[PATCH v16 15/20] drm/shmem-helper: Add memory shrinker

[Dan Carpenter]

Hi Dmitry,

kernel test robot noticed the following build warnings:

https://git-scm.com/docs/git-format-patch#_base_tree_information]

url:    https://github.com/intel-lab-lkp/linux/commits/Dmitry-Osipenko/drm-shmem-helper-Fix-UAF-in-error-path-when-freeing-SGT-of-imported-GEM/20230904-011037
base:   linus/master
patch link:    https://lore.kernel.org/r/20230903170736.513347-16-dmitry.osipenko%40collabora.com
patch subject: [PATCH v16 15/20] drm/shmem-helper: Add memory shrinker
config: x86_64-randconfig-161-20230907 (https://download.01.org/0day-ci/archive/20230907/202309070814.jyGJOJzY-lkp@intel.com/config)
compiler: gcc-12 (Debian 12.2.0-14) 12.2.0
reproduce: (https://download.01.org/0day-ci/archive/20230907/202309070814.jyGJOJzY-lkp@intel.com/reproduce)

If you fix the issue in a separate patch/commit (i.e. not just a new version of
the same patch/commit), kindly add following tags
| Reported-by: kernel test robot <lkp at intel.com>
| Reported-by: Dan Carpenter <dan.carpenter at linaro.org>
| Closes: https://lore.kernel.org/r/202309070814.jyGJOJzY-lkp@intel.com/

smatch warnings:
drivers/gpu/drm/drm_gem_shmem_helper.c:733 drm_gem_shmem_fault() error: we previously assumed 'shmem->pages' could be null (see line 724)

vim +733 drivers/gpu/drm/drm_gem_shmem_helper.c

2194a63a818db7 Noralf Trønnes  2019-03-12  702  static vm_fault_t drm_gem_shmem_fault(struct vm_fault *vmf)
2194a63a818db7 Noralf Trønnes  2019-03-12  703  {
2194a63a818db7 Noralf Trønnes  2019-03-12  704  	struct vm_area_struct *vma = vmf->vma;
2194a63a818db7 Noralf Trønnes  2019-03-12  705  	struct drm_gem_object *obj = vma->vm_private_data;
2194a63a818db7 Noralf Trønnes  2019-03-12  706  	struct drm_gem_shmem_object *shmem = to_drm_gem_shmem_obj(obj);
2194a63a818db7 Noralf Trønnes  2019-03-12  707  	loff_t num_pages = obj->size >> PAGE_SHIFT;
d611b4a0907cec Neil Roberts    2021-02-23  708  	vm_fault_t ret;
2194a63a818db7 Noralf Trønnes  2019-03-12  709  	struct page *page;
11d5a4745e00e7 Neil Roberts    2021-02-23  710  	pgoff_t page_offset;
2c607edf57db6a Dmitry Osipenko 2023-09-03  711  	bool pages_unpinned;
2c607edf57db6a Dmitry Osipenko 2023-09-03  712  	int err;
11d5a4745e00e7 Neil Roberts    2021-02-23  713  
11d5a4745e00e7 Neil Roberts    2021-02-23  714  	/* We don't use vmf->pgoff since that has the fake offset */
11d5a4745e00e7 Neil Roberts    2021-02-23  715  	page_offset = (vmf->address - vma->vm_start) >> PAGE_SHIFT;
2194a63a818db7 Noralf Trønnes  2019-03-12  716  
21aa27ddc58269 Dmitry Osipenko 2023-05-30  717  	dma_resv_lock(shmem->base.resv, NULL);
2194a63a818db7 Noralf Trønnes  2019-03-12  718  
2c607edf57db6a Dmitry Osipenko 2023-09-03  719  	/* Sanity-check that we have the pages pointer when it should present */
2c607edf57db6a Dmitry Osipenko 2023-09-03  720  	pages_unpinned = (shmem->evicted || shmem->madv < 0 ||
2c607edf57db6a Dmitry Osipenko 2023-09-03  721  			  !refcount_read(&shmem->pages_use_count));
2c607edf57db6a Dmitry Osipenko 2023-09-03  722  	drm_WARN_ON_ONCE(obj->dev, !shmem->pages ^ pages_unpinned);
2c607edf57db6a Dmitry Osipenko 2023-09-03  723  
2c607edf57db6a Dmitry Osipenko 2023-09-03 @724  	if (page_offset >= num_pages || (!shmem->pages && !shmem->evicted)) {
                                                                                          ^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^
Should this be || instead of &&?  (The other thing that people do is
add "!shmem->evicted" for readability even though it doesn't need to be
checked.  So maybe that's the issue, but the checker assumes it needs to
be checked).

d611b4a0907cec Neil Roberts    2021-02-23  725  		ret = VM_FAULT_SIGBUS;
d611b4a0907cec Neil Roberts    2021-02-23  726  	} else {
2c607edf57db6a Dmitry Osipenko 2023-09-03  727  		err = drm_gem_shmem_swapin_locked(shmem);

Or maybe it's because the kbuild bot can't use the cross function db
and shmem->pages is assigned here?

2c607edf57db6a Dmitry Osipenko 2023-09-03  728  		if (err) {
2c607edf57db6a Dmitry Osipenko 2023-09-03  729  			ret = VM_FAULT_OOM;
2c607edf57db6a Dmitry Osipenko 2023-09-03  730  			goto unlock;
2c607edf57db6a Dmitry Osipenko 2023-09-03  731  		}
2c607edf57db6a Dmitry Osipenko 2023-09-03  732  
11d5a4745e00e7 Neil Roberts    2021-02-23 @733  		page = shmem->pages[page_offset];
                                                                       ^^^^^^^^^^^^
Unchecked dereference

2194a63a818db7 Noralf Trønnes  2019-03-12  734  
8b93d1d7dbd578 Daniel Vetter   2021-08-12  735  		ret = vmf_insert_pfn(vma, vmf->address, page_to_pfn(page));
d611b4a0907cec Neil Roberts    2021-02-23  736  	}
d611b4a0907cec Neil Roberts    2021-02-23  737  
2c607edf57db6a Dmitry Osipenko 2023-09-03  738  unlock:
21aa27ddc58269 Dmitry Osipenko 2023-05-30  739  	dma_resv_unlock(shmem->base.resv);
d611b4a0907cec Neil Roberts    2021-02-23  740  
d611b4a0907cec Neil Roberts    2021-02-23  741  	return ret;
2194a63a818db7 Noralf Trønnes  2019-03-12  742  }

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