Thank you for your contribution! Sashiko AI review found 3 potential issue(s) to consider:
Pre-existing issues: - [Critical] Missing VMA boundary check in panthor PMD mapping insertion causes kernel panic or memory overlap. - [High] Incorrect GEM object page offset calculation causes mapping corruption on VMA split or partial unmap. - [High] Normal refcounted shmem folios are mapped using raw PFN helpers, improperly marking them as special. -- commit 07cb1bde7a0031ea636a380e71bef2ca1d93de8c Author: Christian A. Ehrhardt <[email protected]> drm/shmem_helper: Check VMA boundaries for PMD mappings This commit adds a boundary check in the try_insert_pfn() function to ensure that a PMD huge page mapping is not installed if it exceeds the boundaries of the VMA. > In the ->huge_fault handler do not install a PMD huge page > mapping if the huge page exceeds the boundaries of the VMA. > > All other ->huge_fault handlers have similar checks and the > resulting mapping will trigger a VM_BUG_ON_VMA() if it ever > reaches copy_pmd_range(). [Severity: Critical] This is a pre-existing issue, but does panthor_gem.c also need this fix? Looking at insert_page() in drivers/gpu/drm/panthor/panthor_gem.c at line 802, it inserts a PMD mapping if the address is aligned, but it lacks the vma->vm_start <= start && end <= vma->vm_end bounds check: } else if (order == PMD_ORDER) { unsigned long pfn = page_to_pfn(page); unsigned long paddr = pfn << PAGE_SHIFT; bool aligned = (vmf->address & ~PMD_MASK) == (paddr & ~PMD_MASK); if (aligned && folio_test_pmd_mappable(page_folio(page))) { pfn &= PMD_MASK >> PAGE_SHIFT; return vmf_insert_pfn_pmd(vmf, pfn, vmf->flags & FAULT_FLAG_WRITE); } If userspace mmaps the panthor GEM object, shrinks the VMA to a non-PMD-aligned size using munmap(), and triggers a page fault at a PMD-aligned address near the end before calling fork(), couldn't this cause a VM_BUG_ON_VMA() in copy_pmd_range() or allow memory overlap? > diff --git a/drivers/gpu/drm/drm_gem_shmem_helper.c > b/drivers/gpu/drm/drm_gem_shmem_helper.c > index c989459eb2159..00807039f8d7d 100644 > --- a/drivers/gpu/drm/drm_gem_shmem_helper.c > +++ b/drivers/gpu/drm/drm_gem_shmem_helper.c > @@ -597,9 +597,13 @@ static vm_fault_t try_insert_pfn(struct vm_fault *vmf, > unsigned int order, > #ifdef CONFIG_ARCH_SUPPORTS_PMD_PFNMAP > } else if (order == PMD_ORDER) { > unsigned long paddr = pfn << PAGE_SHIFT; > + struct vm_area_struct *vma = vmf->vma; > + unsigned long start = ALIGN_DOWN(vmf->address, PMD_SIZE); > + unsigned long end = start + PMD_SIZE; > + bool in_range = vma->vm_start <= start && end <= vma->vm_end; > bool aligned = (vmf->address & ~PMD_MASK) == (paddr & > ~PMD_MASK); > > - if (aligned && > + if (aligned && in_range && > folio_test_pmd_mappable(page_folio(pfn_to_page(pfn)))) { > vm_fault_t ret; > > @@ -608,8 +612,10 @@ static vm_fault_t try_insert_pfn(struct vm_fault *vmf, > unsigned int order, > * .huge_fault(). Make sure we pass the "write" info > * along in that case. > * This also means we have to record the write fault > * here, instead of in .pfn_mkwrite(). > */ [Severity: High] This isn't a bug introduced by this patch, but are we improperly marking normal refcounted shmem folios as special? The try_insert_pfn() function uses raw PFN insertion helpers like vmf_insert_pfn_pmd() and vmf_insert_pfn() to map these folios. According to MM guidelines, this marks the folios with VM_PFNMAP and pte_special(), which hides them from vm_normal_page() and breaks GUP (get_user_pages) and refcount tracking. Should this code use vmf_insert_folio() or vmf_insert_page() instead? > - ret = vmf_insert_pfn_pmd(vmf, pfn, > - vmf->flags & FAULT_FLAG_WRITE); > + ret = vmf_insert_pfn_pmd(vmf, pfn, > + vmf->flags & FAULT_FLAG_WRITE); > + if (ret == VM_FAULT_NOPAGE && (vmf->flags & > FAULT_FLAG_WRITE)) > + drm_gem_shmem_record_mkwrite(vmf); [Severity: High] This is a pre-existing issue, but does drm_gem_shmem_record_mkwrite() calculate the page offset incorrectly when a VMA is split? In drm_gem_shmem_record_mkwrite() at line 576 (and also in drm_gem_shmem_any_fault() at line 640), the page offset is calculated relative to the current VMA rather than the GEM object: pgoff_t page_offset = vmf->pgoff - vma->vm_pgoff; ... folio_mark_dirty(page_folio(shmem->pages[page_offset])); If userspace partially unmaps the beginning of the VMA via munmap(vma->vm_start, PAGE_SIZE), the VMA split increments vma->vm_pgoff. Because vmf->pgoff - vma->vm_pgoff evaluates exactly to (vmf->address - vma->vm_start) >> PAGE_SHIFT, this completely ignores the split offset and accesses pages[0] for the new VMA instead of the correct shifted page. Could this cause mapping corruption by marking the wrong page dirty or exposing the wrong memory pages? > > return ret; > } -- Sashiko AI review ยท https://sashiko.dev/#/patchset/[email protected]?part=1
