From 029ae067431ab9d0fca479bdabe780fa436706ea Mon Sep 17 00:00:00 2001 From: Janusz Krzysztofik Date: Tue, 24 Feb 2026 10:49:06 +0100 Subject: drm/i915: Fix potential overflow of shmem scatterlist length When a scatterlists table of a GEM shmem object of size 4 GB or more is populated with pages allocated from a folio, unsigned int .length attribute of a scatterlist may get overflowed if total byte length of pages allocated to that single scatterlist happens to reach or cross the 4GB limit. As a consequence, users of the object may suffer from hitting unexpected, premature end of the object's backing pages. [278.780187] ------------[ cut here ]------------ [278.780377] WARNING: CPU: 1 PID: 2326 at drivers/gpu/drm/i915/i915_mm.c:55 remap_sg+0x199/0x1d0 [i915] ... [278.780654] CPU: 1 UID: 0 PID: 2326 Comm: gem_mmap_offset Tainted: G S U 6.17.0-rc1-CI_DRM_16981-ged823aaa0607+ #1 PREEMPT(voluntary) [278.780656] Tainted: [S]=CPU_OUT_OF_SPEC, [U]=USER [278.780658] Hardware name: Intel Corporation Meteor Lake Client Platform/MTL-P LP5x T3 RVP, BIOS MTLPFWI1.R00.3471.D91.2401310918 01/31/2024 [278.780659] RIP: 0010:remap_sg+0x199/0x1d0 [i915] ... [278.780786] Call Trace: [278.780787] [278.780788] ? __apply_to_page_range+0x3e6/0x910 [278.780795] ? __pfx_remap_sg+0x10/0x10 [i915] [278.780906] apply_to_page_range+0x14/0x30 [278.780908] remap_io_sg+0x14d/0x260 [i915] [278.781013] vm_fault_cpu+0xd2/0x330 [i915] [278.781137] __do_fault+0x3a/0x1b0 [278.781140] do_fault+0x322/0x640 [278.781143] __handle_mm_fault+0x938/0xfd0 [278.781150] handle_mm_fault+0x12c/0x300 [278.781152] ? lock_mm_and_find_vma+0x4b/0x760 [278.781155] do_user_addr_fault+0x2d6/0x8e0 [278.781160] exc_page_fault+0x96/0x2c0 [278.781165] asm_exc_page_fault+0x27/0x30 ... That issue was apprehended by the author of a change that introduced it, and potential risk even annotated with a comment, but then never addressed. When adding folio pages to a scatterlist table, take care of byte length of any single scatterlist not exceeding max_segment. Fixes: 0b62af28f249b ("i915: convert shmem_sg_free_table() to use a folio_batch") Closes: https://gitlab.freedesktop.org/drm/i915/kernel/-/issues/14809 Cc: Matthew Wilcox (Oracle) Cc: Andrew Morton Cc: stable@vger.kernel.org # v6.5+ Signed-off-by: Janusz Krzysztofik Reviewed-by: Andi Shyti Signed-off-by: Andi Shyti Link: https://lore.kernel.org/r/20260224094944.2447913-2-janusz.krzysztofik@linux.intel.com (cherry picked from commit 06249b4e691a75694c014a61708c007fb5755f60) Signed-off-by: Tvrtko Ursulin --- drivers/gpu/drm/i915/gem/i915_gem_shmem.c | 12 +++++++++--- 1 file changed, 9 insertions(+), 3 deletions(-) diff --git a/drivers/gpu/drm/i915/gem/i915_gem_shmem.c b/drivers/gpu/drm/i915/gem/i915_gem_shmem.c index c6c64ba29bc4..720a9ad39aa2 100644 --- a/drivers/gpu/drm/i915/gem/i915_gem_shmem.c +++ b/drivers/gpu/drm/i915/gem/i915_gem_shmem.c @@ -153,8 +153,12 @@ int shmem_sg_alloc_table(struct drm_i915_private *i915, struct sg_table *st, } } while (1); - nr_pages = min_t(unsigned long, - folio_nr_pages(folio), page_count - i); + nr_pages = min_array(((unsigned long[]) { + folio_nr_pages(folio), + page_count - i, + max_segment / PAGE_SIZE, + }), 3); + if (!i || sg->length >= max_segment || folio_pfn(folio) != next_pfn) { @@ -164,7 +168,9 @@ int shmem_sg_alloc_table(struct drm_i915_private *i915, struct sg_table *st, st->nents++; sg_set_folio(sg, folio, nr_pages * PAGE_SIZE, 0); } else { - /* XXX: could overflow? */ + nr_pages = min_t(unsigned long, nr_pages, + (max_segment - sg->length) / PAGE_SIZE); + sg->length += nr_pages * PAGE_SIZE; } next_pfn = folio_pfn(folio) + nr_pages; -- cgit v1.2.3