ghsa-526j-rpwr-89fg
Vulnerability from github
In the Linux kernel, the following vulnerability has been resolved:
x86/mm/pat: Fix VM_PAT handling when fork() fails in copy_page_range()
If track_pfn_copy() fails, we already added the dst VMA to the maple tree. As fork() fails, we'll cleanup the maple tree, and stumble over the dst VMA for which we neither performed any reservation nor copied any page tables.
Consequently untrack_pfn() will see VM_PAT and try obtaining the PAT information from the page table -- which fails because the page table was not copied.
The easiest fix would be to simply clear the VM_PAT flag of the dst VMA if track_pfn_copy() fails. However, the whole thing is about "simply" clearing the VM_PAT flag is shaky as well: if we passed track_pfn_copy() and performed a reservation, but copying the page tables fails, we'll simply clear the VM_PAT flag, not properly undoing the reservation ... which is also wrong.
So let's fix it properly: set the VM_PAT flag only if the reservation succeeded (leaving it clear initially), and undo the reservation if anything goes wrong while copying the page tables: clearing the VM_PAT flag after undoing the reservation.
Note that any copied page table entries will get zapped when the VMA will get removed later, after copy_page_range() succeeded; as VM_PAT is not set then, we won't try cleaning VM_PAT up once more and untrack_pfn() will be happy. Note that leaving these page tables in place without a reservation is not a problem, as we are aborting fork(); this process will never run.
A reproducer can trigger this usually at the first try:
https://gitlab.com/davidhildenbrand/scratchspace/-/raw/main/reproducers/pat_fork.c
WARNING: CPU: 26 PID: 11650 at arch/x86/mm/pat/memtype.c:983 get_pat_info+0xf6/0x110 Modules linked in: ... CPU: 26 UID: 0 PID: 11650 Comm: repro3 Not tainted 6.12.0-rc5+ #92 Hardware name: QEMU Standard PC (Q35 + ICH9, 2009), BIOS 1.16.3-2.fc40 04/01/2014 RIP: 0010:get_pat_info+0xf6/0x110 ... Call Trace: ... untrack_pfn+0x52/0x110 unmap_single_vma+0xa6/0xe0 unmap_vmas+0x105/0x1f0 exit_mmap+0xf6/0x460 __mmput+0x4b/0x120 copy_process+0x1bf6/0x2aa0 kernel_clone+0xab/0x440 __do_sys_clone+0x66/0x90 do_syscall_64+0x95/0x180
Likely this case was missed in:
d155df53f310 ("x86/mm/pat: clear VM_PAT if copy_p4d_range failed")
... and instead of undoing the reservation we simply cleared the VM_PAT flag.
Keep the documentation of these functions in include/linux/pgtable.h, one place is more than sufficient -- we should clean that up for the other functions like track_pfn_remap/untrack_pfn separately.
{
"affected": [],
"aliases": [
"CVE-2025-22090"
],
"database_specific": {
"cwe_ids": [],
"github_reviewed": false,
"github_reviewed_at": null,
"nvd_published_at": "2025-04-16T15:16:03Z",
"severity": null
},
"details": "In the Linux kernel, the following vulnerability has been resolved:\n\nx86/mm/pat: Fix VM_PAT handling when fork() fails in copy_page_range()\n\nIf track_pfn_copy() fails, we already added the dst VMA to the maple\ntree. As fork() fails, we\u0027ll cleanup the maple tree, and stumble over\nthe dst VMA for which we neither performed any reservation nor copied\nany page tables.\n\nConsequently untrack_pfn() will see VM_PAT and try obtaining the\nPAT information from the page table -- which fails because the page\ntable was not copied.\n\nThe easiest fix would be to simply clear the VM_PAT flag of the dst VMA\nif track_pfn_copy() fails. However, the whole thing is about \"simply\"\nclearing the VM_PAT flag is shaky as well: if we passed track_pfn_copy()\nand performed a reservation, but copying the page tables fails, we\u0027ll\nsimply clear the VM_PAT flag, not properly undoing the reservation ...\nwhich is also wrong.\n\nSo let\u0027s fix it properly: set the VM_PAT flag only if the reservation\nsucceeded (leaving it clear initially), and undo the reservation if\nanything goes wrong while copying the page tables: clearing the VM_PAT\nflag after undoing the reservation.\n\nNote that any copied page table entries will get zapped when the VMA will\nget removed later, after copy_page_range() succeeded; as VM_PAT is not set\nthen, we won\u0027t try cleaning VM_PAT up once more and untrack_pfn() will be\nhappy. Note that leaving these page tables in place without a reservation\nis not a problem, as we are aborting fork(); this process will never run.\n\nA reproducer can trigger this usually at the first try:\n\n https://gitlab.com/davidhildenbrand/scratchspace/-/raw/main/reproducers/pat_fork.c\n\n WARNING: CPU: 26 PID: 11650 at arch/x86/mm/pat/memtype.c:983 get_pat_info+0xf6/0x110\n Modules linked in: ...\n CPU: 26 UID: 0 PID: 11650 Comm: repro3 Not tainted 6.12.0-rc5+ #92\n Hardware name: QEMU Standard PC (Q35 + ICH9, 2009), BIOS 1.16.3-2.fc40 04/01/2014\n RIP: 0010:get_pat_info+0xf6/0x110\n ...\n Call Trace:\n \u003cTASK\u003e\n ...\n untrack_pfn+0x52/0x110\n unmap_single_vma+0xa6/0xe0\n unmap_vmas+0x105/0x1f0\n exit_mmap+0xf6/0x460\n __mmput+0x4b/0x120\n copy_process+0x1bf6/0x2aa0\n kernel_clone+0xab/0x440\n __do_sys_clone+0x66/0x90\n do_syscall_64+0x95/0x180\n\nLikely this case was missed in:\n\n d155df53f310 (\"x86/mm/pat: clear VM_PAT if copy_p4d_range failed\")\n\n... and instead of undoing the reservation we simply cleared the VM_PAT flag.\n\nKeep the documentation of these functions in include/linux/pgtable.h,\none place is more than sufficient -- we should clean that up for the other\nfunctions like track_pfn_remap/untrack_pfn separately.",
"id": "GHSA-526j-rpwr-89fg",
"modified": "2025-04-16T15:34:44Z",
"published": "2025-04-16T15:34:44Z",
"references": [
{
"type": "ADVISORY",
"url": "https://nvd.nist.gov/vuln/detail/CVE-2025-22090"
},
{
"type": "WEB",
"url": "https://git.kernel.org/stable/c/8d6373f83f367dbed316ddeb178130a3a64b5b67"
},
{
"type": "WEB",
"url": "https://git.kernel.org/stable/c/b07398e8a5da517083f5c3f2daa8f6681b48ab28"
},
{
"type": "WEB",
"url": "https://git.kernel.org/stable/c/da381c33f3aa6406406c9fdf07b8b0b63e0ce722"
},
{
"type": "WEB",
"url": "https://git.kernel.org/stable/c/dc84bc2aba85a1508f04a936f9f9a15f64ebfb31"
},
{
"type": "WEB",
"url": "https://git.kernel.org/stable/c/de6185b8892d88142ef69768fe4077cbf40109c0"
}
],
"schema_version": "1.4.0",
"severity": []
}
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