DEBIAN-CVE-2021-47531

In the Linux kernel, the following vulnerability has been resolved: drm/msm: Fix mmap to include VMIO and VMDONTDUMP 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 drmgemmmapobj() case where obj->funcs->mmap() was NULL. That meant that we ran: vma->vmflags |= VMIO | VMPFNMAP | VMDONTEXPAND | VMDONTDUMP; vma->vmpageprot = pgprotwritecombine(vmgetpageprot(vma->vmflags)); vma->vmpageprot = pgprotdecrypted(vma->vmpageprot); ...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 vmflags got VMIO / VMDONTDUMP 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, pmd=0000000000000000 Internal error: Oops: 96000006 [#1] PREEMPT SMP [...] CPU: 7 PID: 15734 Comm: crashdump64 Tainted: G W 5.10.67 #1 [...] Hardware name: Qualcomm Technologies, Inc. sc7280 IDP SKU2 platform (DT) pstate: 80400009 (Nzcv daif +PAN -UAO -TCO BTYPE=--) pc : _archcopytouser+0xc0/0x30c lr : copyout+0xac/0x14c [...] Call trace: _archcopytouser+0xc0/0x30c copypagetoiter+0x1a0/0x294 processvmrwcore+0x240/0x408 processvmrw+0x110/0x16c _arm64sysprocessvmreadv+0x30/0x3c el0svccommon+0xf8/0x250 doel0svc+0x30/0x80 el0svc+0x10/0x1c el0synchandler+0x78/0x108 el0sync+0x184/0x1c0 Code: f8408423 f80008c3 910020c6 36100082 (b8404423) Let's add the two flags back in. While we're at it, the fact that we aren't running the default means that we _don't need to clear out VMPFNMAP, so remove that and save an instruction. NOTE: it was confirmed that VMIO was the important flag to fix the problem I was seeing, but adding back VM_DONTDUMP seems like a sane thing to do so I'm doing that too.