| 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-2021-47632: powerpc/set_memory: Avoid spinlock recursion in change_page_attr() |
| |
| Description |
| =========== |
| |
| In the Linux kernel, the following vulnerability has been resolved: |
| |
| powerpc/set_memory: Avoid spinlock recursion in change_page_attr() |
| |
| Commit 1f9ad21c3b38 ("powerpc/mm: Implement set_memory() routines") |
| included a spin_lock() to change_page_attr() in order to |
| safely perform the three step operations. But then |
| commit 9f7853d7609d ("powerpc/mm: Fix set_memory_*() against |
| concurrent accesses") modify it to use pte_update() and do |
| the operation safely against concurrent access. |
| |
| In the meantime, Maxime reported some spinlock recursion. |
| |
| [ 15.351649] BUG: spinlock recursion on CPU#0, kworker/0:2/217 |
| [ 15.357540] lock: init_mm+0x3c/0x420, .magic: dead4ead, .owner: kworker/0:2/217, .owner_cpu: 0 |
| [ 15.366563] CPU: 0 PID: 217 Comm: kworker/0:2 Not tainted 5.15.0+ #523 |
| [ 15.373350] Workqueue: events do_free_init |
| [ 15.377615] Call Trace: |
| [ 15.380232] [e4105ac0] [800946a4] do_raw_spin_lock+0xf8/0x120 (unreliable) |
| [ 15.387340] [e4105ae0] [8001f4ec] change_page_attr+0x40/0x1d4 |
| [ 15.393413] [e4105b10] [801424e0] __apply_to_page_range+0x164/0x310 |
| [ 15.400009] [e4105b60] [80169620] free_pcp_prepare+0x1e4/0x4a0 |
| [ 15.406045] [e4105ba0] [8016c5a0] free_unref_page+0x40/0x2b8 |
| [ 15.411979] [e4105be0] [8018724c] kasan_depopulate_vmalloc_pte+0x6c/0x94 |
| [ 15.418989] [e4105c00] [801424e0] __apply_to_page_range+0x164/0x310 |
| [ 15.425451] [e4105c50] [80187834] kasan_release_vmalloc+0xbc/0x134 |
| [ 15.431898] [e4105c70] [8015f7a8] __purge_vmap_area_lazy+0x4e4/0xdd8 |
| [ 15.438560] [e4105d30] [80160d10] _vm_unmap_aliases.part.0+0x17c/0x24c |
| [ 15.445283] [e4105d60] [801642d0] __vunmap+0x2f0/0x5c8 |
| [ 15.450684] [e4105db0] [800e32d0] do_free_init+0x68/0x94 |
| [ 15.456181] [e4105dd0] [8005d094] process_one_work+0x4bc/0x7b8 |
| [ 15.462283] [e4105e90] [8005d614] worker_thread+0x284/0x6e8 |
| [ 15.468227] [e4105f00] [8006aaec] kthread+0x1f0/0x210 |
| [ 15.473489] [e4105f40] [80017148] ret_from_kernel_thread+0x14/0x1c |
| |
| Remove the read / modify / write sequence to make the operation atomic |
| and remove the spin_lock() in change_page_attr(). |
| |
| To do the operation atomically, we can't use pte modification helpers |
| anymore. Because all platforms have different combination of bits, it |
| is not easy to use those bits directly. But all have the |
| _PAGE_KERNEL_{RO/ROX/RW/RWX} set of flags. All we need it to compare |
| two sets to know which bits are set or cleared. |
| |
| For instance, by comparing _PAGE_KERNEL_ROX and _PAGE_KERNEL_RO you |
| know which bit gets cleared and which bit get set when changing exec |
| permission. |
| |
| The Linux kernel CVE team has assigned CVE-2021-47632 to this issue. |
| |
| |
| Affected and fixed versions |
| =========================== |
| |
| Fixed in 5.15.34 with commit 6def4eaf0391f24be541633a954c0e4876858b1e |
| Fixed in 5.16.20 with commit 96917107e67846f1d959ed03be281048efad14c5 |
| Fixed in 5.17.3 with commit 6ebe5ca2cbe438a688f2ae238ef5a0b0b5f3468a |
| Fixed in 5.18 with commit a4c182ecf33584b9b2d1aa9dad073014a504c01f |
| |
| 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-2021-47632 |
| 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: |
| arch/powerpc/mm/pageattr.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/6def4eaf0391f24be541633a954c0e4876858b1e |
| https://git.kernel.org/stable/c/96917107e67846f1d959ed03be281048efad14c5 |
| https://git.kernel.org/stable/c/6ebe5ca2cbe438a688f2ae238ef5a0b0b5f3468a |
| https://git.kernel.org/stable/c/a4c182ecf33584b9b2d1aa9dad073014a504c01f |
