernel mode
  PF: error_code(0x0003) - permissions violation
  PGD 107d51067 P4D 107d51067 PUD 107d52067 PMD 659ad2067 PTE 8000000662298161
  CPU: 2 PID: 161 Comm: kworker/2:1 Not tainted 5.7.0-3.gad96a07-default #1 openSUSE Tumbleweed (unreleased)
  RIP: 0010:iwl_dbg_tlv_alloc_trigger+0x25/0x60 [iwlwifi]
  Code: eb f2 0f 1f 00 66 66 66 66 90 83 7e 04 33 48 89 f8 44 8b 46 10 48 89 f7 76 40 41 8d 50 ff 83 fa 19 77 23 8b 56 20 85 d2 75 07 <c7> 46 20 ff ff ff ff 4b 8d 14 40 48 c1 e2 04 48 8d b4 10 00 05 00
  RSP: 0018:ffffae2c00417ce8 EFLAGS: 00010246
  RAX: ffff8f0522334018 RBX: ffff8f0522334018 RCX: ffffffffc0fc26c0
  RDX: 0000000000000000 RSI: ffffae2c01bfa774 RDI: ffffae2c01bfa774
  RBP: 0000000000000000 R08: 0000000000000004 R09: 0000000000000001
  R10: 0000000000000034 R11: ffffae2c01bfa77c R12: ffff8f0522334230
  R13: 0000000001000009 R14: ffff8f0523fdbc00 R15: ffff8f051f395800
  FS:  0000000000000000(0000) GS:ffff8f0527c80000(0000) knlGS:0000000000000000
  CS:  0010 DS: 0000 ES: 0000 CR0: 0000000080050033
  CR2: ffffae2c01bfa794 CR3: 0000000389eba000 CR4: 00000000000006e0
  Call Trace:
   iwl_dbg_tlv_alloc+0x79/0x120 [iwlwifi]
   iwl_parse_tlv_firmware.isra.0+0x57d/0x1550 [iwlwifi]
   iwl_req_fw_callback+0x3f8/0x6a0 [iwlwifi]
   request_firmware_work_func+0x47/0x90
   process_one_work+0x1e3/0x3b0
   worker_thread+0x46/0x340
   kthread+0x115/0x140
   ret_from_fork+0x1f/0x40

As can be seen, write bit is not set in the PTE. Read of
trig->occurrences succeeds in iwl_dbg_tlv_alloc_trigger, but
trig->occurrences = cpu_to_le32(-1); fails there, obviously.

This is likely because we (at SUSE) use compressed firmware and that is
marked as RO after decompression (see fw_map_paged_buf).

Fix it by creating a temporary buffer in case we need to change the
memory.
Signed-off-by: Jiri Slaby <jslaby@suse.cz>
Reported-by: Dieter Nützel <Dieter@nuetzel-hh.de>
Tested-by: Dieter Nützel <Dieter@nuetzel-hh.de>
Cc: Johannes Berg <johannes.berg@intel.com>
Cc: Emmanuel Grumbach <emmanuel.grumbach@intel.com>
Cc: Luca Coelho <luciano.coelho@intel.com>
Cc: Intel Linux Wireless <linuxwifi@intel.com>
Cc: Kalle Valo <kvalo@codeaurora.org>
Cc: "David S. Miller" <davem@davemloft.net>
Cc: Jakub Kicinski <kuba@kernel.org>
Cc: linux-wireless@vger.kernel.org
Cc: netdev@vger.kernel.org
Signed-off-by: Kalle Valo <kvalo@codeaurora.org>
Link: https://lore.kernel.org/r/20200612073800.27742-1-jslaby@suse.cz