Description
In the Linux kernel, the following vulnerability has been resolved:
mm/damon/ops-common: use a page-aligned address in damon_ptep_mkold()
__damon_va_prepare_access_check() picks a random byte address within the
region and stores it in r->sampling_addr. damon_va_mkold() passes it into
a page table walk, which hands it to damon_ptep_mkold() as the address of
the page to sample:
damon_va_mkold(mm, r->sampling_addr)
damon_va_walk_page_range(mm, addr, addr + 1)
damon_mkold_pmd_entry()
damon_ptep_mkold(pte, vma, addr)
ptep_test_and_clear_young(vma, addr, pte)
mmu_notifier_clear_young(mm, addr, addr + PAGE_SIZE)
For arm64, before commit 6f0e1142173a ("arm64: mm: support batch clearing
of the young flag for large folios"), the contpte helper walked exactly
CONT_PTES entries from the aligned-down page table pointer and used @addr
only to pass down to each entry, so an unaligned value was harmless:
ptep = contpte_align_down(ptep);
addr = ALIGN_DOWN(addr, CONT_PTE_SIZE);
for (i = 0; i < CONT_PTES; i++, ptep++, addr += PAGE_SIZE)
Now the range to walk is derived from @addr instead: end = addr + nr *
PAGE_SIZE, rounded up to CONT_PTE_SIZE. For a sample in the last page of
a contpte block, the sub-page offset puts end just past the block
boundary, so the round-up lands a whole block further and the walk clears
PTE_AF in CONT_PTES entries beyond the sampled block. For the last block
in a page table page, those entries are past the end of that page, so the
walk writes into the page that follows.
Triggered by the full 7.1/7.2 kernel selftest suite on arm64 (EC2
c/m6g.4xlarge). The kernel sometimes crashes at or shortly after the
DAMON test.
What the overrun does depends on the page that happens to follow the page
table, so there is no single signature. If that page is read-only, the
write faults in the sampling path itself:
Unable to handle kernel write to read-only memory at virtual address ffff0003c5d2d000
FSC = 0x0f: level 3 permission fault
CM = 0, WnR = 1, TnD = 0, TagAccess = 0
CPU: 10 UID: 0 PID: 3487 Comm: kdamond.2
pc : contpte_test_and_clear_young_ptes+0x70/0xc0
lr : damon_ptep_mkold+0x1e8/0x1f8
Call trace:
contpte_test_and_clear_young_ptes+0x70/0xc0 (P)
damon_mkold_pmd_entry+0x150/0x170
walk_pmd_range+0x110/0x2b0
walk_pud_range+0x10c/0x208
walk_pgd_range+0x134/0x258
__walk_page_range+0x98/0x1b0
walk_page_range_vma_unsafe+0x90/0x148
walk_page_range_vma+0x28/0x40
damon_va_walk_page_range+0x114/0x2b8
damon_va_prepare_access_checks+0xec/0x1a8
kdamond_fn+0x534/0x770
kthread+0x128/0x138
ret_from_fork+0x10/0x20
Otherwise the page is writable, the PTE_AF clearing succeeds silently and
the damage only surfaces later, in whatever happened to own the page, so
the backtrace is unrelated to DAMON and differs between runs.
Pass a page-aligned address to the ptep_test_and_clear_young() call in
damon_ptep_mkold(), which is the only place DAMON can reach
contpte_test_and_clear_young_ptes() from. Nothing else sees the aligned
address, and r->sampling_addr itself is left as is, so the sampling and
region bookkeeping semantics are unchanged.
mm/damon/ops-common: use a page-aligned address in damon_ptep_mkold()
__damon_va_prepare_access_check() picks a random byte address within the
region and stores it in r->sampling_addr. damon_va_mkold() passes it into
a page table walk, which hands it to damon_ptep_mkold() as the address of
the page to sample:
damon_va_mkold(mm, r->sampling_addr)
damon_va_walk_page_range(mm, addr, addr + 1)
damon_mkold_pmd_entry()
damon_ptep_mkold(pte, vma, addr)
ptep_test_and_clear_young(vma, addr, pte)
mmu_notifier_clear_young(mm, addr, addr + PAGE_SIZE)
For arm64, before commit 6f0e1142173a ("arm64: mm: support batch clearing
of the young flag for large folios"), the contpte helper walked exactly
CONT_PTES entries from the aligned-down page table pointer and used @addr
only to pass down to each entry, so an unaligned value was harmless:
ptep = contpte_align_down(ptep);
addr = ALIGN_DOWN(addr, CONT_PTE_SIZE);
for (i = 0; i < CONT_PTES; i++, ptep++, addr += PAGE_SIZE)
Now the range to walk is derived from @addr instead: end = addr + nr *
PAGE_SIZE, rounded up to CONT_PTE_SIZE. For a sample in the last page of
a contpte block, the sub-page offset puts end just past the block
boundary, so the round-up lands a whole block further and the walk clears
PTE_AF in CONT_PTES entries beyond the sampled block. For the last block
in a page table page, those entries are past the end of that page, so the
walk writes into the page that follows.
Triggered by the full 7.1/7.2 kernel selftest suite on arm64 (EC2
c/m6g.4xlarge). The kernel sometimes crashes at or shortly after the
DAMON test.
What the overrun does depends on the page that happens to follow the page
table, so there is no single signature. If that page is read-only, the
write faults in the sampling path itself:
Unable to handle kernel write to read-only memory at virtual address ffff0003c5d2d000
FSC = 0x0f: level 3 permission fault
CM = 0, WnR = 1, TnD = 0, TagAccess = 0
CPU: 10 UID: 0 PID: 3487 Comm: kdamond.2
pc : contpte_test_and_clear_young_ptes+0x70/0xc0
lr : damon_ptep_mkold+0x1e8/0x1f8
Call trace:
contpte_test_and_clear_young_ptes+0x70/0xc0 (P)
damon_mkold_pmd_entry+0x150/0x170
walk_pmd_range+0x110/0x2b0
walk_pud_range+0x10c/0x208
walk_pgd_range+0x134/0x258
__walk_page_range+0x98/0x1b0
walk_page_range_vma_unsafe+0x90/0x148
walk_page_range_vma+0x28/0x40
damon_va_walk_page_range+0x114/0x2b8
damon_va_prepare_access_checks+0xec/0x1a8
kdamond_fn+0x534/0x770
kthread+0x128/0x138
ret_from_fork+0x10/0x20
Otherwise the page is writable, the PTE_AF clearing succeeds silently and
the damage only surfaces later, in whatever happened to own the page, so
the backtrace is unrelated to DAMON and differs between runs.
Pass a page-aligned address to the ptep_test_and_clear_young() call in
damon_ptep_mkold(), which is the only place DAMON can reach
contpte_test_and_clear_young_ptes() from. Nothing else sees the aligned
address, and r->sampling_addr itself is left as is, so the sampling and
region bookkeeping semantics are unchanged.
Published:
2026-10-23
Score:
n/a
EPSS:
n/a
KEV:
No
Impact:
n/a
Action:
n/a
Analysis
No analysis available yet.
Default status is the baseline for the product, each version can override it (e.g. patched versions marked unaffected).
| Vendor | Product | Default status | Versions | |||||||||||||||
|---|---|---|---|---|---|---|---|---|---|---|---|---|---|---|---|---|---|---|
| Linux | Linux | unaffected |
|
|||||||||||||||
| Linux | Linux | affected |
|
No data.
No data.
No data available yet.
Remediation
No remediation available yet.
Tracking
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Advisories
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References
History
Fri, 23 Oct 2026 12:30:00 +0000
| Type | Values Removed | Values Added |
|---|---|---|
| Description | In the Linux kernel, the following vulnerability has been resolved: mm/damon/ops-common: use a page-aligned address in damon_ptep_mkold() __damon_va_prepare_access_check() picks a random byte address within the region and stores it in r->sampling_addr. damon_va_mkold() passes it into a page table walk, which hands it to damon_ptep_mkold() as the address of the page to sample: damon_va_mkold(mm, r->sampling_addr) damon_va_walk_page_range(mm, addr, addr + 1) damon_mkold_pmd_entry() damon_ptep_mkold(pte, vma, addr) ptep_test_and_clear_young(vma, addr, pte) mmu_notifier_clear_young(mm, addr, addr + PAGE_SIZE) For arm64, before commit 6f0e1142173a ("arm64: mm: support batch clearing of the young flag for large folios"), the contpte helper walked exactly CONT_PTES entries from the aligned-down page table pointer and used @addr only to pass down to each entry, so an unaligned value was harmless: ptep = contpte_align_down(ptep); addr = ALIGN_DOWN(addr, CONT_PTE_SIZE); for (i = 0; i < CONT_PTES; i++, ptep++, addr += PAGE_SIZE) Now the range to walk is derived from @addr instead: end = addr + nr * PAGE_SIZE, rounded up to CONT_PTE_SIZE. For a sample in the last page of a contpte block, the sub-page offset puts end just past the block boundary, so the round-up lands a whole block further and the walk clears PTE_AF in CONT_PTES entries beyond the sampled block. For the last block in a page table page, those entries are past the end of that page, so the walk writes into the page that follows. Triggered by the full 7.1/7.2 kernel selftest suite on arm64 (EC2 c/m6g.4xlarge). The kernel sometimes crashes at or shortly after the DAMON test. What the overrun does depends on the page that happens to follow the page table, so there is no single signature. If that page is read-only, the write faults in the sampling path itself: Unable to handle kernel write to read-only memory at virtual address ffff0003c5d2d000 FSC = 0x0f: level 3 permission fault CM = 0, WnR = 1, TnD = 0, TagAccess = 0 CPU: 10 UID: 0 PID: 3487 Comm: kdamond.2 pc : contpte_test_and_clear_young_ptes+0x70/0xc0 lr : damon_ptep_mkold+0x1e8/0x1f8 Call trace: contpte_test_and_clear_young_ptes+0x70/0xc0 (P) damon_mkold_pmd_entry+0x150/0x170 walk_pmd_range+0x110/0x2b0 walk_pud_range+0x10c/0x208 walk_pgd_range+0x134/0x258 __walk_page_range+0x98/0x1b0 walk_page_range_vma_unsafe+0x90/0x148 walk_page_range_vma+0x28/0x40 damon_va_walk_page_range+0x114/0x2b8 damon_va_prepare_access_checks+0xec/0x1a8 kdamond_fn+0x534/0x770 kthread+0x128/0x138 ret_from_fork+0x10/0x20 Otherwise the page is writable, the PTE_AF clearing succeeds silently and the damage only surfaces later, in whatever happened to own the page, so the backtrace is unrelated to DAMON and differs between runs. Pass a page-aligned address to the ptep_test_and_clear_young() call in damon_ptep_mkold(), which is the only place DAMON can reach contpte_test_and_clear_young_ptes() from. Nothing else sees the aligned address, and r->sampling_addr itself is left as is, so the sampling and region bookkeeping semantics are unchanged. | |
| Title | mm/damon/ops-common: use a page-aligned address in damon_ptep_mkold() | |
| First Time appeared |
Linux
Linux linux Kernel |
|
| CPEs | cpe:2.3:o:linux:linux_kernel:*:*:*:*:*:*:*:* | |
| Vendors & Products |
Linux
Linux linux Kernel |
|
| References |
|
MITRE
Status: PUBLISHED
Assigner: Linux
Published:
Updated: 2026-10-23T12:05:05.149Z
Reserved: 2026-09-25T10:25:14.380Z
Link: CVE-2026-98918
Vulnrichment
No data.
NVD
Status : Received
Published: 2026-10-23T13:17:12.360
Modified: 2026-10-23T13:17:12.360
Link: CVE-2026-98918
Redhat
No data.
OpenCVE Enrichment
No data.
Weaknesses
No weakness.