CVE-2021-46976: drm/i915: Fix crash in auto_retire
In the Linux kernel, the following vulnerability has been resolved:

drm/i915: Fix crash in auto_retire

The retire logic uses the 2 lower bits of the pointer to the retire
function to store flags. However, the auto_retire function is not
guaranteed to be aligned to a multiple of 4, which causes crashes as
we jump to the wrong address, for example like this:

2021-04-24T18:03:53.804300Z WARNING kernel: [  516.876901] invalid opcode: 0000 [#1] PREEMPT SMP NOPTI
2021-04-24T18:03:53.804310Z WARNING kernel: [  516.876906] CPU: 7 PID: 146 Comm: kworker/u16:6 Tainted: G     U            5.4.105-13595-g3cd84167b2df #1
2021-04-24T18:03:53.804311Z WARNING kernel: [  516.876907] Hardware name: Google Volteer2/Volteer2, BIOS Google_Volteer2.13672.76.0 02/22/2021
2021-04-24T18:03:53.804312Z WARNING kernel: [  516.876911] Workqueue: events_unbound active_work
2021-04-24T18:03:53.804313Z WARNING kernel: [  516.876914] RIP: 0010:auto_retire+0x1/0x20
2021-04-24T18:03:53.804314Z WARNING kernel: [  516.876916] Code: e8 01 f2 ff ff eb 02 31 db 48 89 d8 5b 5d c3 0f 1f 44 00 00 55 48 89 e5 f0 ff 87 c8 00 00 00 0f 88 ab 47 4a 00 31 c0 5d c3 0f <1f> 44 00 00 55 48 89 e5 f0 ff 8f c8 00 00 00 0f 88 9a 47 4a 00 74
2021-04-24T18:03:53.804319Z WARNING kernel: [  516.876918] RSP: 0018:ffff9b4d809fbe38 EFLAGS: 00010286
2021-04-24T18:03:53.804320Z WARNING kernel: [  516.876919] RAX: 0000000000000007 RBX: ffff927915079600 RCX: 0000000000000007
2021-04-24T18:03:53.804320Z WARNING kernel: [  516.876921] RDX: ffff9b4d809fbe40 RSI: 0000000000000286 RDI: ffff927915079600
2021-04-24T18:03:53.804321Z WARNING kernel: [  516.876922] RBP: ffff9b4d809fbe68 R08: 8080808080808080 R09: fefefefefefefeff
2021-04-24T18:03:53.804321Z WARNING kernel: [  516.876924] R10: 0000000000000010 R11: ffffffff92e44bd8 R12: ffff9279150796a0
2021-04-24T18:03:53.804322Z WARNING kernel: [  516.876925] R13: ffff92791c368180 R14: ffff927915079640 R15: 000000001c867605
2021-04-24T18:03:53.804323Z WARNING kernel: [  516.876926] FS:  0000000000000000(0000) GS:ffff92791ffc0000(0000) knlGS:0000000000000000
2021-04-24T18:03:53.804323Z WARNING kernel: [  516.876928] CS:  0010 DS: 0000 ES: 0000 CR0: 0000000080050033
2021-04-24T18:03:53.804324Z WARNING kernel: [  516.876929] CR2: 0000239514955000 CR3: 00000007f82da001 CR4: 0000000000760ee0
2021-04-24T18:03:53.804325Z WARNING kernel: [  516.876930] PKRU: 55555554
2021-04-24T18:03:53.804325Z WARNING kernel: [  516.876931] Call Trace:
2021-04-24T18:03:53.804326Z WARNING kernel: [  516.876935]  __active_retire+0x77/0xcf
2021-04-24T18:03:53.804326Z WARNING kernel: [  516.876939]  process_one_work+0x1da/0x394
2021-04-24T18:03:53.804327Z WARNING kernel: [  516.876941]  worker_thread+0x216/0x375
2021-04-24T18:03:53.804327Z WARNING kernel: [  516.876944]  kthread+0x147/0x156
2021-04-24T18:03:53.804335Z WARNING kernel: [  516.876946]  ? pr_cont_work+0x58/0x58
2021-04-24T18:03:53.804335Z WARNING kernel: [  516.876948]  ? kthread_blkcg+0x2e/0x2e
2021-04-24T18:03:53.804336Z WARNING kernel: [  516.876950]  ret_from_fork+0x1f/0x40
2021-04-24T18:03:53.804336Z WARNING kernel: [  516.876952] Modules linked in: cdc_mbim cdc_ncm cdc_wdm xt_cgroup rfcomm cmac algif_hash algif_skcipher af_alg xt_MASQUERADE uinput snd_soc_rt5682_sdw snd_soc_rt5682 snd_soc_max98373_sdw snd_soc_max98373 snd_soc_rl6231 regmap_sdw snd_soc_sof_sdw snd_soc_hdac_hdmi snd_soc_dmic snd_hda_codec_hdmi snd_sof_pci snd_sof_intel_hda_common intel_ipu6_psys snd_sof_xtensa_dsp soundwire_intel soundwire_generic_allocation soundwire_cadence snd_sof_intel_hda snd_sof snd_soc_hdac_hda snd_soc_acpi_intel_match snd_soc_acpi snd_hda_ext_core soundwire_bus snd_hda_intel snd_intel_dspcfg snd_hda_codec snd_hwdep snd_hda_core intel_ipu6_isys videobuf2_dma_contig videobuf2_v4l2 videobuf2_common videobuf2_memops mei_hdcp intel_ipu6 ov2740 ov8856 at24 sx9310 dw9768 v4l2_fwnode cros_ec_typec intel_pmc_mux roles acpi_als typec fuse iio_trig_sysfs cros_ec_light_prox cros_ec_lid_angle cros_ec_sensors cros
---truncated---
CVSS v3.1: 5.5