Subject: CVE-2024-41092: drm/i915/gt: Fix potential UAF by revoke of fence registers

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

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

In the Linux kernel, the following vulnerability has been resolved:

drm/i915/gt: Fix potential UAF by revoke of fence registers

CI has been sporadically reporting the following issue triggered by
igt@i915_selftest@live@hangcheck on ADL-P and similar machines:

<6> [414.049203] i915: Running intel_hangcheck_live_selftests/igt_reset_evict_fence
...
<6> [414.068804] i915 0000:00:02.0: [drm] GT0: GUC: submission enabled
<6> [414.068812] i915 0000:00:02.0: [drm] GT0: GUC: SLPC enabled
<3> [414.070354] Unable to pin Y-tiled fence; err:-4
<3> [414.071282] i915_vma_revoke_fence:301 GEM_BUG_ON(!i915_active_is_idle(&fence->active))
...
<4>[  609.603992] ------------[ cut here ]------------
<2>[  609.603995] kernel BUG at drivers/gpu/drm/i915/gt/intel_ggtt_fencing.c:301!
<4>[  609.604003] invalid opcode: 0000 [#1] PREEMPT SMP NOPTI
<4>[  609.604006] CPU: 0 PID: 268 Comm: kworker/u64:3 Tainted: G     U  W          6.9.0-CI_DRM_14785-g1ba62f8cea9c+ #1
<4>[  609.604008] Hardware name: Intel Corporation Alder Lake Client Platform/AlderLake-P DDR4 RVP, BIOS RPLPFWI1.R00.4035.A00.2301200723 01/20/2023
<4>[  609.604010] Workqueue: i915 __i915_gem_free_work [i915]
<4>[  609.604149] RIP: 0010:i915_vma_revoke_fence+0x187/0x1f0 [i915]
...
<4>[  609.604271] Call Trace:
<4>[  609.604273]  <TASK>
...
<4>[  609.604716]  __i915_vma_evict+0x2e9/0x550 [i915]
<4>[  609.604852]  __i915_vma_unbind+0x7c/0x160 [i915]
<4>[  609.604977]  force_unbind+0x24/0xa0 [i915]
<4>[  609.605098]  i915_vma_destroy+0x2f/0xa0 [i915]
<4>[  609.605210]  __i915_gem_object_pages_fini+0x51/0x2f0 [i915]
<4>[  609.605330]  __i915_gem_free_objects.isra.0+0x6a/0xc0 [i915]
<4>[  609.605440]  process_scheduled_works+0x351/0x690
...

In the past, there were similar failures reported by CI from other IGT
tests, observed on other platforms.

Before commit 63baf4f3d587 ("drm/i915/gt: Only wait for GPU activity
before unbinding a GGTT fence"), i915_vma_revoke_fence() was waiting for
idleness of vma->active via fence_update().   That commit introduced
vma->fence->active in order for the fence_update() to be able to wait
selectively on that one instead of vma->active since only idleness of
fence registers was needed.  But then, another commit 0d86ee35097a
("drm/i915/gt: Make fence revocation unequivocal") replaced the call to
fence_update() in i915_vma_revoke_fence() with only fence_write(), and
also added that GEM_BUG_ON(!i915_active_is_idle(&fence->active)) in front.
No justification was provided on why we might then expect idleness of
vma->fence->active without first waiting on it.

The issue can be potentially caused by a race among revocation of fence
registers on one side and sequential execution of signal callbacks invoked
on completion of a request that was using them on the other, still
processed in parallel to revocation of those fence registers.  Fix it by
waiting for idleness of vma->fence->active in i915_vma_revoke_fence().

(cherry picked from commit 24bb052d3dd499c5956abad5f7d8e4fd07da7fb1)

The Linux kernel CVE team has assigned CVE-2024-41092 to this issue.

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

	Issue introduced in 5.8 with commit 0d86ee35097a and fixed in 5.10.221 with commit f771b91f21c4
	Issue introduced in 5.8 with commit 0d86ee35097a and fixed in 5.15.162 with commit 29c0fdf49078
	Issue introduced in 5.8 with commit 0d86ee35097a and fixed in 6.1.97 with commit ca0fabd365a2
	Issue introduced in 5.8 with commit 0d86ee35097a and fixed in 6.6.37 with commit 06dec31a0a51
	Issue introduced in 5.8 with commit 0d86ee35097a and fixed in 6.9.8 with commit 414f4a31f7a8
	Issue introduced in 5.8 with commit 0d86ee35097a and fixed in 6.10 with commit 996c3412a065

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-2024-41092
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/gt/intel_ggtt_fencing.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/f771b91f21c46ad1217328d05e72a2c7e3add535
	https://git.kernel.org/stable/c/29c0fdf49078ab161570d3d1c6e13d66f182717d
	https://git.kernel.org/stable/c/ca0fabd365a27a94a36e68a7a02df8ff3c13dac6
	https://git.kernel.org/stable/c/06dec31a0a5112a91f49085e8a8fa1a82296d5c7
	https://git.kernel.org/stable/c/414f4a31f7a811008fd9a33b06216b060bad18fc
	https://git.kernel.org/stable/c/996c3412a06578e9d779a16b9e79ace18125ab50