CVE-2025-68231

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

mm/mempool: fix poisoning order>0 pages with HIGHMEM

The kernel test has reported:

BUG: unable to handle page fault for address: fffba000 #PF: supervisor write access in kernel mode #PF: errorcode(0x0002) - not-present page *pde = 03171067 *pte = 00000000 Oops: Oops: 0002 [#1] CPU: 0 UID: 0 PID: 1 Comm: swapper/0 Tainted: G T 6.18.0-rc2-00031-gec7f31b2a2d3 #1 NONE a1d066dfe789f54bc7645c7989957d2bdee593ca Tainted: [T]=RANDSTRUCT Hardware name: QEMU Standard PC (i440FX + PIIX, 1996), BIOS 1.16.3-debian-1.16.3-2 04/01/2014 EIP: memset (arch/x86/include/asm/string32.h:168 arch/x86/lib/memcpy32.c:17) Code: a5 8b 4d f4 83 e1 03 74 02 f3 a4 83 c4 04 5e 5f 5d 2e e9 73 41 01 00 90 90 90 3e 8d 74 26 00 55 89 e5 57 56 89 c6 89 d0 89 f7 <f3> aa 89 f0 5e 5f 5d 2e e9 53 41 01 00 cc cc cc 55 89 e5 53 57 56 EAX: 0000006b EBX: 00000015 ECX: 001fefff EDX: 0000006b ESI: fffb9000 EDI: fffba000 EBP: c611fbf0 ESP: c611fbe8 DS: 007b ES: 007b FS: 0000 GS: 0000 SS: 0068 EFLAGS: 00010287 CR0: 80050033 CR2: fffba000 CR3: 0316e000 CR4: 00040690 Call Trace: poisonelement (mm/mempool.c:83 mm/mempool.c:102) mempoolinitnode (mm/mempool.c:142 mm/mempool.c:226) mempoolinitnoprof (mm/mempool.c:250 (discriminator 1)) ? mempoolallocpages (mm/mempool.c:640) biointegrityinitfn (block/bio-integrity.c:483 (discriminator 8)) ? mempoolallocpages (mm/mempool.c:640) dooneinitcall (init/main.c:1283)

Christoph found out this is due to the poisoning code not dealing properly with CONFIG_HIGHMEM because only the first page is mapped but then the whole potentially high-order page is accessed.

We could give up on HIGHMEM here, but it's straightforward to fix this with a loop that's mapping, poisoning or checking and unmapping individual pages.