| From bippy-5f407fcff5a0 Mon Sep 17 00:00:00 2001 |
| From: Greg Kroah-Hartman <gregkh@linuxfoundation.org> |
| To: <linux-cve-announce@vger.kernel.org> |
| Reply-to: <cve@kernel.org>, <linux-kernel@vger.kernel.org> |
| Subject: CVE-2021-47531: drm/msm: Fix mmap to include VM_IO and VM_DONTDUMP |
| |
| Description |
| =========== |
| |
| 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, pmd=0000000000000000 |
| Internal error: Oops: 96000006 [#1] PREEMPT SMP |
| [...] |
| CPU: 7 PID: 15734 Comm: crash_dump64 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 : __arch_copy_to_user+0xc0/0x30c |
| lr : copyout+0xac/0x14c |
| [...] |
| Call trace: |
| __arch_copy_to_user+0xc0/0x30c |
| copy_page_to_iter+0x1a0/0x294 |
| process_vm_rw_core+0x240/0x408 |
| process_vm_rw+0x110/0x16c |
| __arm64_sys_process_vm_readv+0x30/0x3c |
| el0_svc_common+0xf8/0x250 |
| do_el0_svc+0x30/0x80 |
| el0_svc+0x10/0x1c |
| el0_sync_handler+0x78/0x108 |
| el0_sync+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 VM_PFNMAP, so remove that and save |
| an instruction. |
| |
| NOTE: it was confirmed that VM_IO 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. |
| |
| The Linux kernel CVE team has assigned CVE-2021-47531 to this issue. |
| |
| |
| Affected and fixed versions |
| =========================== |
| |
| Issue introduced in 5.15 with commit 510410bfc034c57cc3caf1572aa47c1017bab2f9 and fixed in 5.15.7 with commit 8e2b7fe5e8a4be5e571561d9afcfbd92097288ba |
| Issue introduced in 5.15 with commit 510410bfc034c57cc3caf1572aa47c1017bab2f9 and fixed in 5.16 with commit 3466d9e217b337bf473ee629c608e53f9f3ab786 |
| |
| Please see https://www.kernel.org for a full list of currently supported |
| kernel versions by the kernel community. |
| |
| Unaffected versions might change over time as fixes are backported to |
| older supported kernel versions. The official CVE entry at |
| https://cve.org/CVERecord/?id=CVE-2021-47531 |
| will be updated if fixes are backported, please check that for the most |
| up to date information about this issue. |
| |
| |
| Affected files |
| ============== |
| |
| The file(s) affected by this issue are: |
| drivers/gpu/drm/msm/msm_gem.c |
| |
| |
| Mitigation |
| ========== |
| |
| The Linux kernel CVE team recommends that you update to the latest |
| stable kernel version for this, and many other bugfixes. Individual |
| changes are never tested alone, but rather are part of a larger kernel |
| release. Cherry-picking individual commits is not recommended or |
| supported by the Linux kernel community at all. If however, updating to |
| the latest release is impossible, the individual changes to resolve this |
| issue can be found at these commits: |
| https://git.kernel.org/stable/c/8e2b7fe5e8a4be5e571561d9afcfbd92097288ba |
| https://git.kernel.org/stable/c/3466d9e217b337bf473ee629c608e53f9f3ab786 |
