Subject: CVE-2021-46976: drm/i915: Fix crash in auto_retire

From: Greg Kroah-Hartman <[email-masked]>

Description
===========

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_ec_sensors_core industrialio_triggered_buffer cros_ec_sensors_ring kfifo_buf industrialio cros_ec_sensorhub
2021-04-24T18:03:53.804337Z WARNING kernel: [  516.876972]  cdc_ether usbnet iwlmvm lzo_rle lzo_compress iwl7000_mac80211 iwlwifi zram cfg80211 r8152 mii btusb btrtl btintel btbcm bluetooth ecdh_generic ecc joydev
2021-04-24T18:03:53.804337Z EMERG kernel: [  516.879169] gsmi: Log Shutdown Reason 0x03

This change fixes this by aligning the function.

(cherry picked from commit ca419f407b43cc89942ebc297c7a63d94abbcae4)

The Linux kernel CVE team has assigned CVE-2021-46976 to this issue.

Affected and fixed versions
===========================

	Issue introduced in 5.8 with commit 229007e02d69 and fixed in 5.10.38 with commit 805c990a9c54
	Issue introduced in 5.8 with commit 229007e02d69 and fixed in 5.11.22 with commit 608441de3976
	Issue introduced in 5.8 with commit 229007e02d69 and fixed in 5.12.5 with commit f7520970d535
	Issue introduced in 5.8 with commit 229007e02d69 and fixed in 5.13 with commit 402be8a10119

Please see https://www.kernel.org for a full list of currently supported
kernel versions by the kernel community.

Unaffected versions might change over time as fixes are backported to
older supported kernel versions.  The official CVE entry at
	https://cve.org/CVERecord/?id=CVE-2021-46976
will be updated if fixes are backported, please check that for the most
up to date information about this issue.

Affected files
==============

The file(s) affected by this issue are:
	drivers/gpu/drm/i915/i915_active.c

Mitigation
==========

The Linux kernel CVE team recommends that you update to the latest
stable kernel version for this, and many other bugfixes.  Individual
changes are never tested alone, but rather are part of a larger kernel
release.  Cherry-picking individual commits is not recommended or
supported by the Linux kernel community at all.  If however, updating to
the latest release is impossible, the individual changes to resolve this
issue can be found at these commits:
	https://git.kernel.org/stable/c/805c990a9c54b9451d3daff640b850909c31ab9d
	https://git.kernel.org/stable/c/608441de3976c526b02af4d7063093c8adf351e3
	https://git.kernel.org/stable/c/f7520970d5353cb1fa4d9089a1b23669c5da97fe
	https://git.kernel.org/stable/c/402be8a101190969fc7ff122d07e262df86e132b