CVE-2025-39776

In the Linux kernel, the following vulnerability has been resolved:<br /> <br /> mm/debug_vm_pgtable: clear page table entries at destroy_args()<br /> <br /> The mm/debug_vm_pagetable test allocates manually page table entries for<br /> the tests it runs, using also its manually allocated mm_struct. That in<br /> itself is ok, but when it exits, at destroy_args() it fails to clear those<br /> entries with the *_clear functions.<br /> <br /> The problem is that leaves stale entries. If another process allocates an<br /> mm_struct with a pgd at the same address, it may end up running into the<br /> stale entry. This is happening in practice on a debug kernel with<br /> CONFIG_DEBUG_VM_PGTABLE=y, for example this is the output with some extra<br /> debugging I added (it prints a warning trace if pgtables_bytes goes<br /> negative, in addition to the warning at check_mm() function):<br /> <br /> [ 2.539353] debug_vm_pgtable: [get_random_vaddr ]: random_vaddr is 0x7ea247140000<br /> [ 2.539366] kmem_cache info<br /> [ 2.539374] kmem_cachep 0x000000002ce82385 - freelist 0x0000000000000000 - offset 0x508<br /> [ 2.539447] debug_vm_pgtable: [init_args ]: args-&gt;mm is 0x000000002267cc9e<br /> (...)<br /> [ 2.552800] WARNING: CPU: 5 PID: 116 at include/linux/mm.h:2841 free_pud_range+0x8bc/0x8d0<br /> [ 2.552816] Modules linked in:<br /> [ 2.552843] CPU: 5 UID: 0 PID: 116 Comm: modprobe Not tainted 6.12.0-105.debug_vm2.el10.ppc64le+debug #1 VOLUNTARY<br /> [ 2.552859] Hardware name: IBM,9009-41A POWER9 (architected) 0x4e0202 0xf000005 of:IBM,FW910.00 (VL910_062) hv:phyp pSeries<br /> [ 2.552872] NIP: c0000000007eef3c LR: c0000000007eef30 CTR: c0000000003d8c90<br /> [ 2.552885] REGS: c0000000622e73b0 TRAP: 0700 Not tainted (6.12.0-105.debug_vm2.el10.ppc64le+debug)<br /> [ 2.552899] MSR: 800000000282b033 CR: 24002822 XER: 0000000a<br /> [ 2.552954] CFAR: c0000000008f03f0 IRQMASK: 0<br /> [ 2.552954] GPR00: c0000000007eef30 c0000000622e7650 c000000002b1ac00 0000000000000001<br /> [ 2.552954] GPR04: 0000000000000008 0000000000000000 c0000000007eef30 ffffffffffffffff<br /> [ 2.552954] GPR08: 00000000ffff00f5 0000000000000001 0000000000000048 0000000000004000<br /> [ 2.552954] GPR12: 00000003fa440000 c000000017ffa300 c0000000051d9f80 ffffffffffffffdb<br /> [ 2.552954] GPR16: 0000000000000000 0000000000000008 000000000000000a 60000000000000e0<br /> [ 2.552954] GPR20: 4080000000000000 c0000000113af038 00007fffcf130000 0000700000000000<br /> [ 2.552954] GPR24: c000000062a6a000 0000000000000001 8000000062a68000 0000000000000001<br /> [ 2.552954] GPR28: 000000000000000a c000000062ebc600 0000000000002000 c000000062ebc760<br /> [ 2.553170] NIP [c0000000007eef3c] free_pud_range+0x8bc/0x8d0<br /> [ 2.553185] LR [c0000000007eef30] free_pud_range+0x8b0/0x8d0<br /> [ 2.553199] Call Trace:<br /> [ 2.553207] [c0000000622e7650] [c0000000007eef30] free_pud_range+0x8b0/0x8d0 (unreliable)<br /> [ 2.553229] [c0000000622e7750] [c0000000007f40b4] free_pgd_range+0x284/0x3b0<br /> [ 2.553248] [c0000000622e7800] [c0000000007f4630] free_pgtables+0x450/0x570<br /> [ 2.553274] [c0000000622e78e0] [c0000000008161c0] exit_mmap+0x250/0x650<br /> [ 2.553292] [c0000000622e7a30] [c0000000001b95b8] __mmput+0x98/0x290<br /> [ 2.558344] [c0000000622e7a80] [c0000000001d1018] exit_mm+0x118/0x1b0<br /> [ 2.558361] [c0000000622e7ac0] [c0000000001d141c] do_exit+0x2ec/0x870<br /> [ 2.558376] [c0000000622e7b60] [c0000000001d1ca8] do_group_exit+0x88/0x150<br /> [ 2.558391] [c0000000622e7bb0] [c0000000001d1db8] sys_exit_group+0x48/0x50<br /> [ 2.558407] [c0000000622e7be0] [c00000000003d810] system_call_exception+0x1e0/0x4c0<br /> [ 2.558423] [c0000000622e7e50] [c00000000000d05c] system_call_vectored_common+0x15c/0x2ec<br /> (...)<br /> [ 2.558892] ---[ end trace 0000000000000000 ]---<br /> [ 2.559022] BUG: Bad rss-counter state mm:000000002267cc9e type:MM_ANONPAGES val:1<br /> [ 2.559037] BUG: non-zero pgtables_bytes on freeing mm: -6144<br /> <br /> Here the modprobe process ended up with an allocated mm_struct from the<br /> mm_struct slab that was used before by the debug_vm_pgtable test. That is<br /> not a problem, since the mm_stru<br /> ---truncated---