Description
In the Linux kernel, the following vulnerability has been resolved:drm/i915/gt: Fix timeline left held on VMA alloc errorThe following error has been reported sporadically by CI when a testunbinds the i915 driver on a ring submission platform:<4> [239.330153] ------------[ cut here ]------------<4> [239.330166] i915 0000:00:02.0: [drm] drm_WARN_ON(dev_priv->mm.shrink_count)<4> [239.330196] WARNING: CPU: 1 PID: 18570 at drivers/gpu/drm/i915/i915_gem.c:1309 i915_gem_cleanup_early+0x13e/0x150 [i915]...<4> [239.330640] RIP: 0010:i915_gem_cleanup_early+0x13e/0x150 [i915]...<4> [239.330942] Call Trace:<4> [239.330944] <4> [239.330949] i915_driver_late_release+0x2b/0xa0 [i915]<4> [239.331202] i915_driver_release+0x86/0xa0 [i915]<4> [239.331482] devm_drm_dev_init_release+0x61/0x90<4> [239.331494] devm_action_release+0x15/0x30<4> [239.331504] release_nodes+0x3d/0x120<4> [239.331517] devres_release_all+0x96/0xd0<4> [239.331533] device_unbind_cleanup+0x12/0x80<4> [239.331543] device_release_driver_internal+0x23a/0x280<4> [239.331550] ? bus_find_device+0xa5/0xe0<4> [239.331563] device_driver_detach+0x14/0x20...<4> [357.719679] ---[ end trace 0000000000000000 ]---If the test also unloads the i915 module then that's followed with:<3> [357.787478] =============================================================================<3> [357.788006] BUG i915_vma (Tainted: G U W N ): Objects remaining on __kmem_cache_shutdown()<3> [357.788031] -----------------------------------------------------------------------------<3> [357.788204] Object 0xffff888109e7f480 @offset=29824<3> [357.788670] Allocated in i915_vma_instance+0xee/0xc10 [i915] age=292729 cpu=4 pid=2244<4> [357.788994] i915_vma_instance+0xee/0xc10 [i915]<4> [357.789290] init_status_page+0x7b/0x420 [i915]<4> [357.789532] intel_engines_init+0x1d8/0x980 [i915]<4> [357.789772] intel_gt_init+0x175/0x450 [i915]<4> [357.790014] i915_gem_init+0x113/0x340 [i915]<4> [357.790281] i915_driver_probe+0x847/0xed0 [i915]<4> [357.790504] i915_pci_probe+0xe6/0x220 [i915]...Closer analysis of CI results history has revealed a dependency of theerror on a few IGT tests, namely:- igt@api_intel_allocator@fork-simple-stress-signal,- igt@api_intel_allocator@two-level-inception-interruptible,- igt@gem_linear_blits@interruptible,- igt@prime_mmap_coherency@ioctl-errors,which invisibly trigger the issue, then exhibited with first driver unbindattempt.All of the above tests perform actions which are actively interrupted withsignals. Further debugging has allowed to narrow that scope down toDRM_IOCTL_I915_GEM_EXECBUFFER2, and ring_context_alloc(), specific to ringsubmission, in particular.If successful then that function, or its execlists or GuC submissionequivalent, is supposed to be called only once per GEM context engine,followed by raise of a flag that prevents the function from being calledagain. The function is expected to unwind its internal errors itself, soit may be safely called once more after it returns an error.In case of ring submission, the function first gets a reference to theengine's legacy timeline and then allocates a VMA. If the VMA allocationfails, e.g. when i915_vma_instance() called from inside is interruptedwith a signal, then ring_context_alloc() fails, leaving the timeline heldreferenced. On next I915_GEM_EXECBUFFER2 IOCTL, another reference to thetimeline is got, and only that last one is put on successful completion.As a consequence, the legacy timeline, with its underlying engine statuspage's VMA object, is still held and not released on driver unbind.Get the legacy timeline only after successful allocation of the contextengine's VMA.v2: Add a note on other submission methods (Krzysztof Karas): Both execlists and GuC submission use lrc_alloc() which seems free from a similar issue.(cherry picked from commit cc43422b3cc79eacff4c5a8ba0d224688ca9dd4f)
POC
Reference
No PoCs from references.
Github
- https://github.com/w4zu/Debian_security
