Affected: Linux

In the Linux kernel, the following vulnerability has been resolved:

drm/msm: Fix mmap to include VM_IO and VM_DONTDUMP

In commit 510410bfc034 ("drm/msm: Implement mmap as GEM object function") we switched to a new/cleaner method of doing things. That's good, but we missed a little bit.

Before that commit, we used to _first_ run through the drm_gem_mmap_obj() case where `obj->funcs->mmap()` was NULL. That meant that we ran:

vma->vm_flags |= VM_IO | VM_PFNMAP | VM_DONTEXPAND | VM_DONTDUMP; vma->vm_page_prot = pgprot_writecombine(vm_get_page_prot(vma->vm_flags)); vma->vm_page_prot = pgprot_decrypted(vma->vm_page_prot);

...and _then_ we modified those mappings with our own. Now that `obj->funcs->mmap()` is no longer NULL we don't run the default code. It looks like the fact that the vm_flags got VM_IO / VM_DONTDUMP was important because we're now getting crashes on Chromebooks that use ARC++ while logging out. Specifically a crash that looks like this (this is on a 5.10 kernel w/ relevant backports but also seen on a 5.15 kernel):

Unable to handle kernel paging request at virtual address ffffffc008000000 Mem abort info: ESR = 0x96000006 EC = 0x25: DABT (current EL), IL = 32 bits SET = 0, FnV = 0 EA = 0, S1PTW = 0 Data abort info: ISV = 0, ISS = 0x00000006 CM = 0, WnR = 0 swapper pgtable: 4k pages, 39-bit VAs, pgdp=000000008293d000 [ffffffc008000000] pgd=00000001002b3003, p4d=00000001002b3003, pud=00000001002b3003…