linux-kernel - [PATCH 5.11 105/306] drm/shmem-helper: Check for purged buffers in fault handler

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Date:   Mon, 15 Mar 2021 14:52:48 +0100
From:   gregkh@...uxfoundation.org
To:     linux-kernel@...r.kernel.org
Cc:     Greg Kroah-Hartman <gregkh@...uxfoundation.org>,
        stable@...r.kernel.org, Neil Roberts <nroberts@...lia.com>,
        Steven Price <steven.price@....com>,
        Maarten Lankhorst <maarten.lankhorst@...ux.intel.com>
Subject: [PATCH 5.11 105/306] drm/shmem-helper: Check for purged buffers in fault handler

From: Greg Kroah-Hartman <gregkh@...uxfoundation.org>

From: Neil Roberts <nroberts@...lia.com>

commit d611b4a0907cece060699f2fd347c492451cd2aa upstream.

When a buffer is madvised as not needed and then purged, any attempts to
access the buffer from user-space should cause a bus fault. This patch
adds a check for that.

Cc: stable@...r.kernel.org
Fixes: 17acb9f35ed7 ("drm/shmem: Add madvise state and purge helpers")
Signed-off-by: Neil Roberts <nroberts@...lia.com>
Reviewed-by: Steven Price <steven.price@....com>
Signed-off-by: Steven Price <steven.price@....com>
Link: https://patchwork.freedesktop.org/patch/msgid/20210223155125.199577-2-nroberts@igalia.com
Signed-off-by: Maarten Lankhorst <maarten.lankhorst@...ux.intel.com>
Signed-off-by: Greg Kroah-Hartman <gregkh@...uxfoundation.org>
---
 drivers/gpu/drm/drm_gem_shmem_helper.c |   18 ++++++++++++++----
 1 file changed, 14 insertions(+), 4 deletions(-)

--- a/drivers/gpu/drm/drm_gem_shmem_helper.c
+++ b/drivers/gpu/drm/drm_gem_shmem_helper.c
@@ -525,14 +525,24 @@ static vm_fault_t drm_gem_shmem_fault(st
 	struct drm_gem_object *obj = vma->vm_private_data;
 	struct drm_gem_shmem_object *shmem = to_drm_gem_shmem_obj(obj);
 	loff_t num_pages = obj->size >> PAGE_SHIFT;
+	vm_fault_t ret;
 	struct page *page;
 
-	if (vmf->pgoff >= num_pages || WARN_ON_ONCE(!shmem->pages))
-		return VM_FAULT_SIGBUS;
+	mutex_lock(&shmem->pages_lock);
 
-	page = shmem->pages[vmf->pgoff];
+	if (vmf->pgoff >= num_pages ||
+	    WARN_ON_ONCE(!shmem->pages) ||
+	    shmem->madv < 0) {
+		ret = VM_FAULT_SIGBUS;
+	} else {
+		page = shmem->pages[vmf->pgoff];
 
-	return vmf_insert_page(vma, vmf->address, page);
+		ret = vmf_insert_page(vma, vmf->address, page);
+	}
+
+	mutex_unlock(&shmem->pages_lock);
+
+	return ret;
 }
 
 static void drm_gem_shmem_vm_open(struct vm_area_struct *vma)