drm/radeon: fix invalid memory access in radeon_atrm_get_bios()

commit a3f83ab1a717c0e6c2f59a4cfdaa10707cc35c55 upstream.

At a boot time I observed following bug:

 BUG: unable to handle kernel paging request at ffff8800a4244000
 IP: [<ffffffff81275b5b>] memcpy+0xb/0x120
 PGD 1816063 PUD 1fe7d067 PMD 1ff9f067 PTE 80000000a4244160
 Oops: 0000 [#1] SMP DEBUG_PAGEALLOC
 CPU 0
 Modules linked in: btusb bluetooth brcmsmac brcmutil crc8 cordic b43 radeon(+)
  mac80211 cfg80211 ttm ohci_hcd drm_kms_helper rfkill drm ssb agpgart mmc_core
  sp5100_tco video battery ac thermal processor rtc_cmos thermal_sys snd_hda_codec_hdmi
  joydev snd_hda_codec_conexant button bcma pcmcia snd_hda_intel snd_hda_codec
  snd_hwdep snd_pcm shpchp pcmcia_core k8temp snd_timer atl1c snd psmouse hwmon
  i2c_piix4 i2c_algo_bit soundcore evdev i2c_core ehci_hcd sg serio_raw snd_page_alloc
  loop btrfs

 Pid: 1008, comm: modprobe Not tainted 3.3.0-rc1 #21 LENOVO 20046                           /AMD CRB
 RIP: 0010:[<ffffffff81275b5b>]  [<ffffffff81275b5b>] memcpy+0xb/0x120
 RSP: 0018:ffff8800aa72db00  EFLAGS: 00010246
 RAX: ffff8800a4150000 RBX: 0000000000001000 RCX: 0000000000000087
 RDX: 0000000000000000 RSI: ffff8800a4244000 RDI: ffff8800a4150bc8
 RBP: ffff8800aa72db78 R08: 0000000000000010 R09: ffffffff8174bbec
 R10: ffffffff812ee010 R11: 0000000000000001 R12: 0000000000001000
 R13: 0000000000010000 R14: ffff8800a4140000 R15: ffff8800aaba1800
 FS:  00007ff9a3bd4720(0000) GS:ffff8800afa00000(0000) knlGS:0000000000000000
 CS:  0010 DS: 0000 ES: 0000 CR0: 000000008005003b
 CR2: ffff8800a4244000 CR3: 00000000a9c18000 CR4: 00000000000006f0
 DR0: 0000000000000000 DR1: 0000000000000000 DR2: 0000000000000000
 DR3: 0000000000000000 DR6: 00000000ffff0ff0 DR7: 0000000000000400
 Process modprobe (pid: 1008, threadinfo ffff8800aa72c000, task ffff8800aa0e4000)
 Stack:
  ffffffffa04e7c7b 0000000000000001 0000000000010000 ffff8800aa72db28
  ffffffff00000001 0000000000001000 ffffffff8113cbef 0000000000000020
  ffff8800a4243420 ffff880000000002 ffff8800aa72db08 ffff8800a9d42000
 Call Trace:
  [<ffffffffa04e7c7b>] ? radeon_atrm_get_bios_chunk+0x8b/0xd0 [radeon]
  [<ffffffff8113cbef>] ? kmalloc_order_trace+0x3f/0xb0
  [<ffffffffa04a9298>] radeon_get_bios+0x68/0x2f0 [radeon]
  [<ffffffffa04c7a30>] rv770_init+0x40/0x280 [radeon]
  [<ffffffffa047d740>] radeon_device_init+0x560/0x600 [radeon]
  [<ffffffffa047ef4f>] radeon_driver_load_kms+0xaf/0x170 [radeon]
  [<ffffffffa043cdde>] drm_get_pci_dev+0x18e/0x2c0 [drm]
  [<ffffffffa04e7e95>] radeon_pci_probe+0xad/0xb5 [radeon]
  [<ffffffff81296c5f>] local_pci_probe+0x5f/0xd0
  [<ffffffff81297418>] pci_device_probe+0x88/0xb0
  [<ffffffff813417aa>] ? driver_sysfs_add+0x7a/0xb0
  [<ffffffff813418d8>] really_probe+0x68/0x180
  [<ffffffff81341be5>] driver_probe_device+0x45/0x70
  [<ffffffff81341cb3>] __driver_attach+0xa3/0xb0
  [<ffffffff81341c10>] ? driver_probe_device+0x70/0x70
  [<ffffffff813400ce>] bus_for_each_dev+0x5e/0x90
  [<ffffffff8134172e>] driver_attach+0x1e/0x20
  [<ffffffff81341298>] bus_add_driver+0xc8/0x280
  [<ffffffff813422c6>] driver_register+0x76/0x140
  [<ffffffff812976d6>] __pci_register_driver+0x66/0xe0
  [<ffffffffa043d021>] drm_pci_init+0x111/0x120 [drm]
  [<ffffffff8133c67a>] ? vga_switcheroo_register_handler+0x3a/0x60
  [<ffffffffa0229000>] ? 0xffffffffa0228fff
  [<ffffffffa02290ec>] radeon_init+0xec/0xee [radeon]
  [<ffffffff810002f2>] do_one_initcall+0x42/0x180
  [<ffffffff8109d8d2>] sys_init_module+0x92/0x1e0
  [<ffffffff815407a9>] system_call_fastpath+0x16/0x1b
 Code: 58 2a 43 50 88 43 4e 48 83 c4 08 5b c9 c3 66 90 e8 cb fd ff ff eb
  e6 90 90 90 90 90 90 90 90 90 48 89 f8 89 d1 c1 e9 03 83 e2 07 <f3> 48
  a5 89 d1 f3 a4 c3 20 48 83 ea 20 4c 8b 06 4c 8b 4e 08 4c
 RIP  [<ffffffff81275b5b>] memcpy+0xb/0x120
  RSP <ffff8800aa72db00>
 CR2: ffff8800a4244000
 ---[ end trace fcffa1599cf56382 ]---

Call to acpi_evaluate_object() not always returns 4096 bytes chunks,
on my system it can return 2048 bytes chunk, so pass the length of
retrieved chunk to memcpy(), not the length of the recieving buffer.

Signed-off-by: Igor Murzov <e-mail@date.by>
Reviewed-by: Alex Deucher <alexander.deucher@amd.com>
Signed-off-by: Dave Airlie <airlied@redhat.com>
Signed-off-by: Ben Hutchings <ben@decadent.org.uk>