From 3089c1df10e2931b1d72d2ffa7d86431084c86b3 Mon Sep 17 00:00:00 2001 From: =?utf8?q?Nicolai=20H=C3=A4hnle?= Date: Sat, 18 Feb 2017 22:59:56 +0100 Subject: [PATCH] drm/ttm: fix use-after-free races in vm fault handling MIME-Version: 1.0 Content-Type: text/plain; charset=utf8 Content-Transfer-Encoding: 8bit The vm fault handler relies on the fact that the VMA owns a reference to the BO. However, once mmap_sem is released, other tasks are free to destroy the VMA, which can lead to the BO being freed. Fix two code paths where that can happen, both related to vm fault retries. Found via a lock debugging warning which flagged &bo->wu_mutex as locked while being destroyed. Fixes: cbe12e74ee4e ("drm/ttm: Allow vm fault retries") Signed-off-by: Nicolai Hähnle Reviewed-by: Christian König Signed-off-by: Alex Deucher --- drivers/gpu/drm/ttm/ttm_bo_vm.c | 12 ++++++++++++ 1 file changed, 12 insertions(+) diff --git a/drivers/gpu/drm/ttm/ttm_bo_vm.c b/drivers/gpu/drm/ttm/ttm_bo_vm.c index 68ef993ab431..88169141bef5 100644 --- a/drivers/gpu/drm/ttm/ttm_bo_vm.c +++ b/drivers/gpu/drm/ttm/ttm_bo_vm.c @@ -66,8 +66,11 @@ static int ttm_bo_vm_fault_idle(struct ttm_buffer_object *bo, if (vmf->flags & FAULT_FLAG_RETRY_NOWAIT) goto out_unlock; + ttm_bo_reference(bo); up_read(&vma->vm_mm->mmap_sem); (void) dma_fence_wait(bo->moving, true); + ttm_bo_unreserve(bo); + ttm_bo_unref(&bo); goto out_unlock; } @@ -120,8 +123,10 @@ static int ttm_bo_vm_fault(struct vm_area_struct *vma, struct vm_fault *vmf) if (vmf->flags & FAULT_FLAG_ALLOW_RETRY) { if (!(vmf->flags & FAULT_FLAG_RETRY_NOWAIT)) { + ttm_bo_reference(bo); up_read(&vma->vm_mm->mmap_sem); (void) ttm_bo_wait_unreserved(bo); + ttm_bo_unref(&bo); } return VM_FAULT_RETRY; @@ -166,6 +171,13 @@ static int ttm_bo_vm_fault(struct vm_area_struct *vma, struct vm_fault *vmf) ret = ttm_bo_vm_fault_idle(bo, vma, vmf); if (unlikely(ret != 0)) { retval = ret; + + if (retval == VM_FAULT_RETRY && + !(vmf->flags & FAULT_FLAG_RETRY_NOWAIT)) { + /* The BO has already been unreserved. */ + return retval; + } + goto out_unlock; } -- 2.20.1